The kingdom PROTISTA and its 45 phyla

BioSystems, 17 (1984) 87--126 87 Elsevier Scientific Publishers Ireland Ltd.

THE KINGDOM PROTISTA AND ITS 45 PHYLA*,**

JOHN O. CORLISS

Department of Zoology, University of Maryland, College Park, MD 20742, U.S.A.

(Received March 23rd, 1984) (Revised version received July 24th, 1984)

Because most recent treatments of the protists ( ' lower ' eukaryotes comprising the kingdom PROTISTA Haeckei, 1866) have been preoccupied with either a 'phylogenetic-tree ' approach or a discussion of the impact of possible endosymbiotic origins of major intracellular organelles, the overall systematics of the group, from taxonomic and nomenelatural points of view, has been almost total ly neglected. As a result, confusion over contained phyla, their places in a classification scheme, and even their names (and authorships) is growing; the situation could become chaotic. The principal objective of the present paper is to recognize the taxonomic inter- relationships among all protist groups; and it includes the specific proposal that some 45 phyla, defined and characterized, be assigned to 18 supraphyletic assemblages within the kingdom PROTISTA (itself redefined and contrasted with the other eukaryotic kingdoms recognized here: ANIMALIA, PLANTAE and FUNGI). Vernacu- lar terms are employed for identification of the 18 assemblages, but defensible formal names are proposed at the level of phylum. None is presented as new: authorship-and-date credits are given to preceding workers on the taxonomy of the many groups involved. By presenting taxonomic characterizations as well as relevant nomenclatural data for each taxon described, a comprehensive scheme of overall higher-level classification within the kingdom emerges that may be considered to serve as a solid base or ' taking-off point ' for future discussions.

The 18 supraphyletie groups and their phyla (in parentheses and including authorships and dates of their formal names) are as follows: I. The rhizopods (phyla Karyoblastea Margulis, 1974; Amoebozoa Liihe, 1913; Acrasia Van Tieghem, 1880; Eumycetozoa Zopf, 1885; Plasmodiophorea Zopf, 1885; Granuloreticulosa De Saedeleer, 1934; incertae sedis Xenophyophora Schulze, 1904). II. The mastigomyeetes (Hypochytr id iomycota Sparrow, 1959; Oomycota Winter, 1897; incert, sed. Chytr id iomycota Sparrow, 1959). III. The chlorobionts (Chlorophyta Pascher, 1914; Prasinophyta Christensen, 1962; Conjugatophyta Engler, 1892; Charophyta Rabenhorst , 1863; incert, sed. Glaucophyta Bohlin, 1901). IV. The euglenozoa (Euglenophyta Pascher, 1931; Kinetoplastidea Honigberg, 1963; incert, sed. Pseudociliata Corliss & Lipscomb, 1982). V. The rhodophytes (Rhodophyta Rabenhorst, 1863). VI. The cryptomonads (Cryptophyta Pascher, 1914). VII. The choanoflagel- lares (Choanoflagellata Kent, 1880). VIII. The chromobionts (Chtysophyta Pascher, 1914; Haptophyta Christensen, 1962 ; Bacillariophyta Engler & Gild, 1924 ; Xanthophyta Allorge in Fritsch, 1935; Eust igmatophyta Hibberd & Leedale, 1970; Phaeophyta Kjellman, 1891; incert, seal. Proteromonadea Grass~ in GrassY, 1952). IX. The labyrinthomorphs (Labyrinthulea Cienkowski, 1867; Thraustochytriacea Sparrow, 1943 [possibly infraphyletic rank?]). X The polymastigotes (Metamonadea Gras~ in GrassY, 1952; Parabasalia Honigberg, 1973). XI. The paraflagellates (Opalinata Wenyon, 1926). XII. The actinopods (Heliozoa Haeckel, 1866; Taxopoda Fol, 1883; Acantharia Haeckel, 1879; POlycystina Ehrenberg, 1839; Phaeodaria Haeckel, 1879). XIII. The dinoflagellates (Peridinea Ehrenberg, 1830; Syndinea Chatton, 1920). XIV. The eiliates (Ciliophora Doflein, 1901). XV. The sporozoa (Sporozoa Leuckart, 1879). XVI. The microsporidia (Microsporidia Balbiani, 1882). XVII. The haplosporidia (Haplosporidia Caullery & Mesnil, 1899). XVIII. The myxosporidia (Myxosporidia Biitschli, 1881; incert, sed. Actinomyxidea ~tolc, 1899 [perhaps not separate phylum? ] ).

Key words: Protists; Algae; Protozoa; 'Lower ' fungi; Kingdoms; Phyla; Systematics; Nomenclature

*This paper is based in part on an invited presentation made at the Fifth Meeting of the International Society for Evolutionary Protistology, which was convened in Banyuls-sur-Mer, France, 6--9 June 1983. **Support of National Science Foundat ion grants DEB 79-23440 and BSR 83-07113 is gratefully acknowledged.

0303-2647/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

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'There's more to [eukaryotic] life than [just] animals and plants.' (Corliss, 1983a) 'A taxonomic system is a road to further progress, not a monument to our little gains.' (F.C. Page, unpublished) 'We need many more data before planting more trees!' {E.G. Merinfeld, unpublished}.

1. Introduction and Objectives

In these times of such renewed interest on the part of many biologists in eukaryogenesis, on the one hand, and the evolutionary origin of the more complex multicellular eukaryotes from the 'lower' eukaryotes, on the other, it is natural for attention to be focussed on the pivotal group, the protists. A rash of stimulating books and papers has appeared within the past half-dozen years attesting to the growing popularity of topics ranging from the biochemistry and fine structure of protist subcellular components to the possible phylogenetic and evolutionary relationships among whole groups of the better known algae and protozoa and other often neglected taxa of such non-tissue- forming organisms. The celebrated Serial Endosymbiosis Theory has enjoyed a remark- able renaissance. And even certain systematic and taxonomic reshufflings, based mainly on ultrastructural and molecular data formerly not available, have occasionally been given consideration.

Some six dozen selected recent references, often .very rich in bibliographic citations of their own, may be mentioned here as explicit evidence of the literature explosion following the heuristic earlier works by modern<lay pioneers like Copeland (1956), Margulis (1970} and Whittaker (1969): Amos and Duckett {1982), Bardele (1983), Barnes (1984}, Barr {1981), Cachon and Cachon (1974), Cavalier-Smith (1978,1981a,b, 1982a,b, 1983), Corliss (1981, 1983b), Cox (1980), Demoulin (1979), Dillon (1981), Dayhoff and Schwartz {1981}, Dodge (1973, 1979), Edwards (1976}, Frederick (1981}, Fuller (1976), Goode (1981}, Gray and Doolittle

(1982), Hanson (1977), Heath (1980, 1981), Hibberd (1976a,b, 1979, 1981, 1984}, Jeffrey (1982}, Jeon (1983), Joysey and Friday (1982), Krylov (1981), Lazarus {1984), Leedale (1974), Lynn (1981}, Mahler and Raft (1975}, Margulis (1974a,b 1981a), Margulis and Schwartz (1982}, Margulis et al. (1984}, Matsuno et al. (1984), Melkonian (1982a,b), Moestrup (1982), MShn (1984}, Olive (1975}, Parker (1982), Pickett-Heaps (1975}, Ragan and Chapman (1978}, Raikov {1982}, Round (1980}, Schenk and Schwem- ruler (1983), Schwemmler and Schenk (1980), Sleigh (1979), Stewart and Mattox (1975}, Tappan {1980), Taylor {1974, 1976a,b, 1978, 1979, 1980a,b), Whatley et al. {1979), Whatley and Whatley (1981}, Whittaker (1977), and Whittaker and Margulis (1978}. Many more individual papers could be listed.

In view of the foregoing statements and citations -- not to mention the quotations at the head of this paper -- why still yet another discussion of protists at this particular time? The principal reason is that one of the missing topics in the literature to date has been an overall comprehensive taxonomic approach, quite apart from preoccupation with phylogenetic trees and/or the endosymbiotic origin of cytoplasmic organelles. Such an approach should embrace in its treatment the many and diverse taxa of all the many and diverse organisms considered to be deserving of the title 'protist'.

The most important objective of the present paper is to tackle seriously the major high-level taxonomic and nomenclatural problems presented in recognition of a kingdom Protista and to provide a rationale in defense of the splitting of the rather few protist taxa generally recognized at the phyletic level into a multiplicity of groups at that rank. Along with this goal, I feel that I must first (re)- define, albeit briefly, the kingdoms that contain these and the other phyla of known organisms. Quite often, even the most ardent proponents of a separate kingdom of protists have characterized it in a negative fashion. For example, Margulis and Schwartz {1982}

state, 'Kingdom Protoctista is defined by exclusion: its members are neither an imals . . . p l a n t s . . , f u n g i . . , nor prokaryotes. ' And the many new protist phyla created in recent years (e.g., see Cavalier-Smith, 1981a; Jeffrey, 1982; Margulis, 1974b; Whittaker and Margulis, 1978) have of ten been named without comment or comparative diagnoses, a situation that could rapidly lead to Chaos.

Some degree of taxonomic and nomenclatural stabilization needs to be brought about. For didactic and pedagogical reasons, if for no others, the tide of proposals involving drastic nomenclatural changes typically left unexplained in the texts o f the papers containing them ought to be stemmed. The number of likely phyla of protists must be high; this is defensible on evolutionary grounds, but, somehow, it must be rendered palatable to researcher, teacher, and student alike. One of the principal suggestions of the present paper is to retain as many established group-names as possible to avoid the confusion otherwise ultimately resulting. This should slow down the present incredible ' taxonomic mobil i ty ' among major high-level protist g r o u p s . .

Based on evolutionary considerations, I am grouping my 45 phyletic taxa into 18 supraphyletic assemblages. But I am employing only vernacular, informal, or familiar (thus non-capitalized) names for those supraphyletic groupings, purposely avoiding the creation of still another formal level (subkingdom, superphylum, or the like) in the hierarchy and the addition of a lot of new formal Latinized names to the already nomenclaturally over- burdened system. The annotated classification scheme appearing as the last section of this paper provides in a single place a sorely needed taxonomic framework for the higher- level systematics of the kingdom overall.

Another goal here -- perhaps really more a plea -- is to urge adoption of the name Protista for the organisms under discussion rather than 'Protoctista. ' Not only are the arguments over priority, over what exactly did Hogg (1860), Haeckel (1866, 1878),

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Copeland (1938, 1956), and others include under or mean by the names they used, etc. disputable but also the insistence by some modern workers that protist obligatorily implies very minute (and only very minute) organisms and is therefore totally unacceptable is a specious argument as well. Consider the metazoa: for every mammal the size of a cow, there are a thousand species of insects requiring a hand lens for identification. For every giant kelp species, cannot it be said that there are a thousand microscopic protists? Size is hardly a valid evolutionary argument for either separating groups or for determin- ing the name of their all-embracing taxon. Protista and protist also have the t remendous value of simplicity and of etymological, not to mention popular, appeal. If one believes at all in the concept of a separate kingdom for the ' lower' eukaryotes, then the name should be as simple a descriptive handle as possible.

Finally, I should also like to take the oppor tuni ty here to correct a rather grave misinterpretation of my preceding 'packaging' paper (Corliss, 1981). The five supraphyletic groupings discussed there represented the actual, conventional situation that of ten still obtains today. That is, consciously or otherwise, most protozoologists, phycologists, and mycologists think of protist species as belonging or assignable to discrete and taxonomically totally separate high-level categories, which I discussed using only vernacular names for them. Protists have been considered to be either members of a distinct protozoan group, or an algal group, or a 'protozoalgal' group (i.e., forms claimed as protozoa by zoologists and simultaneously embraced as algae by botanists), or a lower fungal group, or -- paralleling the situation for some algae and protozoa -- a 'protozofungar group. Some colleagues seemed to believe that I was formally supporting and even erecting as new and as a good idea those five artificial groups in that paper of mine (Corliss, 1981). Quite the contrary! While pointing out their very real existence, I was strongly decrying that fact and urging the reader to ' think protist '

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and drop those ou tmoded categories of 'Protozoa, ' 'Algae,' and 'Lower Fungi' -- to which one should add ' T h a l l o p h y t a ' - or any combination of them !

Controversial though some of the conclusions that I have drawn in the present paper may be, they can serve well as an outline of a skeletal scheme of classification for the Protista useful in future discussion. Prelimi- nary announcements of certain of the matters treated in extenso here have already been published, mostly in the form of brief abstracts related to oral presentations made at professional meetings (e.g., see Corliss, 1982a,b, 1983b,c). I have profited from colleagues' critical comments offered on or following such occasions, as reflected in modifications incorporated at appropriate places below.

2. The Four Eukaryotic Kingdoms Redefined

It is axiomatic in taxonomy that the higher the hierarchical rank the fewer are the diffe- rential characters required. The four kingdoms of the superkingdom Eukaryota possess in common a membrane-bound nucleus containing discrete chromosomes composed of DNA, RNA, and proteins. While others could be listed, this property alone is sufficient to recognize the great irreversible evolutionary separation of eukaryotes from the Prokaryota. That the latter superkingdom is probably itself divisable into several kingdoms (Archae- bacteria, Eubacteria, etc.} is of no concern to us here, although mention should be made that the 'algal' Prochloron and the 'blue- greens' (cyanobacteria), as prokaryotes, are not considered 'algae' at all and are thus not included in the present paper. With respect to total numbers of species, incidentally, the figure typically given for the validly described kinds of bacteria sensu lato today is in the range of only 3-5000: this may be contrasted with numbers given for the eukaryotic groups in Tables 1--4.

The principal criterion that ! apply fpr recognizing four distinct high-level units of

organisms within the Eukaryota is the kind and degree of cellular organization. Combina- tions of other characters may be considered as well (see Tables 1 - - 4 ) - presence or absence of (certain types of) cell walls, e t c . - but the presence of more than a single true, functional tissue is limited to animals and plants (the only groups of vascular organisms), with the former showing a still higher degree of histological complexity, differentiation, and diversity (organs, etc.) than found in the latter. The fungi may manifest quite complex development of their mycelia, but these never function as fundamentally distinctive multiple tissues in the vegetative stage. The true fungi are also unique in their complete absence of flagella or cilia, their possession of chitinous cell walls, and in their having vegetative stages t h a t are haploid and dikaryotic. The protists, while showing multicellularity to varying degrees in certain groups, and occasionally even huge body size, again fail to demonstrate the organization of cells into two or more clearly differentiated functional tissues.

While the majority of the Protista may be thought of as 'prisoners of their unicellu- laxity,' they have actually evolved internal and external complexities -- cytoarchitectures -- far more diverse than can be found among members of the other three eukaryotic kingdoms. At the same time, not unexpectedly, the protists show flexibility or plasticity in modes of nutrition, running the gamut from autot rophy to heterotrophy, in organization of their mitochondrial cristae, in kinds of locomotion, etc. Above the level of this kingdom, the most ancient membership of which may have formed the ancestral breeding ground for the evolutionary origin of those organisms now comprising all three of the other kingdoms, nutritive methods serve as useful distinctive characters: animals are primarily and commonly (although not exclusively) phagotrophic heterotrophs; plants are autotrophs, with rare secondary loss of chloroplasts; and fungi are exclusively osmotrophic heterotrophs. And all three conglome- rates are believed to show basically only

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TABLE 1

Kingdom ANIMALIA Linnaeus, 1753: diagnosis, with principal distinguishing characteristics, and brief general description

Eukaryotic organisms without cell walls, with more than one type or kind of tissue, and exhibiting a heterotrophic (primarily phagotrophic) mode of nutrition unless autotrophically adapted due to presence ~)f phototrophic or chemotrophic endosymbionts or xenosomes. Also, species assignable here are commonly macroscopic in size and always multicellular, demonstrating highly differentiated organization at the tissue and organ level, and almost without exception showing complex embryological development during ontogeny, with inclusion of identifiable blastula and gastrula stages. In animals properly studied to date, gap junctions have been found to be universally present between cells of tissues. Mitochondrial cristae are flattened or plate-like, with the notable exception of cells of the adrenal cortex of vertebrates. The amino-adipic acid (AAA) pathway is used in lysine synthesis. Gametic meiosis is the rule. A great majority of animals are motile. Some 1 500 000 valid species, fossil and contemporary, have been recorded to date, and/but it is claimed that roughly 10 000 new forms are described annually.

flattened or plate-like cristae in their mitochondria (a curious major exception being found in cells o f the adrenal cortex of vertebrates}.

Thus the Protista are neither mini-plants nor mini-animals nor a combinat ion of the two. As stressed in an earlier paper (Corliss, 1981}, its 120 000 species should not, in my opinion, be viewed as merely a transient stage -- or level of o r g a n i z a t i o n - bridging the gap between prokaryotes and higher eukaryotic groups. They have an integrity and taxonomic and phylogenetic cohesiveness of their own. That the chlorobionts (the 'Chloro- phyte Series'}, for example, gave rise to the Plantae is no reason, of itself, to insist that, therefore, such ancestral protists must be included within the latter kingdom. In fact, a common misconception about protist groups is that all of them must have appeared

in to to first (before any species of plants, animals, or fungi) on the face of the earth. Although that vast sub jec t is beyond the scope of the present paper, the general

observat ion ought to be made that very likely many present-day protist assemblages evolved long after the origin of various groups of the other kingdoms. The fossil record, unfortunately, is in general frustratingly unhelpful in such particular considerations.

3. Composition of the Kingdom Protista

Once the diversity of the protists has been appreciated, there comes the necessity -- and didactic desirability -- of recognizing subdivisions within their kingdom: no easy task. Inspection of even the most conservative conventional contemporary classifications of the major algal and protozoan groups reveals that

TABLE 2

Kingdom PLANTAE Linnaeus, 1753: diagnosis, with principal distinguishing characteristics, and brief general description

Eukaryotic organisms with cell walls composed of cellulose, with more than one type or kind of tissue, and exhibiting of autotrophic (phototrophic with chlorophylls a and b) mode of nutri t ion unless, in rare cases, chloroplasts have been secondarily lost. Also, species assignable here are commonly macroscopic in size and are always multicellular and vascular (except bryophytes), demonstrating a high degree of organization at the tissue level (typically: roots, stems, leaves). They have their plastids surrounded by two membranes only. Mitochondrial cristae are flattened or plate-like. The diaminopimelic acid (DAP) pathway is used in lysine synthesis. Gametic meiosis is the rule. The great majority of plants have adapted a sedentary terrestrial life, with vegetative or trophic forms therefore seldom motile. Nearly 500 000 species (minus 'algae' now, of course), fossil and contemporary, have been described.

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TABLE 3

Kingdom FUNGI Linnaeus, 1753: diagnosis, with principal distinguishing characteristics, and brief general description

Eukaryotic organisms with chitinous cell walls, a mycelial organization of vegetative cells fundamentally not representing more than a single kind of tissue, and exhibiting an exclusively osmotrophic type of heterotrophic (i.e., nonphotosynthetic) nutrition. Also, species assignable here are often macroscopic in size and always multicellular (unless secondarily reduced to unicellularity) at some stage in the life cycle. The filamentous or hyphal (coenocytic or septate) organization of fungi can result in production of a quite complex thallus (mycelium), but it never reaches a stage of differentiation recognizable as multiple tissues; and there are no vascular fungi. Mitochondrial cristae are flattened or plate-like, and Golgi cisternae are not stacked. The amino-adipic acid (AAA) pathway is used in lysine synthesis. Zygotic meiosis is the rule. Without pseudopodia, flagella, or cilia (or even centrioles) at any stage of the life cycle, true fungi are only passively motile. Some 100 000 species, fossil (rare) and contemporary, have been described.

multiple phyla (or divisions) are widely agreed as being required by the great evolutionary and taxonomic differences now apparent between and among their contained groups. For the protozoa alone, we have witnessed an increase from one to seven phyla within a 15-year period (see Honigberg et al., 1964, and compare its scheme of classification with that endorsed by Levine et al., 1980). Simi- larly, the phychologists have been actively describing new classes and, often, elevating classes old or new to the rank of division (e.g., notice treatments and literature references in Rosowski and Parker, 1971, 1982), with such expansions commencing in the early 1960's.

Modem knowledge is clearly obliging us to recognize that red algae, dinoflagellates, euglenozoa, brown algae, labyrinthomorphs, sporozoa, and myxosporidia -- to mention only several obvious cases -- can no longer be treated as members of a single phylum nor even be assigned to just a few embracing taxa at that rank. Their unique characteristics demand total separation at the phyletic level.

Workers have not tackled the overall problem from a comprehensive, comparative taxonomic point of view, as mentioned above in the Introduction. For example, in Taylor's {1978) important paper, the concentration was on the possible phylogenetic interrela-

TABLE 4

Kingdom PROTISTA Haeckel, 1866: diagnosis, with principal distinguishing characteristics, and brief general description

Eukaryotic organisms with no more than one tissue at most. In fact, species assignable here are predominantly unicellular in organization and microscopic in size. Also, the relatively few syncytial, coenocytic, coenobial, or multicellular forms (generally in the form of filaments, hyphae, colonies, coenobia, or thalli) are still without organization into multiple tissue types. Macroscopic sizes are reached among species of a few groups, but differentiated tissue stages again are absent; and there are no vascular forms. Motile species (often biflagellated or multiciliated or with pseudopodia at some stage in the life cycle) are considerably more numerous and more widespread throughout the contained taxa than nonmotile species. Protists as a group exhibit all modes of nutrition, with both phototrophic (using various chlorophylls) and heterotrophic (phagotrophic, pinocytotic, osmotrophie) forms common. Mitochondrial cristae are tubular, lamellar (flattened), or discoidal. Either the amino-adipic (AAA) or the diaminopimelic acid (DAP) pathway is used in lysine synthesis. Meiosis may be gametic, zygotic, or sporic. Of a difficult-to-determine total number of species described, extinct and extant, some 120 000 may tentatively be considered valid and acceptable, with another 80 000 (mostly fossil 'forams, ' actinopods, desmids, and especially diatoms) highly questionable; but many tens of thousands of distinct species of all sorts remain to be discovered and/or properly described.

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tionships of groups of 'lower' eukaryotes and not on their precise standings or ranks. Even the papers and books by Margulis and Whittaker (e.g., Margulis, 1970, 1974a,b, 1981a,b; Margulis and Schwartz, 1982; Whittaker, 1969, 1977; Whittaker and Margulis, 1978), which have had such a great impact on the whole field, have, again, been more interested in supposed evolutionary relationships than in classification schemes per se. Names used to designate the groups under discussion have generally been plucked from the modern (but conventional) literature, using endings (suffixes) often unchanged from those favored by other authors. Completely new names may (happen to) be proposed, but when they have been, that fact is seldom indicated. It is important to note that even w h e n ranks are drastically changed no special comment has been made, and the reader is given no information concerning the possible shift in concepts involved, let alone the original authorships or dates of the names or the previous standings of the groups bearing such names in recent taxonomic treatises by specialists. Barnes {1984), Leedale (1974), Sleigh {1979), Stewart and Mattox (1980), and others have also generally used selected formal names already available, but without discussion of the whys or wherefores.

The proposals of workers such as Cavalier- Smith (e.g., 1981b) and Jeffrey (1982) have included a number of entirely newly created groups, with new names. Yet, again, with rare exceptions (e.g., Cavalier-Smith, 1981b, has formally characterized three of his new k ingdoms in Latin -- Chromista, Biliphyta, and Viridiplantae -- at the end of his paper), the groups have not been specifically identified as new nor has there been any discussion of the taxonomic-nomenclatural impact or implications of such significant actions. On the contrary, however, the authors in Levine et al. (1980) have carefully supplied nomenclatural details, authors-and~lates, etc., and have indicated what high-level groups they consider to be new to science (although I am not in agreement with all of their proposals).

While practically all of the works briefly mentioned above have professed the 'arti- ficiality' of separating many algal and protozoan groups from one another, they themselves have been guilty of doing just that ! For example, Cavalier-Smith (1981b) writes of 'botanical' (Chromista, Cryptophyta, Chromo- phyta, Biliphyta, Viridiplantae) kingdoms and 'zoological' (Animalia, Euglenozoa, Protozoa [including Dinozoa]) kingdoms. Jeffrey (1982) deliberately labels his high-level groups as e i ther phyla or divisions, with the comment that doing so will be helpful to the reader as an indication of which Code of Nomenclature should be used for the organisms involved. And Whittaker and Margulis (1978), early champions of the uniqueness of the kingdom Protista, nevertheless divide its phyla into three distinct groups labeled Branch Proto- phyta, Branch Protomycota and Branch Protozoa, an action that, in effect, perpetua- tes the myth of mini-plants, mini-animals, etc.

A number of the evolutionary biologists cited above have conscientiously kept in mind the growing concern that too large a number of separate high-level groupings are being endorsed from the point of view of effective teaching at the college or university, as well as highschool, level. Admittedly, students are not apt to appreciate having to become acquainted with so many different names for organisms that they will have little oppor- tunity to get to know well. Cavalier-Smith (1981b), for example, while espousing nine kingdoms in his text, includes a final table containing a reduced number - - f i v e - - o f amalgamated (eukaryotic) kingdoms for teaching purposes (viz., Fungi, Animalia, Protista, Plantae, Chromista). And Whittaker and Margulis (1978) produce 'a more manage- able number of units for biology teachers and students' by use of nine superphyla or form- superphyla, generally informally proposed and 'frankly polyphyletic': Chromophyta or Chromobionta, Chlorophyta or Chloro- bionta, Rhodophyta, Mastigomycota, Gymno- mycota, Sporozoa, Sarcodina, Zoomastigina, and Ciliophora. Margulis and Schwartz

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(1982), however, state simply, 'We propose 27 protoctist phyla'; and no attempt at higher grouping is made. Barnes (1984: chapter on protists was prepared by Sleigh, Dodge and Patterson) also offers 27 (but not the identical) phyla. In the present paper, I propose 18 supraphyletic assemblages to contain my 45 phyla, thus supplying a smaller number of 'super-groupings' with quite familiar vernacular names (see Table 5 ).

Seldom do any kingdom- and phyla-listing works, such as those mentioned above, provide the s o u r c e of their nomenclature; and rarely do they use names that may have been proposed by each other for the same groupings. In the latter case, it may well have been true that many of the papers were independently in press at just about the same time during those protistologically turbulent years of 1978- -1981 . But this is still another reason

T A B L E 5

S u m m a r y o f the p r o p o s e d t a x o n o m i c a r r a n g e m e n t a n d sugges t ed n o m e n c l a t u r e f o r t he 4 5 p h y l a ass igned to 18 a s s e m b l a g e s o f t he k i n g d o m P R O T I S T A Haecke l , 1 8 6 6

I n c l u d e d in t he t o t a l n u m b e r 4 5 are five a p p e n d e d p h y l a l i s ted he re u n d e r t he d e s i g n a t i o n inccrtae sedis: X e n o p h y o p h o r a , l i t t le- k n o w n g r o u p , poss ib ly c o r r e c t l y a t t a c h a b l e to t he r h i z o p o d a s semblage ; C h y t r i d i o m y c o t a , wel l k n o w n b u t q u e s t i o n a b l y u n d e r t he m a s t i g o m y c e t e s b e c a u s e n o t as close to e i t he r of t he o t h e r t w o p h y l a p l a c e d the re as t h e y are to e a c h o t h e r ; G l a u c o p h y t a , p e r h a p s a p h y l u m of c h l o r o b i o n t s , p e r h a p s t o t a l l y i n d e p e n d e n t , p e r h a p s on ly a p o l y p h y l e t i c c o l l e c t i o n o f gene ra ; P s e u d o c i l i a t a , a u n i q u e l i t t l e - s tud ied g r o u p w i t h s o m e c h a r a c t e r s he ld in c o m m o n w i t h b o t h e u g l e n o p h y t e s a n d k i n e t o p l a s t i d e a n s ; lhtotero- m o n a d e a , a r a t h e r i l l -def inable g r o u p , p e r h a p s e m b r a c e a b l e b y e i t h e r t he c h r o m o b i o n t s o r t he p o l y m a s t i g o t e s . Poss ib ly A c t i n o - m y x i d e a deserves p h y l u m r a n k , u n d e r t h e m y x o s p o r i d i a (see A d d e n d u m t o th i s p a p e r ) ; y e t T h r a u s t o c h ] r t t i a c e a , a l a b y r i n t h o - m o r p h , m a y n e e d to he r e d u c e d in s t a tu s : t h u s the n u m b e r o f p h y l a c o u l d r e m a i n a t 45 .

Rhi zopods K a r y o b l a s t e a Margul is , 1 9 7 4 A m o e b o z o a Li ihe , 1 9 1 3 Acras i a Van T i e g h e m , 1 8 8 0 E u m y c e t o z o a Z o p f , 1 8 8 5 P l a s m o d i o p h o r e a Z o p f , 1 8 8 5 G r a n u l o r e t i c u l o s a De Saede lee r , 1 9 3 4 (Incert. sed.: X e n o p h y o p h o r a Schu lze , 1 9 0 4 )

Mas tigom yce tes H y p h o c h y t r i d i o m y c o t a S p a r r o w , 1 9 5 9 O o m y c o t a Win te r , 1 8 7 9 (Incert. sed.: C h y t r i d i o m y c o t a S p a r r o w , 1 9 5 9 )

Chlorobion ts C h l o r o p h y t a Pasche r , 1 9 1 4 P r a s i n o p h y t a C h r i s t e n s e n , 1 9 6 2 C o n j u g a t o p h y t a Engler , 1 8 9 2 C h a r o p h y t a R a b e n h o r s t , 1 8 6 3 (Incert. se~d.: G l a u c o p h y t a Boh l in , 1 9 0 1 )

Euglenozoa E u g l e n o p b y t a Pascbe r , 1 9 3 1 K i n e t o p l a s t i d e a H o n i g b e r g , 1 9 6 3 (Incert. sed.: Pseudoe i l i a t a Corl iss a n d L i p s c o m b , 1 9 8 2 )

R h o d o p h y t e s R h o d o p h y t a R a b e n h o r s t , 1 8 6 3

Cryptornonads C r y p t o p h y t a P a s c h e r , 1 9 1 4

Choanoflagellates C h o a n o f l a g e l l a t a K e n t , 1 8 8 0

C h r o m o b i o n t s C h r y s o p h y t a Pascher, 1914 Haptophyta Christensen, 1962 Bacillariophyta Engler and Gild, 1924 Xanthophyta Allorge in Fritsch, 1935 Eustigmatophyta Hibberd and Leedale, 1970 Phaeophyta Kjellman, 1891 (Ineert. sed.: Pzoteromonadea Grassd in Grassd, 1952

Bicosoecidea Grass6 and Deflandre in Grassd, 1952

Heterochloridea Pascher, 1912 Raphidophyceae Chadefaud, 1950)

Labyrinthornorphs Labyrinthulea Cienkowski, 1867 Thraustochytziacea Sparrow, 1943

Polyrnastigotes M e t a m o n a d e a Grassd in Grassd, 1 9 5 2 P a r a b a s a l i a H o n l g b e r g , 1 9 7 3

Paraflagellates O p a l i n a t a W e n y o n , 1 9 2 6

A c t i n o p o d s Heliozoa H a e c k e l , 1 8 6 6 Taxopoda Fol, 1 8 8 3 A c a n t h a r l a H a e c k e l , 1 8 7 9 P o l y c y s t i n a E h r e n b e r g , 1 8 3 9 P h a e o d a r i a H a e c k e l , 1 8 7 9

Dinoflagellates Per id inea E h r e n b e r g , 1 8 3 0 S y n d i n e a C h a t t o n , 1 9 2 0 (Incert . sed.: E b r i i d e a D e f l a n d r e in Grassd, 1 9 5 2

E l l o b i o p h y c e a e L o e b l i c h III, 1 9 7 0 A c r i t a r c h a Evi t t , 1 9 6 3 )

Ciliates C i l i o p h o r a Dof le in , 1 9 0 1

SPorozoa S p o r o z o a L e u c k a r t , 1 8 7 9 (lncert . sed.: Pe rk in s ida Levine , 1 9 7 8 )

Microsporidia M i c r o s p o r i d i a Ba lb ian i , 1 8 8 2

Haplosporidia H a p l o s p o r i d i a Cau l le ry a n d Mesnil , 1 8 9 9

M y x osp oridia M y x o s p o r i d i a B~itschli, 1 8 8 1 (Incert. sed.: A c t i n o m y x i d e a ~ to lc , 1 8 9 9

Mar te i l i idea D e s p o r t e s a n d G i n s b u r g e r - Voge l , 1 9 7 7

P a r a m y x i d e a C h a t t o n , 1 9 1 1 )

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why we should now stand back and take a fresh overview of the situation.

4. Rationale for Nomenclatural Practices Adopted

Exactly what names to employ for what groups -- at the higher taxonomic l e v e l s - represents a problem exceedingly more com- plicated than is appreciated by most phycologists, protozoologists, and protistologists. One of the difficulties is related to the several Codes of Nomenclature (see below), which, however, serve so well for maintenance of stability and universality of names of plants and animals at the lower levels in the taxonomic hierarchy, particularly for species and genera (Corliss, 1982c). Above the family level, considerable flexibility has traditionally existed, although the International Code of Botanical Nomenclature (1983} seems to be moving toward more uniformity in t reatment of suprafamilial names with its latest recommendations concerning typification and application of priority to typified names (and see Hibberd, 1981; Silva, 1979, 1980}. Certain zoologists are also proposing some more ex- acting guidelines for suprafamilial nomenclature (e.g., see Brothers, 1983, and references therein), but their new Code (in press) will not reflect this.

Protistologists are faced with at least three dilemmas. Adherence to any newly proposed set of very stringent rules would cause exces- sive name-changing. But failure to have some generally acceptable guidelines will lead to increased chaos, with unchecked promot ion of new names. And wholesale retention of older names, including acknowledgement of the original authors and dates involved, may conflict with proper recognition of changing concepts with respect to limits or boundaries of a given high-level taxonomic group. A fourth problem relates to our need to adjust to the Computer Age: only with a stabilized nomenclatural system can we hope to benefit from literature searches, taxonomic data retrieval, and the like. As Silva {1980) has

stated in a paper rich in important nomenclatural details with respect to algal families and classes, the overriding consideration should be effectiveness of communication.

Using names in a vernacular form allows for greater flexibility, and I am maintaining that modus operandi with respect to the identification of the supraphyletic assemblages en- domed in this paper, Clearly descriptive, widely known, easily recognizable, generally long accepted, these names should offend few and yet can serve a good purpose in conveni- ently circumscribing a collection of protist taxa purposely grouped together on the basis of a high degree of commonal i ty in possession of major characteristics of evolutionary significance.

Difficulties arise in considering the taxa that I am listing formally as the 45 phyla comprising the kingdom Protista. How does one give them names that simultaneously break no rules or recommendations, honor the past yet do not slight new concepts, well represent the groups descriptively, embrace precepts of common-sense and courtesy (Corliss, 1972), provide clarity to all con- cerned, and stand as universally familiar and acceptable labels? From a puristic point of view, those conditions in combination would make the job literally impossible. Some sort of compromising rationale is inevitable. A few background observations must be made first, as briefly as possible:

(i) Many of the groups that I am designat- ing as phyla have long been claimed by botanists as plants and have been given ranks -- and names with appropriate suffixes -- at such high levels as class and division (or phylum, a term persistently -- and com- mendably -- long used by some phycologists, e.g., Round, 1965, 1973). Such groups (i.e., their naming here} generally have not presented great difficulties from conceptual and nomenclatural points of view.

(ii) Many of the phyletic groups that have long rested in the zoological domain, however, have previously been limited to ranks at the ordinal or even familial level. Elevating

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such taxa to phyla raises knot ty problems with respect to authors (and dates) of their names, particularly in view of the expanded conceptual understanding of the group of organisms involved.

(iii) Some names are so common in the literature that their authorship is practically 'auctt . ' (the classical 'of authors ' or 'of the literature'), although I consider this historical solution to be an unsatisfactory one from a formal nomenclature viewpoint.

(iv) Probably w i t h o u t e x c e p t i o n the groups assigned the rank of phylum in this paper have in the past had both their names (especially suffixes) and conceptual characteriza- t ions (including, therefore, what subgroups they comprise or do nottcomprise) emended and amended,dozens if not scores of times since their first recognition as a taxon at any suprageneric level! Other than totally replacing such taxonomic names with completely new ones, with or without legalistic or ethical justification (Corliss, 1972), one must arbitra- rily choose appropriate authorships and dates or end up with the absurdity of a whole string of authors' names interconnected by 'emend' or 'sensu'.

The rationale behind the moderate nomenclatural solutions proposed in the present paper is illustrated in the following decisions:

(1) Most of the former botanical classes that are raised to phylum (equivalent to division} status are treated as follows: the suffix -phyta is added to the (former} base, replacing the typical class ending of -phyceae. But the name and group are n o t claimed as a n o v u m p h y l u m (the authori ty for which would have to be cited as 'Corliss, 1984' in the future). Rather, the authorship and date of authorship used are those generally associable with the first person in years past to competently employ the (base of the) name with respect to essentially the same (or if lower rank, coextensive) taxon, perhaps some- what increased or decreased in contained sub- units though it may be today. If all synony- mies, full or partial, were given, they would

wastefully occupy many lines of print (and would often represent a source of confusion to nonspecialist readers}, so only a few are supplied. And no Latin diagnoses are provided.

(2) In general, I am not endorsing newer names (or newer authors-and-dates) if/when the changes have been minor or proposed as replacements in order to be automatically typified (by being based on the name of a currently contained genus) or to 'improve' the name descriptively. Priority is much more of a guiding principle for me than aesthetics or the precise meaning of the Latinized word. Major conceptual changes in the taxon (beyond merely elevating it to the next higher rank or so), have, however, served as a reason for my favoring use of a newer over an older name, but only in a very few cases. For computer-retrieval needs (and the like) important newer names unaccepted by me are included as (junior} synonyms. Concepts and nomenclatural rules should not be confused: nomenclature rightly serves only as a handmaiden to taxonomy, and thus no use of a particular name should be construed as restricting the freedom of taxonomic thought or action (Corliss, 1982c).

(3) Certain (mostly zoological) names that were created at familial or ordinal levels at a t ime when those were very high ranks and that have continued to represent essentially the same groups or kinds of organisms {i.e., the groups may be considered coextensive, as mentioned under point 1, above) are not changed substantially etymologically nor given more recent dates-and-authorships in my quite uniform elevation of them to the phylum-level. For none of the 45 phyla suggested below am I claiming to be the author of the name listed, although well I might if I were endorsing a rigidly puristic nomenclatural philosophy, such as that held today by a nu.mber of influential botanists and, perhaps to a lesser extent, zoologists.

(4) I am not in favor of forcing absolutely un i form endings {suffixes) on names of the

highest (e.g., phyla) taxa of organisms. By chance, all names at the phyletic level in this paper do end in -a. Also, mostly to retain names reasonably familiar to protistologists of all kinds, I have often used the suffix -phyta, on the one hand, and -zoa (or -ata, -idea, or -idia), on the other hand, although I decry -- and deny -- their apparent 'plant' or 'animal' connotations. In cases of the familiar -mycetes termination of the literature, I have changed it to read -mycota (s ince-mycetes has classically indicated class rather than division or phylum rank), an ending having the same good and bad connotat ions o f - p h y t a and -zoa, viz., reasonable familiarity to the reader but possibly false phylogenetic implications. .

(5) Some very high-ldvel names, time- honored and popular thofigh they may be, have deliberately been dropped as formal taxonomic categories. These include Protozoa, Thallophyta, Algae, Phycomycetes , and Lower Fungi (with capital initial letters), plus Sarcomastigophora, Sarcodina, Radiolaria, Phytomastigophora,* Zoomastigophora, Api- complexa, and Myxozoa (the last two are preserved as junior synonyms). The reasons are several, including the fact that (most of) these are unnecessary, misleading, misinter- pretable, and highly inappropriate in their implications. Some are still convenient to use, on occasion, as vernacular terms, especially 'algae' and 'protozoa ' {with lower case initial letters).

*Even the widely k n o w n vernacular t e rm ' p h y t o - f lagel late ' shou ld be e m p l o y e d wi th cau t ion . A n u m b e r of algal groups conven t iona l l y inc luded unde r t ha t head ing are far f rom being 'plant-like' flagellates, even if t hey have plas t ids of some k ind in the i r cy to- plasm. Inc identa l ly , pe rhaps n o t a bad subs t i t u t e for ' phy to f l age l l a t e s ' - - one at least w i t h o u t phy logene t i c c o n n o t a t i o n s -- wou ld be the t e rm inadve r t en t ly conce ived (i.e., it was or iginal ly a typograph ica l e r ror in the typesc r ip t of the MS!) by the a u t h o r in a paper pub l i shed early last year (Corliss, 1983a) , viz., ' p h o t o - f lagel late . ' The word is app rop r i a t e ly usable in reference to those m a n y mobi l e species of p ro t i s t s possessing the abi l i ty to carry o u t pho tosyn thes i s .

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(6) No generic name is simultaneously used, in the identical form, as the formal name of a suprafamilial taxon (e.g., Plasmo- diophora is a genus within a phylum with the deliberately modified name Plasmodiophorea).

5. Inadequacies of Present Codes of Nomen- clature

As mentioned very briefly above, the Inter- national Code of Botanical Nomenclature (1983) [for the most part] and the Interna- tional Code of Zoological Nomenclature (1964) -- not to mention the codes for bacteria and viruses -- simply do not include treatment of problems of (the names for) higher taxa. Furthermore, strictly speaking, such standard codes could be considered inappropriate or even ineligible as vehicles for application to high-level protist names (Corliss, 1983b} since, for many people, the adjective botanical implies solely ' true' plants and zoological, ' true' animals and the protists are neither mini-plants nor mini-animals (Corliss, 1983a) and now enjoy a totally separate kingdom status.

The inadequacies of the major international Codes, in their current forms, become especially clear, even for the nomenclature at the infrafamilial taxonomic levels, with respect to those protist species that have long been treated as 'protozoalgal ' forms {thus as both 'animals' and 'plants,' simultaneously). Inconsistent t reatment of cases involving dinoflagellates (as one of several outstanding affected groups) represents an example of an intolerable situation.

From a pragmatic point of view, there would appear to be four possible solutions to this major 'Code Problem':

Agreement on a s idle unified code for all eukaryotic (and possibly prokaryotic as well) organisms. This would be the ideal, utopian answer, the ecumenical approach.

Harmonization of existing codes on a case- by-case basis. That is, legislate agreement on sticky or controversial nomenclatural cases, as they are brought up for attention, by modi-

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fication of one code or another. Such emended provisions of a given code would allow certain exceptions to its own basic rules, favoring a solution to the particular protist- related problem involved.

Arbitrary allocation to existing codes of members of given protist phyla. For example, all members of the dinoflagellate and eugleno- zoan assemblages could, by tacit agreement, be assigned to the Zoological Code for any nomenclatural problems; and species of chlorobionts ahd chromobionts could be treated solely by provisions of the Botanical Code.

Finally, new and separate codes could be developed and/or recognized for each and every eukaryotic kingdom accepted by the biological communi ty . The protists and fungi might well be allowed to break away from the two major traditional codes, taking with them, of course, species formerly claimed as ' lower' plants or animals.

Without further discussion here, one can nevertheless easily perceive grave problems in attempting to successfully bring about any of the above solutions, in light of the many controversial issues and cries of distress that would immediately arise among the specialist- taxonomists inevitably involved and affected. Nonetheless, something has to be done (see Corliss, 1983b). (A commit tee has been organized by the International Union of Biological Sciences to tackle the overall problem, and a progress report -- at least -- is expected to be presented at the next meeting of the I.U.B.S. General Assembly scheduled for September 1985 in Budapest, Hungary.)

6. Bases for Separation of High-level Groups

Of the dozens of more or less distinctive characters available for my supraphyletic assemblages of protists, and for the 45 phyla themselves, only the most salient -- a chosen few -- will be used in the classification section of this paper for the obvious reasons of space, clarity, and simplicity. Sources of most data are also not directly

cited in the brief characterizations, for the same reasons. But principal papers on which I have relied heavily are referred to elsewhere, in either preceding or following sections. While following my own Constellation of Characters Hypothesis (Corliss, 1976), many of my conclusions tentatively presented here stem from a synthetic approach that is largely qualitatively subjective and intuitively speculative in nature. I am currently planning a quantitatively extensive cladistic analysis of multiple characters that should result in a more objective t reatment of the major taxonomic units comprising the kingdom. I have no doubt but that some changes and refinements in my present scheme will be indicated at the conclusion of that long-range study.

The principal categories exploited in my (continuing) search for a still larger number of useful and usable taxonomic-phylogenetic characters (including the 'semes' of Hanson, 1977) are, in general terms and with some inevitable overlapping, these:

(1) Flagellar and ciliary characteristics. These are numerous and include ultrastructural features on the outside [such as flagellar hairs {e.g., see Moestrup, 1982) and scales, and even freeze-fracture-seen structures of the ciliary membrane (Bardele, 1983)] as well as on the inside (paraxial rod, transitional helix at level of basal body, etc.). There are also many grosset characters of value; for example, those related to numbers, location, kinds of insertion, distributional patterns on the body , lengths, stage of occurrence in the organism's life history, etc. of the various flagella and cilia, as they occur singly or in groups, present on many species of protists.

(2) Basal bodies, centrioles, and associated cortical or peUicular structures or organelles. Kinds, presence or absence, mode of origin, morphogenesis, etc. of these and more or less related organelles {such as rootlets and extrusomes), all composed generally of either microfibrils or microtubules (or even membranes), provide multiple characteristics useful in comparative studies of many protist

groups. See such relevant works as those by Barr (1981), Brugerolle (1975), Lynn (1981), Melkonian (1980}, Moestrup (1982), and Pitelka (1974), to cite a few.

(3) Pseudopodial features and cytoskeletal structures o f diverse kinds. Important for many groups are the comparative data on kinds, uses, distribution, etc. of such organelles and cytostructures associated with various protist species, especially those belonging to the old 'sarcodinid' and 'actinopod' super- assemblages.

(4) Mitochondria and features o f their structure and function. Particularly useful has been the configuration of the cristae formed by the infolding of the inner mitochondrial membrane: for example, tubular (in cross- section} versus lamellar {flattened) or discoidal forms. Cavalier-Smith (1981b), Seravin (1980), Stewart and Mattox {1980) and Taylor {1978}, for example, have done much to excite phylogenetic interest in such specific ultrastructural features.

(5) Characters o f the plastids sensu lato. This includes ultrastructural features as well as the biochemical and molecular nature of the contained pigments, the number of enclosing membranes, the storage products produced, the associated DNA, etc. Data on eyespots or ocelli and related structures could be included here, too. Many phycologists, particularly, have contributed to our knowledge of such characters: for example, see the numerous chapters in the book edited by Cox (1980).

(6) Characters o f the Golgi apparatus (including its presence or absence). Golgi bodies or dictyosomes have had a long and sometime controversial history of study, but their various features are useful in comparative protistology today.

(7) Nuclear characteristics. Numerous are the structural, functional, and genetic features of protist nuclei. And here also one could consider the types of mitosis and meiosis and the spindle-fiber-centriolar relationships possibly involved (not to mention numbers and kinds of nuclei, numbers of chromosomes,

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etc.~. Raikov's (1982) monograph offers the most recent summary on protozoan nuclei; see also Fuller (1976), Goode (1981), Heath (1980), Kubai (1975), Oakley (1978), and Pickett-Heaps (1974), on the evolution of mitosis.

(8) Broad ecological and behavioral characteristics. A vast number of subcategories exist here, ranging from general adaptive 'life style' features or 'strategies' (including cyst or spore formation, colonial or multicellular forms, presence of tests or loricae, development of organeUes of attachment, and symbiotic relationships when appropriate) to overall life cycles, from modes of nutrition to kinds of locomotion, and from types of morphogenesis (including stomato- genesis, production of 'larval' forms, and polymorphism in general) to exhibition of diverse asexual and sexual patterns of reproduction. Many contributions could be cited as examples, including some mycological and parasitological works often overlooked by evolutionists and phylogeneticists. And Margulis' (1970, 1976, 1981a) tremen- dous books and reviews deserve special mention here.

(9) Finally, specific biochemical and molecular features. Many of these are con- cerned with particular metabolic pathways (early realized by Vogel, 1964) used by the various groups of organisms. Also rRNA homologies (Kumazaki et al., 1983), cytochrome c similarities, cell wall composition, pigments, food storage products, membrane studies, and the roles of cytoplasmic or nuclear xenosomes (Corliss, 1984) can be considered under this broad heading. Ragan and Chap- man's {1978) stimulating book set the stage for many subsequent studies, research often carried out by experimentalists or specialists in molecular biology who might not be protistologists at all, though using protist material.

7. Numbers of Species of Protists

A word is in order about numbers of species comprising each of my 'super' groups

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and of each of the included phyla as well. In attempting to determine the composit ion of the principal protist assemblages with respect to named species, I have had to keep in mind three sorts of plaguing problems that have probably been responsible for the tremen- dous shortage of reliable data on the subject in the literature. First is the matter o f living vs. fossil species (with the subproblem of whether the fossil forms described have been derived from extinct lines or from contemporary species with both living and fossilized specimens); of ten the few counts that have been published on given groups do not indicate whether or not both kinds have been included. Secondly, and even graver, is the matter of described species (a highly objective number, since it refers solely to descriptions of new species that have appeared in published works) vs. valid or correct species (a very subjective number, since the count here is one based on the strict- ness or leniency of acceptance by a subsequent specialist or reviewer of earlier species descriptions). Recall that species and their names can be rejected, in effect, on either taxonomic or nomenclatural grounds. Thirdly, how authoritative are the sources of information utilized to supply allegedly reliable figures to the pursuer of such data, and have any of the better sources been inadvertently overlooked?

The Zoological Record and other such compendia are, by their own admission, incomplete with respect to total world coverage of the literature on protists (and they are not always up to date). Authors of monographs may be highly selective in groups covered or are often known to be either splitters or lumpers in their taxonomic philosophy. How many names have been thrown into synonymy (and, thus, their species 'amalgamated')? On the other hand, how many species have been split taxonomically into two or more separate species? And what about subspecies (nomenclaturally treated as species under the Zoological Code)? What about figures in the literature that have been

attached to a major group that now has itself been either split apart into multiple new high- level taxa or dispersed and embraced, fully or partially, by one (or more) other already existing group(s)?

Notwithstanding these obstacles to accu- rate species-counting, I believe that I was reasonably successful in gathering sufficient data to publish quite reliable numbers in my tabular abstract of two or three years ago (Corliss, 1982b). There is little need basically to alter many of them, according to further investigations by myself and helpful comments received from numerous colleagues, although I have tried in the present paper to make clearer whether my figures refer to the category of described or valid (acceptable) species. My estimates generally refer to the second category, unless otherwise indicated. Some changes have resulted from fresh concepts of the boundaries of a given group, and others from the receipt of new estimates provided to me by specialists whose opinions I respect.

While conservative protozoologists and phycologists may consider my numbers (totalling 120 000 for the whole kingdom) to be on the high side, I believe that any fault in that direction is balanced by the combination of missed descriptions and of species more or less obviously in need of splitting. And left to one side are the whole matters of the likelihood of many 'known' but offi- cially still unidentified species and of the incredibly enormous additional numbers that may long await discovery and description simply because of a distinct shortage in availability of taxonomically trained protistologists.

8. Some Protist Terminology

A very brief remark or two needs to be made concerning the terminology endorsed in the present paper. In general, the reader is referred to the very recent glossary of some 800 terms compiled by Corliss and Lom (1984). While those definitions are labeled 'protozoological, ' an effort was made to

include some conventional phycological and mycological terminology there as well, since no comprehensive protistological glossary has yet been published.

When formal scientific names ending in -zoa are expressed in the vernacular plural form, the two words are identical {i.e., have the same spelling) except that the familiar term commences with a lower-case letter (e.g., the phylum Sporozoa contains sporozoan species known as sporozoa, not 'sporozoans'). By the same token, the Microsporidia are comprised of microsporidia, not 'microspori- dians.' And species of coccidia are to be found in the class or subclass Coccidia. On the other hand, among the ciliates the subclass Suctoria contains suctorians, not 'suctoria': there can exist a single sporozoon or microsporidium or coccidium, but there is no 'suctorium' in our scientific vocabulary.

The term 'undulipodia, ' used by some (e.g., Margulis and Schwartz, 1982) as a single com- bining word for both the flagella of eukaryotic flagellates and the cilia of ciliates, is not accepted here (for brief discussion, see Corliss, 1980b). Incidentally, Cavalier-Smith (1981b) prefers the single term 'cilia' for both organelles, while various other workers in the past have favored 'flagella' as the all-embracing descriptive word. But I see no reason for any radical defection from conventional usage. For me, Paramecium is ciliated, being covered with cilia, and Euglena is biflagellate, bearing two flagella; opalinids and some hypermastigotes bear many flagella, while some ciliates possess few cilia (indeed, suctorians have none in their trophic stage}. Pro- karyotes simply have bacterial or prokaryotic flagella: there is no need at all for these non- homologous ultrastructurally different and less complex organelles to be confused with the well known '9 + 2' structured eukaryotic flagella and cilia.

Finally, as mentioned very briefly in a preceding section, the '-phyta, ' ' -mycota ' and '-zoa' suffixes appearing in connection with some of the phyletic names endorsed in the present paper are not to be considered as

I01

implying very close plant or fungal or animal affinities, although that was their former (and, indeed, still is their literal) meaning. Such names have been retained for reasons of recognizability and historical continuity. If they must be taken as informational it, nature (and reflecting something of phylogenetic significance), let their former meanings be expanded a bit to have a generalized nutri- tional implication. Then '-phyta' may be considered plant-like in indicating an autotrophic mode of nutrition; ' -mycota, ' a fungal-like mode, that is, heterotrophic of the subcategory osmotrophic (saprophytic, saprozoic); and '-zoa,' animal-like, heterotrophic but typically of the subcategory phagotrophic.

O. Sources of Literature for Present Overview

Highly helpful to me, directly and indirectly, has been a group of recent 'edited' books, mult iauthored reviews, and special monographs. I have not always cited the individual authors of the included separate sections of the books, but they are invariably authorities and expert specialists in their own area or on their own taxonomic groups of protists. Parker {1982) should be singled out as the most comprehensive and the most in- clusive of 30 or so works listed below. It is also one of the most recent and it covers practically all of the groups, although they are of ten differently named and much more con- servatively arranged taxonomically than they are in the present paper.

The edited and multi-authored works referred to above include Amos and Ducket t (1982), Barnes {1984), Buczacki {1983), Buetow {1982), Cox (1980) [like Parker, 1982, a collection {though smaller) of contributions deserving special mention] , Frederick (1981), Hutner and Bleyman (1979), Jeon {1983), Krylov {1981), Krylov and Starobogatov (1980), Lee et al. (1984), Levandowsky and Hutner (1979--81), Margulis et al. (1984), Morris (1981), Parker {1982), Schenk and Schwemmler (1983) and

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Schwemmler and Schenk (1980). Of slightly older vintage, but also still most useful sources of usable information, are Ainsworth et al. (1973}, Bulla and Cheng (1976, 1977), Hedley and Adams {1974 --78), Jeon (1973}, Kreier (1977--78), Lumsden and Evans {1976, 1979}, de Puytorac and Grain (1974), Sleigh {1974) and Stewart (1974).

Although I have examined many more textbooks than are reasonable to cite here, several deserve specific mention: for example, Alexopoulos and Mims (1979}, Bold et al. (1980), Bold and Wynne (1978), Brock (1979), Chapman and Chapman (1973), GreU (1973), Jahn et al. (1979), Kudo (1966}, Lee {1980}, Poindexter (1971), Pritchard and Bradt (1984), Round (1973), Scagel et al. (1982), Sleigh (1973}, Stainer et al. (1976) and van den Hock {1978). The following specialized monographs, generally published during the past 8--10 years, have also been most helpful: Anderson (1983), Brugerolle (1977), Cachon and Cachon (1974), Casper {1974), Christensen (1980), Corliss (1979a), Dillon (1981), Dodge {1973), Grain (1969), Grass~ and Layette {1978}, H~inel (1979), Haq and Boersma {1978}, Hollande and Carruette-Valentin (1971), Joyon and Mignot (1969), Karling (1968), Lloyd (1974), Margulis and Schwartz {1982), Murray (1973), Nanney (1980), Ogden and Hedley (1980), Olive (1975), Page (1976a,b, 1983), Parke and Dixon (1976), Pickett-Heaps (1975), Ragan and Chapman (1978)~ Sarjeant (1974}, Schiff (1982), Scholtyseck (1979}, Sieburth (1979), Sprague (1977), Tappan (1980), Tendal (1972), van Wagtendonk {1974) and Warner {1977).

In addition, hundreds of scattered papers have been consulted during preparation of the present paper. Generally beyond ones referred to directly on preceding pages (or indirectly via the multi-authored books cited above under only their editors' names), some others, often recent and of a review nature, should be listed briefly here (their diverse subject matters are usually very clear from their

titles): Aufderheide et al. (1980), Bamforth (1981), Bardele (1972, 1975, 1977), Barr (1980), BrugeroUe and Joyon {1976), Brugerolle and Mignot (1979), Brugerolle and Taylor (1979), Buck {1981), Cachon and Balamuth (1979), Cachon and Cachon (1978), Chadefaud (1976), Cole (1979), Corliss (1979b, 1980a), Curds {1982}, Curds et al. (1983), Davidson (1982), Demoulin (1974), Desportes and Lom (1981), Dodson {1971, 1979), Duckett and Peel {1978), Ehret {1960), Fenchel (1969, 1982), Fot t (1974}, Frankel (1983), Fuller (1976), Gibbs {1981), Giddings et al. (1983}, Goll and Merinfeld (1979): Gray and Doolittle {1982), Hanson (1976), Hausmann (1978), Heath (1976), Hibberd (1975, 1979, 1981, 1984), Hibberd and Leedale {1972), Hollande et al. (1969, 1971), Honigberg (1983), Honigberg et al. (1981L Jahn et al. (1974), Jeffrey (1971)~ Kies (1980), Kivic and Walne (1984), Leedale (1970)~ Levine {1970, 1973, 1978), Levine et al. {1980), Loeblich, Jr. (1974), Loeblich, III (1970, 1976), Loeblich and Loeblich (1983), Lore and Didier (1979), Lynn and Small (1981), Mahler (1981), Melkonian et al. (1982), Merinfeld (1981}, Mignot (1975, 1981), Mignot and Brugerolle (1982), Nanney (1980), Norris (1980), Orias {1976), Patterson (1979, 1980, 1984), Perkins (1971, 1976a,b), de Puytorac and Grain (1976), Ris and Kubai (1974), Round (1980), Schwartz and Dayhoff (1978), Seravin and Gerassimova (1978), Silva {1979, 1980), Small and Lynn {1981), Spiegel (1981), Taylor (1976a, 1979, 1980b), Trench {1981}, V i c k e r m a n and Preston (1976), Whatley (1981}, Whittle and Casselton (1975) and Wright et al. {1979}.

Finally, extraordinarily rich bibliographic sources -- to relevant protistological papers and books both 'ancient' and m o d e m - were provided particularly in the following therefore indispensable dozen references deserving of repetition here: Bold and Wynne (1978), Corliss (1978--79, 1979a), Cox {1980}, Finlay and Ochsenbein-Gattlen (1982), Margulis (1981a), Parker {1982}, Raikov

(1982), Rosowski and Parker (1971, 1982), Silva (1980) and Tappan (1980).

10. Brief Characterizations of Assemblages and Phyla

The remainder of this paper represents an annotated outline of a proposed high-level scheme of classification for the kingdom PROTISTA Haeckel, 1866. Names of the 18 supraphyletic assemblages (given in the vernacular only) and the 45 included phyla (formally presented) have already been listed in Table 5, but abbreviated diagnostic characterizations or descriptions and further perti- nent nomenclatural information are supplied on the following pages. All phyla are considered to be monophylet ic unless otherwise indicated; new data from future studies will likely necessitate some later revision, o f course.

Space restriction has required succinctness, essentially ruling out fuller treatments and much discussion of broader implications of both taxonomic and nomenclatural decisions and phylogenetic group-interrelationship considerations. With regard to each assemblage name, mention is made of the formal name from which it has been derived; with respect to names of phyla, only major (almost always junior) synonyms are given, and these wi thout authorships and dates (information often con- fusing wi thout accompanying detailed explanations or justifications). Only with rare exception are direct references to the literature made within the characterizations and the authorship-date data supplied with Latinized names for historical reasons are not to be considered literature citations. Names of ' typical ' genera are not included for various reasons, including lack of space and the obvious danger of labeling any selections as truly ' typical ' of an entire phylum.

Estimations of total number of species (through the year 1983), both contemporary and extinct, are included for general interest.

The bases or rationale for assignment of ranks to the various taxonomic groups included below, and for their juxtaposi t ion to

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neighboring taxa, have been given on preceding pages. I am painfully aware that dearth of crucial data often has inevitably necessitated an undesirable degree of speculation, a handi- cap suffered by all workers in evolutionary protistology.

Assemblage I. The RHIZOPODS Essentially the rhizopod amoebae and groups

thought to be reasonably related to them: the long and well known 'rhizopod sacrodinids' of the general, especially protozoological, literature, with modern taxonomic refinements. Characterized principally by the common possession of lobose, filose, or reticuiose pseudopodia at some stage in the life cycle or of a shuttle-type flow of cytoplasm. Mitochondria, if/ when present, generally with tubular cristae; however, one or two groups exhibit the discoidal form, and a few other species, a flattened, plate-like form. A biflagellated stage in the life cycle common but not universal. Vernacular name derived from that of class Rhizopoda yon Siebold, 1845, or from the earlier 'les Rhizopodes' Dujardin, 1835. Six or seven phyla, seventh here with considerable uncertainty, and estimated total of some 44 000 described (with possibly several thousand of them highly questionable, however?) contemporary and extinct species, with the latter representing as much as 75% of the overall number, primarily because of so many fossil ' forams. '

(1) Phylum Karyoblastea Margulis, 1974 (syns. Caryoblastea, Pelobiontida). No mitochondria, no Golgi bodies, no spindle fibers, no true flagella, perhaps no true mitosis (or chromosomes), no meiosis. Single lobose pseudopodium or protoplasmic bulge during locomotion. Lives in freshwater microaero- philic benthic habitats. Aigivorous (plus debris and sand grains). Stores glycogen. Contains xenosomes represented by at least two species of prokaryotes appearing in large numbers in cytoplasm and considered essential to life of host. Single genus, Pelo- myxa, with possibly only one valid species, P. palustris.

Nomenclatural note. Name, originally spelled with a 'C ' [here emended to a 'K ' ] , was coined and made available by Prof. G. Evelyn Hutchinson of Yale University, according to Dr. Lynn Margulis (pets. c o m m . ).

(2) Phylum Amoebozoa Liihe, 1913. Mitochon- drial cristae generally tubular, although discoidal in many members of amoeboflagellate subgroup and reported as lamellar in a few other species. Lobo- podia common, but sometimes reduced to wave-like protoplasmic bulges in locomotion. Many subgroups 'naked, ' including some important endosymbiotic

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forms, but testaceous amoebae possess tests or shells composed of chitin or glassy organic plates or sand grains (or other debris) glued together by secreted material, often in specific patterns. Amoeboflagel- lates, plus a few other forms, may possess flagella at some stage in life cycle; otherwise, basal bodies absent, as are centrioles. Reports of sexuality uncon- firmed. Species live in fresh- and salt-water habitats, with many also found in soil, and others symbiotic or parasitic in variety of host organisms. Resistant cyst important stage in life cycle of many. Nearly

5000 species described, but perhaps half (mainly testaceous forms) should be considered doubtful until redescription; some fossils known.

Nomenclatural note. ] am indebted to Georges Merinfeld (pers. comm.) for indicating both the availability and appropriateness of the (formerly class-level) name used for this group loosely represented in the literature by the bulk of the common so-called 'animal-like' (as opposed to 'fungus-like') 'rhizopod sarcodinids. '

(3) Phylum Acrasia Van Tieghem, 1880 (syn. Acrasiomycetes). Mitochondrial cristae discoidal (rarely, tubular). Amoeboid state with lobose pseudopodia typical, although a form with two flagella (of equal length) found in one species. The life cycle of these perhaps primitive 'cellular slime molds,' which occur in fresh water or damp soil and show no sexuality, of taxonomic importance: aggregation of uninucleate amoebae yields pseudo- plasmodium that, in turn, produces upright fruiting body or sorocarp (on a nontubed stalk of living cells) bearing spores (in chains) from which, under proper conditions, typically emerge unicellular amoebae capable of recommencing cycle. Only half a dozen species known.

Nomenclatural note. Name used has generally been applied at class or even subclass level, but composition of group is essentially unchanged (although some workers have included Dictyostelium and relatives -- despite their significant differences -- here rather than in following phylum).

(4) Phylum Eumycetozoa Zopf, 1885 (syns. Myxomycota p.p., Myxomycetes p.p.). Mitochondrial cristae tubular. Amoeboid forms (myxamoebae) generally with filopodia; flagella or biflagellate stage anterior and of unequal length, neither bearing flagellar hairs; common multinucleate plasmodial stage reaches length of several meters and exhibits shuttle- flow protoplasmic streaming. Life cycles made complex by superimposition of sexuality, with alternation of haploid and diploid generations: haploid organisms, often biflagellate, fuse to form diploid zygotes. Many species here comprise the 'acellular or true slime molds' because vegetative life cycles contain 'noncellular ' (i.e., syncytial, multinucleate) plasmodial stage that, in turn, can give rise to a multispored fruiting body (sporo-

carp) on a tubed stalk the cells of which have cellulose walls. Except for Dictyostelium, sporocarp much more complex than in preceding phylum. Sporangia contain uninucleate spores capable, on germination, of restarting whole cycle. For many species showing sexuality, zygotes can be formed from fusion of either myxamoebae or myxoflagellates or one of each. More than 700 species described.

Note. The exceptional Dictyostelium shows neither sexuality nor flagellated stages and is considered to be a second kind of 'cellular' slime mold by many (see preceding phylum). But I consider it to be evolutionarily further removed from the Acrasia than from other classes (prostelids, myxogastrids) of the present phylum Eumycetozoa.

(5) Phylum Plasmodiophorea Zopf, 1885. Mito- chondrial cristae tubular. Minute multinucleate plasmodia grow inside cells of hosts (terrestrial plants) following invasion by biflagellated zoospores that transform first into myxamoebae, latter developing into plasmodial stage. Pair of apically located flagella of unequal length but smooth (i.e., no hairs); in swimming, one directed backward. Sexuality reported. Infective uninucleate spores from plasmodia release zoospores; a cystic stage can survive for long periods in soil. About 35--40 species of these 'endoparasitic slime molds' described.

(6) Phylum Granuloreticulosa De Saedeleer, 1934. Mitochondriai cristae tubular. Pseudopodia, used in both food-capture and locomotion, generally reticulopodia (in anastomosing network) plus some filopodia: reinforced with microtubules not in geometric arrays. Typically with tests or shells of calcareous composition, single- or more often multichambered, perforated with innumerable pores. Sexual reproduction widely present, with gametes bi- or nonflagellated and with full life cycle often including alternation of generations. Some species exhibit nuclear dimor- phism, with somatic and generative nuclei reminiscent of condition found in phylum Ciliophora of assemblage XIV (below). All species (with few exceptions) marine, typically benthic although some planktonic, with many bearing large populations of symbiotic pigmented fellow.protists in tests and cytoplasm. More than 37 500 species described, with perhaps 80% fossilized forms (many of extinct lines); some require restudy. New 'foram' species descriptions continue to flood the specialized literature.

Note. Overwhelmingly, the major included group are the Foraminifera d'Orbigny, 1826, which some workers may wish to isolate in some way as an independent phylum.

(7) Phylum Xenophyophora Schulze, 1904. Little known protist group tentatively placed in an incertae sedis position among the rhizopods for want of better location. Marine benthic forms with multinucleate plasmodial stage enclosed in branched-tube system

composed apparently of some transparent organic substance. Barite crystals in cytoplasm. Tests of foreign materials surround tubes plus egested 'fecal pellets.' Filose or reticulose pseudopodia mentioned in some descriptions. While needing reconfirmation, biflagellate gametes and small amoeboid stages also reported as part of full life cycle of some species. Large protists, with specimens from deeper parts of ocean floor measuring up to 25 cm. Some 36 contemporary species described. Swinbanks (1982) has suggested that trace fossil Paleodietyon species (graphoglyptids) may actually represent extinct xenophyophorans.

Assemblage H. The MASTIGOMYCETES Essentially the aquatic or parasitic 'lower fungi,'

with flagellated zoospores, a group long known in the general mycological literature and approximately that of Phycomyceten de Bary, 1884, carried into the 1960's as the Phycomycetes of Sparrow (1960)and others and retained, in the vernacular, as 'the phycomycetes.' But today the term mastigomycetes (based on the formal name Mastigomycetes Moreau, 1954) seems more appropriate in view of the significance of the flagellated stages in these (otherwise) rather 'fungus-like' organisms. In fact, the heterokont condition of many of the included species suggests that the overall group may have had phylogenetic roots close to Assemblage VIII, the chromobionts. Mito- chondrial crlstae tubular in two of the groups, but distinctly flattened or plate-like in the appended third phylum (which is uncertainly related to other two). Estimated total of some 1750 described species (including perhaps 300 doubtful forms).

(1) Phylum Hyphochytridiomycota Sparrow, 1959 (syn. Hyphochytriomycetes). Mitochondrial cristae tubular. Many species with chitin in cell walls, but some with cellulose. Zoospores with single anteriorly directed flagellum, possessing tubular flagellar hairs, but additional (barren) basal body nearby. Lysine biosynthesis by diaminopimelic acid (DAP) pathway in some species, by amino-adipic (AAA) in others. Isogametes reported in some life cycles. Exhibiting osmotrophic nutrition, included species occur mainly as widespread fresh-water forms parasitic on other protists and aquatic plants. Some 25 species described.

Nomenclatural note. Variant spellings of the name for this group may be considered to fall as synonyms. Authorship-date often given as 'Sparrow, 1958,' but fascicle with the name did not appear until the following year.

(2) Phylum Oomycota Winter, 1879 (syn. Oomy- cetes). Mitochondrial cristae tubular. Cellulose in cell walls. Oospores typically release" heterokont zoospores, organisms with two unequal flagella (forward one with tubular hairs, trailing one smooth). Lysine

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biosynthesis by DAP pathway only. Mycelia coenocytic or syncytial (i.e., composed of multinucleate aseptate hyphae) and diploid. Sexuality reported, with gametes nonflagellated. Typical 'water molds,' included species are parasitic or saprobic forms occurring in fresh water or soil, with hosts ranging from potatoes and grapes to fishes. More than 800 species described, but many should be considered of doubtful validity until further studied.

(3) Phylum Chytridiomycota Sparrow, 1959 (syn. Chytridiomycetes). Placed in an incertae sedis position within this assemblage not for lack of knowledge about the group but because of its apparently rather distant relationship to members of the other two phyla. Mitochondrial cristae plate-like or lamellar, never tubular. Chitinous cell walls in hyphal stage. Most gametes and some asexual zoospores have single flagellum, posteriorly located (and projected) and smooth (i.e., no flagellar hairs). Lysine biosynthesis is by AAA pathway only. Sexuality known. Unique cytoplasmic body, the ' rumposome, ' occurs near body surface associated with other structures such as microbodies, microtubules, lipid droplets, and mitochondria. Like other mastigomycetal forms, included species occur as parasites or saprobes in soil or fresh-water habitats. Some 900 species described.

Note. Is the enigmatic marine Nephromyces (Saffo, 1981; Saffo & Nelson, 1983) assignable here or better in assemblage VIII, phylum Proteromonadea, below? Regarding 'Sparrow, 1959,' see note under first phylum, above.

Assemblage III. The CHLOROBIONTS Essentially the 'Chlorophyte Series' of the recent

phycological literature (see Christensen, 1966; Stewart and Mattox, 1980; Taylor, 1978 ; and others), predominantly the divisions or classes long known as the 'green algae,' including both flagellated and nonflagellated groups although here excluding the euglenophytes (Assemblage IV, below). Particularly united by their common possession of chlorophylls a and b (except in the glaucophytes) and flattened mitochondrial cristae. Contrast with the chromobionts (assemblage VIII, below). Undoubtedly evolutionary forerunners of the earliest members of the kingdom Plantae. In fact, some botanists now group the 'green algae' with the so-called 'higher' plants into a single very high-level assemblage, called the 'Chloro- biota, ' 'Chlorobionta, ' or 'Viridiplantae,' leaving other algal taxa (formerly also considered plants) elsewhere (e.g., see Cavalier-Smith, 1981b; Edwards, 1976). While the vernacular name chlorobiont thus suffers a bit from potential dual usage, I still consider it more appropriate as a protist designation than the term 'Chlorophyte'; furthermore, I have reserved the latter for use in reference to the first phylum of this

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group. Four or possibly five phyla (although the small fifth group, the glaucophytes, here with considerable uncertainty) and estimated total of some 9000 acceptable species (4--5% described as fossils), exclusive of perhaps an additional 5000 questionable species of desmids.

(1) Phylum Chlorophyta Pascher, 1914 (syn. Isokontae p.p.). Mitochondrial cristae plate-like or lamellar (flattened). Organisms are the 'green (or grass-green) algae,' with chlorophylls a plus b always present, as well as many carotenoid derivatives and various xanthophylls, starch as food reserve, and cellulose in cell walls (latter often encrusted with minerals). Thylakoids stacked in bands of 2--6. Uni- cellular stages, including zoospores and gametes, typically biflagellate, both anteriorly directed and without tubular hairs. Basal body transitional region shows unique 9-fold star pattern. Eyespot occurs within typically single chloroplast. Sexuality known. Diverse morphological types: unicells, coenobia, colonies, ceonocytic filaments, parenchymatous and siphonous organization {some of latter multinucleate and able to produce multiflagellate sperm cells); species of some groups have no motile stages. Some 3200 species known, predominantly from fresh- water habitats.

Nomenclatural note. Some writers might assign the authorship-data here to 'Rabenhorst, 1864,' but that early author spelled the name 'Chlorophyllophyceae' and viewed the group quite differently taxonomically.

(2) Phylum Prasinophyta Christensen, 1962 (syn. Prasinomonadea). Mitochondrial cristae lamellar, although one small group with discoidal type of flattened cristae. The 'grass-green scaly algae,' typically found as small flagellated uniceUs with one or two anteriorly located flagella, arising from a flagellar pit, often covered with scales of some sort (as are frequently the bodies as well). One benthic group multiceUular with quadriflagellate zoospores. Tri- chocysts in cytoplasm unique among green algal protists. Considered most primitive of the chlorobionts and includes some very small organisms with only one flagellum, one chloroplast, etc. Sexuality apparently rarely known. Some 350 species, with approx. 85 described as fossils, mostly from freshwater sources.

Nomenclatural note. Round (1971} was the first to recognize this group as comprising a division (=phylum), and to use the name 'Prasinophyta' for it; but it remains essentially a "Christensen group" and is so credited here.

(3) Phylum Conjugatophyta Engler, 1892 (syns. Akontae p.p., Gamophyta, Zygnematophyta). Mito- chondrial cristae lamellar. Unicellular or filamentous green algal protists with no flagellated stages in life cycle. Sexual reproduction mediated by 'conjugation' between two cells (often of appressed fila-

ments), which yields resistant diploid zygospore. Chloroplasts large and complex; in the essentially mirror-image unicellular desmids, a pair of such plastids are joined at an isthmus containing the single shared nucleus. All species fresh-water forms, their cellulosic cell walls often slimy on outside; desmids glide on such secreted mucilage. There may be nearly 5000 valid species {>80% desmids), with an additional 5000 or even more desmids with taxonomic validity uncertain until restudied; fossils rare.

(4) Phylum Charophyta Rabenhorst, 1863. Mito- chondrial cristae lameilar. Known as 'stoneworts ' and considered plants, many species are macroscopic with very large cells; multicellular in organization, they may form rhizoids, 'stems,' and 'branches.' In exhibiting sexuality, these macroalgae produce oogonia and flagellated antherozoids. Vegetative stage haploid; meiosis zygotic. Cytokinesis involves a phragmoplast (as in plants). Cellulose-containing cell walls may also be heavily calcified. Mostly fresh-water forms, some 400 species described, with approx. 300 of them as fossils.

(5) Phylum(?) Glaucophyta Bohlin, 1901 (syn. Glaucophyceae). Placed tentatively in this assemblage and/but in an incertae sedis position with respect to many considerations: rank, composition, exact characterization, and relationship to other chlorobionts. Mitochondrial cristae lamellar; chloroplasts replaced, in effect, by distinctive cyanelles of presumably cyanobacterial evolutionary origin. Some species with ventral or apical furrow; all(?) have cellulose in cell wall. Of several genera possibly assignable here (but principal characteristic held in common is presence of cyanelles as cytoplasmic xenosomes?), some have two anterior flagella (without tubular hairs) and curious pellicular alveoli reminiscent of dinoflagellates and ciliates. But two others have no flagella (reminiscent of red algae) and, in one case, no pellicular alveoli. Lysine biosynthesis by DAP pathway reported for one species. No sexuality described. Of the dozen or so species sometimes grouped under 'Glaucophyceae, ' all live in fresh-water habitats. Genera possibly involved include Cyanidium, Cyanophora, Glauco- cystis, Glaucosphaera, and Gloeochaete.

Assemblage IV. The EUGLENOZOA Composed of two major subdivisions (euglenoids

or euglenophytes of the protozoological and phycological literature plus kinetoplastids or trypanosomes and relatives of the protozoological and parasitological literature) and perhaps an additional very small one, the several species of the long recognized 'gymnostome ciliate' (now known to be a flagellate) genus Stephanopogon. Thus it contains both phototrophic (chlorophylls a plus b) 'algal' forms (Leedale, 1967) and nonpigmented mainly parasitic 'protozoan' organisms (latter first given independent taxonomic

status by Honigberg, 1963b; also see Vickerman, 1976), not to mention a free-living, marine, benthic ciliate-turned-flagellate (Corliss and Lipscomb, 1982; Lipscomb and Corliss, 1982). Included species united principally by common possession of discoidal mitochondrial cristae, sheets of cortical microtubules, cytochrome c similarities, 5S rRNA homologies, and paraflagellar or paraxial rods (although cytochrome c and rRNA data not yet available for Stephanopogon and no rods present in its flagella). Vernacular name derived from that of recently erected kingdom Euglenozoa (Cavalier-Smith, 1981). Two or three phyla -- inclusion of third remaining speculative until more comparative data available -- and estimated total of some 1600 acceptable species.

Nomenclatural note. While having the disadvan- tages of being so new that it is little known and of unjustifiably implying an animal or 'zoological' relationship, the vernacular name euglenozoa has an advantage over 'euglenoids' (my choice before Cavalier-Smith's work was published) and 'euglenophytes' in that the term is more easily separable from the older connotations of 'Euglena plus close (algal) relatives,' 'algae,' and 'phytoflagellates.' Furthermore, it renders unnecessary my composing an appropriate altogether different new name: a difficult task, to nomenclaturally embrace such formerly widely separated groups of organisms under a single 'neutral ' descriptive term. And reduction of Cavalier-Smith's (1981b) well meant name to synonymy so soon would only confound nomenclatural matters still more, an action to be avoided whenever possible.

(1) Phylum Euglenophyta Pascher, 1931 (syns. Euglenoidina, Euglenida). Mitochondrial cristae discoidal (i.e., flattened with narrow-necked base, resembling ping-pong paddle in full-face view). Chloroplasts (when present) enclosed in three envelope-membranes; chlorophylls a plus b and accessory pigments; paramylon storage granules, no starch. Distinctive pellicle (no cellulosic cell wall), underlain with sheet of cortical microtubules. Mucocysts abundant. One or two, occasionally up to four, anterior flagella (arising from depression in pellicle) with single row of nontubular unilateral flagellar hairs and, internally, a paraxial rod parallel to axoneme. Structureless basal body transitional zone. Large endosome in nucleus; mitosis closed, with intranuclear spindle. Stigma, when present, free of chloroplast and lying opposite unique para- crystalline paraflagellar body. Cytostome present, active in phagoeytosis in many nonpigmented species. No sexuality reported. Lysine synthesis by AAA pathway. More than 1000 species described, mainly free-living fresh-water forms.

(2) Phylum Kinetoplastidea Honigberg, 1963 (syns. Bodonophyceae plus Trypanosomatophy- ceae). Mitoehondrial cristae discoidal in single large

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mitochondrion that contains very large concentration of fibrillar DNA recognized as distinctive and unique organelle, the kinetoplast. No plastids. Pellicle underlain with sheet of cortical microtubules. One or two, or no, flagella arising from pocket in pellicle; when two, both bear fine nontubular hairs; a paraxial rod always present. Two basal bodies, even when only one emergent flagellum (latter typically associated with a cytoplasmic undulating membrane), linked by a desmose. Large endosome in nucleus; mitosis closed, with intranuclear spindle. No sexuality conclusively demon- strated. Lysine synthesis by DAP pathway. Nearly 600 species described, mostly as parasitic blood forms (trypanosomes) from great variety of hosts (including insect vectors), although some (leish- manias) infect other animal tissues or plants, and a sizable group (bodonids) also includes free-living biflagellate (one forward, one trailing) species from both fresh- and salt-water habitats.

(3) Phylum Pseudociliata Corliss and Lipscomb, 1982 (syn. Stephanopogonida). Placed tentatively in this assemblage in an incertae sedis position until more comparative studies can be carried out. Mitochondrial cristae discoidal. Pellicle underlain with sheet of cortical microtubules. No plastids; no kinetoplast. Mucocysts abundant. Flagella occur in several rows on body, but sparse; no paraxial or paraflagellar rod. Basal bodies connected by a desmose; structureless basal body transitional zone. Nuclei multiple (2--16) but all of same kind (homo- karyotic) and with large endosome; mitosis closed, with intranuclear spindle. Polar cytostome-cytopharynx supported by complex nematodesmata; species feed on bacteria, diatoms, small flagellates. No sexuality reported. Reproduction within cyst by kind ~)f palintomy. Four species in a single genus Stephanopogon described, small marine benthic forms formerly recognized as 'gymnostome ciliates.'

Assemblage V. The RHODOPHYTES The 'red algae' of the literature, highly distinctive

group of mostly marine protists with unknown affinities with other protist groups. Set apart principally by lack of centrioles and any flagellated stage in life cycle and by presence of single thylakoids in plastids and phycobilins as accessory photosynthetic pigments. Mitochondria with flattened cristae. Ver- nacular name derived from long-standing algal group names commencing with 'Rhodo-': Rhodophyta Wettstein, 1901, or Rhodophyceae Rabenhorst, 1863, or possibly even Rhodophyceae Ruprecht, 1850 or 1851). Single phylum (although some workers append the glaucophytes: see Assemblage III, above), and estimated total of some 5000 acceptable species (approx. 15% described from fossilized material).

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(1) Phylum Rhodophyta Rabenhorst, 1863. Mito- chondrial cristae plate-like, lamellar. Plastids, containing chlorophyll a plus phycobiliproteins (bluish and reddish pigments) and sometimes some carotenes and xanthophylis, enclosed in two envelope-membranes; thylakoids single; 'floridean starch,' product of photosynthesis, stored in cytoplasm. No flagella, no basal bodies, no centrioles; sexuality in some, but sperm nonflageUated; zygotic meiosis. Spores in some life cycles. Cell walls composed of microfibrils and considerable gelatinous material (including agar); species encrusted with CaCO 3 fossilize well. Lysine biosynthesis by DAP pathway. Practically all marine, these macroalgae exhibit body constructions ranging from unicells and filamentous forms to a more complex multicellular parenchymatous organization, with some of latter forms reaching lengths of meter or greater. Some 5000 included species of these 'seaweeds,' with approx. 750 described as fossils.

Assemblage VI. The CRYPTOMONADS The cryptophyceans or cryptomonads of the

phycological and protozoological literature, a small group of mostly pigmented (chlorophylls a and c), biflagellate, monadoid 'protozoalgal ' forms sometimes attached or assigned in the past to the taxon of dinoflagellates (assemblage XIII, ~below). Mitochon- dria with flattened cristae. Vernacular name derived from such formal taxonomic names as Cryptomon- adineae Engler, 1910, Cryptomonadida Senn, 1910, or even Cryptomonadina Ehrenberg, 1838, with full knowledge of the considerably lower rank accorded the group in the past. Single phylum of assorted forms, often little "known and of unclear relationships, and estimated total of some 200 acceptable species.

(1) Phylum Cryptophyta Pascher, 1914. Mitochon- drial cristae lamellar, flattened. Typically biflagellate (occasionally one lost), with both flagella inserted at base of distinct gullet and bearing tubular hairs. Plastids contain chlorophylls a plus c2, some carotenes (though lacking ~3-carotene) and xanthop~!ylls, and especially phycobilin pigments (inside paired thylakoids). Plastid endoplasmic reticulum surrounds plastids plus cytoplasmic starch-producing centers and so-called 'nucleomorphs.' Unique ejectisomes as extrusomes; no cell walls; internal cortical plates in some. Mitosis open, no centrioles; no sexuality known. Mode of fission atypical of algal protists. Many exhibit phagotrophy. Some 200 species described, from both fresh-water and marine habitats.

Assemblage VII. The CHOANOFLAGELLATES The unicellular or colonial protozoan 'collar'

flagellates (=essentially the mostly nonpigmented craspedomonad algae) of the literature. Stalked or embedded in gelatinous matrix, sometimes loricate,

with single flagellum per zooid and flattened mitochondrial cristae. Vernacular name derived from order Choanoflagellata Kent, 1880. Still speculative whether or not group served as direct ancestor of present-day sponges. Single phylum and estimated total of some 140 acceptable species.

(1) Phylum Choanoflagellata Kent, 1880 (syn. Craspedomonadophyceae). Mitochondrial cristae flat, plate-like. Unique collar surrounding single anteriorly projecting flagellum composed of ring of filopodia or tentacular microvilli (containing no reinforcing microtubules) and used in filter-feeding. Flagellum without tubular hairs, tapered, and retractable. Unicellular species often have microtubular cytoskeleton and, additionally, extracellular basket-like lorica strength- ened by siliceous ribs or spicules (=costae). Some 140 species, rarely pigmented, often solitary (though some colonial in organization), either stalked or free-swimming, with or without lorica.

Assemblage VIII. The CHROMOBIONTS Essentially the 'Chromophyte Series' of the recent

phycological literature (see Christensen, 1966; Taylor, 1978; and other works), predominantly what have long been known as the 'golden-brown algae' plus the 'yellow-green algae,' including both flagellated (heterokont condition typical) and nonflagellated groups. Particularly united by widespread possession of chlorophylls a and c, tubular mitochondrial cristae, and heterokont flagella [in cases of most of the flagellated species, which predomi- nate: see the vast phycological literature on the 'heterokont algae,' dating both before and since Pascher's (1937--39), classical monograph] with tubular flagellar hairs on the anteriorly projecting flagellum. Contrasted with the chlorobionts (Assem- blage III, above). Vernacular name derived from (prefix of) well established botanical names in the literature, most recently division Chromophyta Bourrelly, 1957. Formal term 'Chromobionta ' (or 'Chromobiota ' ) has occasionally appeared in recent papers; 'Ochrobionta ' has been considered (e.g., by Edwards, 1976) as synonym of 'Chromobionta ' sensu lato to indicate a botanical kingdom that would also embrace cryptomonads and dinoflagellates and stand in contrast to a second 'plant ' kingdom, the 'Chlorobionta' sensu lato. The appeal- ing and widely employed vernacular term 'hetero- konts' (based on Heterokontae Luther, 1899), referring to presence of pair of very dissimilar flagella, is not used here primarily because of lack of universality of that condition in members of all included taxa (although secondary loss often an explanation?) and because of its exhibition in species of several groups assigned to other assemblages (e.g., Assem- blages II and IX); also, certain authorities have limited the term to the xanthophytes only. Some

workers separate out the macroalgal group of brown algae (Phaeophyta), primarily because of their unique (i.e., among protists) development of differentiated cell-types (called tissues by some botanists). Six or possibly seven phyla, with seventh uncertain as to location (better in Assemblage X, below?), plus three additional, probably subphyletic, groups problematic as to their exact assignment within this assemblage; and estimated total of nearly 30 000 acceptable species (slightly >50% described as fossils), exclusive of additional 50 000--75 000(!) questionable diatoms.

(1) Phylum Chrysophyta Pascher, 1914. Mitochon- drial cristae tubular. The 'golden-brown algae,' with chlorophylls a plus c (c, +' c~ ) always present, as well as certain carotenes and xanthophylls, chrysolamin- arin (ieucosin) and fats as storage products, and typically no cell walls but often with large siliceous scales covering body. Characteristically, pair of heterokont flagella, one projecting anteriorly and bearing thick tubular flagellar hairs, other coursing posteriorly and smooth. Basal body transitional region with unique helix. Eyespot, when present, within chloroplast; plastids generally in pairs, with thylakoids stacked in threes. Sexuality rare. Some species produce delicate Ioricae; others, complex siliceous endoskeleton. Latter include silicoflagellates, marine uniflagellate forms often found as fossils. Many fresh-water species form complex cyst or stato- spore as distinctive resting stage in life cycle. Diverse morphological types: unicellular (some amoeboid), colonies, multicellular filaments; some nonmotile, some in loricae. About 850 species described, with > 200 as fossils.

(2) Phylum Haptophyta Christensen, 1962 (syn. Prymnesiophyta). Mitochondrial cristae tubular. Pig- mentation as in preceding phylum, along with several other shared characteristics. But both flagella project anteriorly and neither bears tubular hairs; further, a most distinctive feature is a coiled, filiform appen- dage containing 6--7 singlet microtubules, the haptonema, located between the two flagella. Basal body transitional zone lacks helical configuration. Paramylon as storage product. Silica never present; but organic scales and/or coccoliths, formed within cytoplasm, often come to adorn body (and even flagellar) surfaces, latter responsible for large part of today's chalk deposits. In fact, coccolithophorids comprise majority of species assignable here. Some 450 living and 1100 fossil forms known for entire phylum.

(3) Phylum Bacillariophyta Engler and Gild, 1924 (syn. D&tomea). Mitochondrial cristae tubular; and various other general characteristics, including pigmentation, essentially same as in first phylum (see above). Common vegetative stage in nonflagellated unicellular organism, with some species having uni-

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flagellate male gamete cells; flagellum single, bearing tubular hairs, but second (barren) basal body present. Colonial organization exhibited by some groups. Most distinctive character is the readUy fossilizable frustule, the cell wall in form of elaborate silica box of varied shape, with diverse ornamentation patterns exploited in comparative taxonomic considerations; in fission, half of the 'box' or bivalved test goes to each filial organism. Primarily marine planktonic forms, widespread and numerous; recorded species said to number between 50000 and 100000(!); conservative estimate of valid species is 10 000 living and 15 000 fossil forms.

Nomenclatural note. 'Diatomea' (spelled in various ways) is a much older name for this overall group, the diatoms, but one never widely accepted by botanists during the past 50 years.

(4) Phylum Xanthophyta Allorge in Fritsch, 1935 (syns. Heterokontae p.p., Tribophyceae). Mitochon- drial cristae tubular; and various other general characteristics, including pigmentation, essentially same as in first phylum (see above). The 'yellow-green algae,' commonly with two flagella (occasionally more) of typical heterokont kind: forward one with tubular hairs, trailing one smooth. Cellulose in walls, which are commonly composed of two halves, and often scales on outside of body. Paramylon as storage product. Gametes and zoospores typically biflagellate, but some of latter amoeboid. Many forms multicellular (filamentous) in organization, with muddy fresh- water habitats most common. Some 650 species described.

(5) Phylum Eustigmatophyta Hibberd and Leedale, 1970. Mitochondrial cristae tubular. Some striking differences from immediately preceding phyla: no chlorophyll c; distinctive eyespot, occurring at anterior end of zoospores and completely independent of single chloroplast; also, usually but single flagellum, forward-projected and bearing tubular hairs; and glucose stored outside plastid in unique pyrenoid body present only in vegetative stage (Golgi bodies also only in vegetative cell). Only 10--12 species described, mostly from fresh-water habitats.

Nomenclatural note. I see no compelling reason for withholding authorship from the original des- cribers, Hibberd and Leedale (1970) -- and assigning it instead to 'Hibberd, 1 9 8 1 ' - despite arguments made by Hibberd (1981) himself for such an emenda- tion, based on very strict interpretation of the rules.

(6) Phylum Phaeophyta Kjellman, 1891 (syns. Fucophyceae, Melanophyceae). Mitochondrial cristae tubular. Pigmentation and various other characters not unlike those of the first phylum (Chrysophyta, above), although prominent carotenoid derivative here is the xanthophyll fucoxanthin and the stored carbohydrate food reserve is laminarin. Both zoospores and sperm biflagellate, with display of typical

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heterokont conditon (although both flagella are laterally or subapically inserted). 'Sporophyte' (diploid) and 'gametophyte' (haploid) generations identifiable. Highly unique or at least 'key' features include organization (multicellular, filamentous or thalloid, with diverse and well differentiated 'cell types' called 'tissues' by some workers) and size: these brown seaweeds or kelp are macroalgae that can reach length, in their typically inter- or subtidal marine habitats, of up to 60 m (thus giants among protists). Some 1600 species described, few as fossils.

(7) Phylum(?) Proteromonadea Grassd in GrassY, 1952 (syns. Proterozoa p.p.; perhaps Protomastigida p.p. and Protomonadina p.p. auctt.). Placed here tentatively and/but in an incertae sedis position with respect to many considerations: rank, composition, exact characterization, and relationship to other phyla within this and other assemblages. Might all or part of the group be better attached to Assemblage X (polymastigotes, below)? Does it very likely represent a polyphyletic 'hodge-podge' group of organisms (see Nomenclatural note, below)? Mitochondrial cristae tubular in some, discoidal(?) in others; possibly no mitochondrion in one genus. All species nonphotosynthetic. One or two pairs of anisokont flagella without hairs (although tubular somatonemes on cell surface of body in some species may represent forerunner of tubular flagellar hairs of chromobionts sensu lato?). Helical pattern noted in basal body transitional zone. Flagellar scales found on certain species. Glycogen as stored food reserve. Unicellular and colonial forms known; fresh-water, marine, and parasitic (symbiotic) species described. Genera possibly involved include: Apusomonas, Cercomonas, Cladomonas, Cochlosoma, Colponema, Cyathobodo, Gyromitus, Isonema, Karotomorpha, Nephro- myces(?), Phalansterium, Proteromonas, Pseudoden- dromonas, Reckertia, Rhipidodendron, and Spon- gomonas (and still other genera?). More than two dozen likely valid species are assignable to these genera -- perhaps double that number if/when Cer- comonas species are restudied and all placed here.

Nomenclatural note. Grass6's (1952) group was actually restricted to two parasitic genera Proter- omonas and Karotomorpha, bi- and quadriflagellate forms, respectively; Vickerman (1976)has essentially agreed with such disposition, However, most of the other genera are then left homeless. While some might be apochlorotic 'chrysophytes' sensu lato, many have long been assigned to the so-called 'lower zooflageUates' alongside the choanoflagellates (Assemblage VII, above) or such genera as Bodo and Trypanosoma (now in Assemblage IV, above), places where the present forms definitely do not belong. The enigmatic Nephromyces (see Saffo, 1981; Saffo and Nelson, 1983) [better in Assemblage II, phylum Chytridiomycota, above? ] and Isonema (see Schuster

et al., 1968) only exacerbate the problem. Perhaps solely Karotomorpha and Proteromonas can (should) be removed to Assemblage X, leaving all others here (but still of highly questionable phylogenetic place- ment)? Hibberd's (1984) very recent suggestion of a series of separate 'zooflagellate orders' to accommodate a number of the unlike genera listed above is com- mendable: but in what protist phylum or even assemblage should such orders be placed, if they are at all interrelated at highest taxonomic levels?

(1) Group Bicosoecidea Grassd and Deflandre in Grassd, 1952. Appended here but in an incertae sedis position especially as to rank and phylogenetic closeness to other groups comprising chromobionts overall. Mitochondrial cristae tubular. Two flagella, arising in anterior depression of body, with longer anteriorly projecting one with tubular hairs, other smooth and anchors organism to inside base of secreted test or cup-shaped lorica. Small phagotrophic, nonpigmented forms, sometimes organized into colonies. Some 30--40 species, from both fresh- water and marine habitats, generally assigned in past to 'chrysomonads' (first phylum, Chrysophyta, above).

Nomenclatural note. Many variants of the spelling of this group-name exist; I believe the one used above is the (most) correct, thus all others may be considered to fall as synonyms [actually, the name was originally spelled 'Bicoecidea' in Grass6 (1952), emended here by insertion of the '-so-,' but still credited to Grass6 and Deflandre].

(2) Group Heterochloridea Pascher, 1912. Appen- ded here but in an incertae sedis position with regard to rank and exact location. Mitochondrial cristae tubular. Yellow-green plastids reminiscent of xanthophytes (see above), but unequal flagella and other features indicate closer chrysophyte (also see above) affinities. Storage products oil and possibly chrysol- aminarin. Some 15 species, all fresh-water forms and unicellular in organization.

(3) Group Raphidophyceae Chadefaud, 1950 (syns. Chloromonadida, Chloromonadophyceae). Appended here but in an incertae sedis position with regard to rank and exact location. Mitochondrial cristae tubular. Commonly numerous yellow-green plastids, but also a few nonpigmented species. No eyespot. Usual heterokont flagella, so characteristic of chromobionts in general. Mucocysts present. Storage product fat or oil. Golgi bodies in ring at anterior end of body. Sexuality reported. Some 27 species described, from both fresh-water and marine habitats, assigned in past to either Chrysophyta or Xanthophyta (above).

Assemblage IX. The LABYRINTHOMORPHS Nonpigmented organisms with unique membrane-

bound extracellular network by/on which movement

of spindle-shaped non-amoeboid cells occurs; known zoospores biflagellate, and mitochondrial cristae tubular. Often called 'net slime molds,' and claimed as fungi or 'lower' fungi by mycologists and as unique taxon of rhizopod amoebae by many protozoologists; long taxonomically enigmatic (e.g., see review by Pokorny, 1967). Vernacular name derived from recently proposed phylum-level name Labyrintho- morpha Page in Levine et al. (1980). Perhaps two phyla (still debatable whether or not they should be consolidated into one, which could then be known by Page's name) and total of some 36 described species (but all acceptable?).

(1) Phylum Labyrinthulea Cienkowski, 1867. Mitochondrial cristae tubular. Nonphotosynthetic forms, but minute zoospores often exhibit heterokont flagellar condition: anterior flagellum with tubular hairs, trailing posterior one smooth. Two species show orange-colored eyespots. Vegetative or trophic stage represented by unique network of spindle-shaped cells moving in slime channels, movement aided by unusual cytoplasmic organelles [formerly called sagen(ogen)etosomes, now bothro- somes]. Thin flat scales in cell walls. Cystic stage seen. Sexuality known. Lysine biosynthesis by DAP pathway. Found in abundance on certain algae and grasses (e.g., parasitic on eel-grass) in marine and occasionally brackish or fresh-water habitats. Some eight species described.

(2) Phylum(?) Thraustochytriacea Sparrow, 1943. Mitochondrial cristae tubular, species all without chloroplasts, walls with scales, and small zoospores with heterokont flagella -- characters shared, along with habitat, with members of preceding phylum to which present group thus should perhaps be/remain attached at subphyletic rank? Differences may exist with respect to rRNA and other molecular properties, in shape of trophic cells (oval or round and not in channels), lack of sexuality, and in mode of attachment to host tissue, but controversial whether such features clearly support separation at high level of phylum (see Gaertner, 1972; Olive, 1975; Porter, 1974). Some 28 species described,

Assemblage X. The POL YMASTIGOTES Essentially the 'higher zooflagellates' of the proto-

zoological literature; nonpigmented, largely endosymbiotic forms, with insects and vertebrates most commonly serving as hosts (e.g., see Brugerolle, 1977; Honingberg, 1963a). Colorless 'monads ' (better 'poly- monads'?) with flagella and mastigont systems often numbering more than two, sometimes many, per organism. Mitochondria totally absent. Vernacular name derived from such earlier names usually employed for more restricted groups and at infraclass ranks) as Polymastigina Biitschli, 1884, Polymastigina Blochmann, 1895 and Polymastigida Calkins, 1901.

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[Term seems apt for phyla I've assigned to it, unless the uncertain phylum Proteromonadea (hardly poly- monadoid in nature, although possibly ancestral to such a condition; another difference is the presence of mitochondria, with tubular cristae, in proteromonads) is placed here instead of within Assemblage VIII (above)]. Two certain phyla, plus possibly the Pro- teromonadea (see immediately above), and estimated total of some 750--800 described species, with perhaps only 550--600 acceptable as valid [the figure of 2200 inadvertently given in Corliss (1982b) was grossly in error].

(1) Phylum Metamonadea Grassd in GrassY, 1952 (syns. Hexamitophyceae plus Trichomonadophyceae p.p.). No mitochondria, no plastids. Glycogen stored, and hydrogenosomes present in cytoplasm. One or more (occasionally many) karyomastigonts, each usually with one or two pairs of flagella, with one flagellum at least (of each karyomastigont) turned back as trailing or recurrent flagellum. All flagella smooth (i.e., without hairs). Microtubules abundant: some pellicular in location, others forming rootlets from basal bodies and running as bundles deeper into cytoplasm. One major group of species has axostyle, often motile, composed of thick ribbon of microtubules. Centric intranuclear spindle involved in mitosis. Cysts and some sexuality known. Most species phagotrophic and endosymbiotic, many occurring in insects (some xylophagous), but also in other hosts including humans. Enigmatic phylum(?) Proteromonadea (see Assemblage VIII and discussion directly above) -- or at least part of it -- may belong here, which would necessitate some revision in characterization of present group overall. Estimates for total number of species vary depending on included families and validity of forms described: Vickerman (in Parker, 1982) suggests approx. 200 as valid; perhaps as many as 300 total (especially if some proteromonads included here), described, although many needing redescription.

(2) Phylum Parabssalia Honigberg, 1973 (syn. Trichomonadophyceae p.p.). No mitochondria, no plastids. Glycogen stored, and hydrogenosomes present in cytoplasm. Typically, karyomastigonts with 4--6 (sometimes 16) flagella [number occasionally much larger: one case, 340 separate mastigonts each with pair of flagella!] or akaryomastigonts with up to tens of thousands of flagella yet single nucleus; occasionally single or, one case (Dientamoeba, formerly classified as an amoebozoon, in Assemblage I), no flagellum. In one major group, recurrent flagellum common, often associated with somatic undulating membrane and underlying costa. No flagellar hairs. In all species, kinetosomes (i.e., blepharoplast- complex) are in arrangement with associated microtubular organelles uniquely characteristic of this phylum. Parabasal body (i.e., Golgi apparatus plus

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basal body-associated filament) also unique. Axo- style(s) typically noncontractile, often associated with other organeUes, including pelta. Centric extranuclear spindle in mitosis; elaborate centriolar structures, called atractophores, in one group in which also chromosomes few and very large. Cysts and sexuality known. Some groups phagotrophic, nearly all endosymbiotic; xylophagous in insects (i.e., termites and wood-feeding roaches), and some of veterinary or medical importance as parasites of vertebrates. Episymbiotic spirochaetes common on some species. About 350 valid species comprise the two major included groups (trichomonads and hypermastigotes), although larger number has been described.

Assemblage XI. The P A R A F L A G E L L A T E S The 'opalinids' of the literature (see review by

Corliss, 1~55), a taxonomically controversial astomatous group long considered primitive ciliophorans ('protociliates') on the basis of superficial similarity to ciliates, their bodies typically covered with numerous short flagella arranged in longitudinal (actually diagonal) rows. But characteristics are mainly those of flagellates: single kind of nucleus, production of gametes (and exhibition of syngamy), symmetrogenic mode of division, etc. Mitochondrial cristae tubular. Vernacular name derived from the class Paraflagellata Corliss, 1962, which was preceded by proposed supraordinal name ParaflageUida Corliss, 1955, appropriate names (and concept) for those times -- and perhaps since? -- although generally overlooked by protozoologists during past 20--30 years. 'Opalinids' is reserved for (the vernacular name of) a lower taxon within the phylum; and 'protociliates,' based on the former, now totally rejected, ciliate subclass Protociliata Metcalf, 1918, would be very misleading (and misconceptual) term to use. Single phylum and estimated total of some 200-- 250 acceptable species (although double that number described in the sometimes uncritical literature on opalinid taxonomy).

(1) Phylum Opalinata Wenyon, 1926 (syn. Proto- ciliata). Mitochondrial cristae tubular. Typically, heavy covering of short flagella arranged in diagonal rows, in vegetative stage, with two to many homo- karyotic nuclei. Haploid uninucleate (but multiflagellate) anisogametes fuse in syngamy; diploid zygote yields diploid vegetative or trophic stage (so meiotic reduction in gametes). All species nonpigmented and astomatous, feeding by pinocytosis and diffusion. Nuclear divisions acentric; cytoplasmic division basically symmetrogenic and interkinetal, with unique falx bisected. Pellicle in folds supported by microtubules. Cysts and palintomy described. Species, numbering some 400 of which perhaps only 50% valid and acceptable, occur as endosymbionts of rectum or hindgut of amphibians, especially

anurans, and, less often, of certain fishes and occasional reptile.

Nomenclatural note. Variants in spelling of name may be considered synonyms; and there is no compelling reason for crediting phyletic name to more recent authors, since overall composition of group (except for increase in numbers of species) unchanged in past 75 years. 'Protociliata,' earlier but entirely inappropriate and highly misleading name, best discarded for this specialized, evolutionary 'dead-end' line of complex paraflageUates.

Assemblage XH. The ACTINOPODS The long recognized 'actinopod sarcodinids' of the

protozoological literature, with its predominantly marine species characterized by widespread possession of axopodia with microtubular cores, with many groups possessing elaborate endoskeletal systems as well. Mitochondrial cristae tubular, with possibly a few inexplicable exceptions. Vernacular name derived from class Actinopoda Calkins, 1909. Some five phyla (with first probably still in a di- or polyphyletic state with respect to evolutionary origin), and estimated total of some 11 000--12 000 described extant and extinct species (possibly half destined to be considered unacceptable by specialists, although new species descriptions, especially of fossil forms, con- tinually flood the literature), with latter representing as much as 50-60% of overall number.

(1) Phylum Heliozoa Haeckel, 1866. Mitochon- drial cristae generally tubular, but flat or plateqike in one tentatively included group (centrohelids). Radi- ating axopodia stiffened by microtubules in various arrangements. Without central capsule ; internal skeleton either absent or composed of variable number of spines siliceous or organic in nature; cytoplasm not clearly divided into two zones. Extrusomes common. Sexuality rare; but zoospores present in some species, uni- or bifiagellate, perhaps a few amoeboid. Fresh- water (mostly) or marine planktonic forms, some stalked and sessile, with approx. 175 species described (perhaps only 100 acceptable to stringent specialist).

(2) Phylum Taxopoda Fol, 1883. Mitochondrial cristae tubular. Microtubules of radiating axopodia in specific hexagonal arrays, inserting on complex nucleotheca in ball-and-socket-like articulation. Non- actin contractile fibers associated with bases of oar- like axopodia cause 'beat, ' literally rowing organism through me~lium (salt water). Siliceous spines (also) present. Small, biflagellate swarmers (zoospores?) reported. Bilaterally symmetrical, marine planktonic forms all considered assignable, to date, to single valid species, Sticholonche zanclea.

(3) Phylum Acantharia Haeckel, 1879. Mitochon- drial cristae tubular. Radiating axopodia (plus some reticulopodia?) with cores of intricately cross-linked

microtubules. Inorganic endoskeleton (strontium sulfate, celestite: highly soluble, thus rarely fossilizable) of spicules oriented precisely according to J. Miiller's Law, conjoining at center of cell. Internal central capsule, with open-meshed membrane, en- closes nuclei, inner cytoplasm, etc. Myophrisks (fibrillar myonemes) in ectoplasm. Swarmer cells with two flagella, one forward-projecting and one trailing, but no tubular flagellar hairs on either. Young tro- phont stages uninucleate, becoming multinucleate with maturity. Sexuality known. Many of these marine planktonic floating predators contain species of haptophyte algae as symbionts. Some 475 species described, with perhaps only 200 valid, and no fossil forms known.

(4) Phylum Polycystina Ehrenberg, 1839 (syn. 'Radiolaria' auctt., p.p.). Most mitochondrial cristae tubular. Radiating axopodia (plus some reticulopodia), all arising from single central axoplast, with axonemal microtubules in parallel arrangements with interlinking bridges. Endoskeleton of siliceous nature, forming lattice (in one or more concentric layers) with or without spines or spicules. Central capsule composed of heavy, massive organic plates pierced by pores and distinctly partitioning cell into inner endoplasm and outer vaeuolated ectoplasm. Biflagel- late isospores produced by some species. Bodies often filled with endosymbionts (xenosomes), zooxanthel- lae or zoochlorellae. Marine planktonic forms spherical or sometimes flattened and sometimes colonial {in common mass of jelly); usually uninucleate. Some 9750 species described, 70% as fossils, but possibly only 4800--5000 acceptable as valid. Polycystine paleontology now 'in explosive phase' (E.G. Merinfeld, pets. comm.), so numbers of fossil species will very likely continue to rise rapidly.

(5) Phylum Phaeodaria Haeckel, 1879 (syn. 'Radiolaria ' auctt., p.p.). Mitochondrial cristae tubular. Axopodia appear to arise from single sources nearer one pole of organism than other; usual core of axonemal microtubules. Endoskeleton, if present, may be of silica mixed with organic material and consists of shells (sometimes resembling two hemi- spherical valves with extensive ramifying processes) and/or of hollow spines. Central capsule with very thick double membrane with so-called astropyle (functioning as cytopharynx) at one pole and pair of smaller openings (parapylae), penetrated by axopodia, at other. Unique phaeodium, mass of apparently predigested food and dark debris, in ectoplasm near parapylae. Single huge nucleus, often with hundreds of apparently intact chromosomes. No algal endosymbionts of any kind. All unicellular, often large and of diverse form, marine planktonic. Some 1100 species described, very rarely from fossilized material, but perhaps only 650 acceptable as valid. [To specialists on 'radiolarian' groups, phaeo-

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darians are vastly different from members of all preceding phyla, although textbooks -- erroneously -- often link them very closely to the polycystines (directly above) in particular. ]

Assemblage XIII. The DINOFLAGELLATES A long known distinct yet diverse assemblage of

predominantly biflagellated organisms (commonly with one flagellum encircling the body at an equatorial level and other positioned at right angles to the first and trailing posteriorly) with unique nucleus (condensed chromosomes, etc.), cortical alveoli, and tubular mitochondrial cristae. It embraces pigmented (xanthophylls as well as chlorophylls a and b and carotene) and nonpigmented forms, phototrophic and phagotrophic species, motile and nonmotile stages, solitary and colonial species, thecate and non- thecate forms, and symbiotic, free-living, and fossil groups. Vernacular name derived from order Dino- flagellata Biitschli, 1885, although both concept and content of the group have changed with time; however, 'dinozoa' -- from Cavalier-Smith's (1981b) formally named phylum D i n o z o a - seems totally unnecessary to adopt, unlike the situation for the euglenozoa (see Assemblage IV, above). The extrem- ely popular and clearly understandable 'dinoflagellates' remains ideal. [The old name 'cilioflagellates' is inappropriate, as perhaps are 'pyrrhophytes ' from Pyrrhophyta Pascher, 1914 (although this name, sometimes spelled 'pyrrophytes' is well known among botanists) and 'mesokaryotes' of some modern workers (e.g., see very recent paper by Herzog et al., 1984}, the latter having misleading evolutionary implications while nevertheless attrac- tively emphasizing the uniqueness of the assemblage overall. ] The several diverse phylogenetic lines within the dinoflagellates sensu lato can probably be fitted into two phyla, but more conservative workers might prefer reducing them all to just the first one named below, and a few 'splitters' might wish to raise several classes to independent phyletic status. Two phyla (with names based on what were originally family-level taxa) tentatively proposed here, then, with appended uncertain groups (at ranks below level of phylum} generally representing either poorly known ectosymbiotic forms or largely fossilized forms. Estimated total of some 4200 largely acceptable living and fossil species (exclusive of the enigmatic acritarchs: see third incertae sedis group, below), with approx 50% of each kind.

(1) Phylum Peridinea Ehrenberg, 1830 (syns. Desmokontae p.p., Dinoflagellata s.s., Dinophyta s.s., Pyrrhophyta s.s., Mesokaryota s.s., Dinophyceae plus Desmophyceae minus Syndiniophyceae). Mitochon- drial cristae tubular. Chlorophylls a plus c 2 in photosynthetic species, with certain carotenes, peridinin, and various xanthophylls; thylakoids typically in

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threes. Plastids (when present) enclosed in three envelope-membranes; starch stored in cytoplasm. Primitive members have pair of apically inserted flagella, free of body; in great majority of species they arise from mid-body location, with one trans- verse, ribbon-like, lying in equatorial annulus or girdle, with striated paraxial rod and single row of nontubular flagellar hairs and other basically longitudinal, usually lying in sulcus, with or without rod and with two rows of stiffer hairs. Body pellicle with alveoli, underlain by microtubules, in which cellulosic plates (2--many) present in numerous subgroups, forming complex theca in patterns of taxonomic usefulness. Mitosis acentric, with spindle extranuclear; nucleus ( 'dinokaryon') large, with chromosomes, often numerous, condensed, poor in histones, and attached to nuclear membrane. Some species with (simple) eyespot, and highly complex ocellus in one taxonomic subgroup. Trichocysts widespread, and unique extrusomes, nematocysts, in few specialized species. Certain members bio- luminescent; toxins produced by some groups; cysts formed by many. Majority marine planktonic forms, but also important fresh-water groups; nonpigmented phagotrophic species also numerous; both auto- and heterotrophic forms found living as symbionts on or in other organisms. Some species with catenoid or branched colonies. Sexuality not common but known, with flagellated isogametes; zygotic meiosis, with vegetative stage haploid. Thecate forms and cysts readily fossilizable, most hystrichophytes probably belong here (too): see group Acritarcha, below, for brief discussion. More than 4000 species validly described, about half as fossils.

(2) Phylum(?) Syndinea Chatton, 1920 (syns. Syndiniales, Syndiniophyceae). Mitochondrial cristae tubular. Totally nonphotosynthetic, endosymbiotic forms revealing typical dinoflagellate characters in their uninucleate, biflagellate, motile zoospore (dino- spore) stage but showing other unique features, especially in multinucleate parasitic phase. No pellicular alveoli or thecal plates, nutri t ion purely osmotrophic (saprozoic), centrioles associated with mitotic division, very low chromosome numbers (only 4--10), presence of histones easily detected, no arched whorls of chromatin fibers, and chromosomes all V-shaped with apex attached to nuclear membrane. Sexuality questionable. All species (with two possible exceptions) occur in association with only marine hosts -- other protists, certain invertebrates, eggs of some fishes -- and act as true parasites, destroying host cells or tissues. By rapid divisions, minute dinospores produced, serving as infective stage for fresh hosts. Some five or six families, with perhaps 40--50 valid species.

Note. Members of this group are not to be confused with symbiotic species belonging to various

subtaxa of the preceding phylum Peridinea. The latter typically have some combination of the following features: pigmented and]or thecate in some stage, large or very large number of chromosomes, ability to form catenoid colonies, fresh-water hosts, and/or ectoparasitic (although some are endosymbiotic, but still with one or more of the other characters listed here).

Nomenclatural note. I am in agreement with Loeblich (1976) that the taxonomic distinctiveness of these dinoflagellates should be recognized; the rank of phylum is tentatively proposed until further comparative work can be carried out.

(1) Group Ebriidea Deflandre in Grassd, 1952 (syns. Ebriacea, Ebriales, Ebriophyceae). In an incertae sedis position with respect to taxonomic rank, but very likely associable with dinoflagellates s.l. Only three acceptable extant species known, presumably with tubular mitochondrial cristae. Biflagel- late, athecate, marine planktonic forms, nonpigmented and phagotrophic. Loricate (and also cystic?) stage(s) in life cycle of some species. Dominating feature used in systematics of group is skeletal morphology, all species showing quite elaborate siliceous endoskeleton, readily fossilizable. Some 75--80 extinct species, all from marine material and practically all described by paleoprotistologist G. Deflandre.

(2) Group Ellobiophyceae Loeblich III, 1970 (syn. EUobiopsidea). In an incertae sedis position with respect to taxonomic rank, but quite likely associable with dinoflagellates s.l. Presumably with tubular mitochondrial cristae. All marine, nonphotosynthetic, ectoparasitic organisms attacking and attaching to integument of pelagic mysid mala- costracan crustaceans or (one species) certain poly- chaete annelids. Vegetative or feeding stage reminiscent of mycelial structure of certain fungi, with rhizoid-like sucker, multinuclear segments, cell walls, body sometimes branching, etc. Cleavage products of special (terminal) cell or zooid may number in hundreds, and zoospores (dipospores?) so produced are spherical, athecate, biflagellate forms serving as infective stage. No sexuality reported. Fewer than 10 species described.

(3) Group Acritarcha Evitt, 1963. Comprised totally of fossil forms, with a kind of 'skeleton' or 'cyst ' of organic composition (though often min- eralized) having pores or openings and arrays of various spines or processes, latter sometimes exhibiting quite elaborate or complex sculpturing; fossil remains seem to represent central body, test, shell, or vesicle of the once living protist. Group particularly subject to an incertae sedis treatment because it may deserve no single independent status at any taxonomic rank. Its members accorded class status by some paleobiologists (see Evitt, 1963). Formerly grouped with acritarchs were hystrichophytes

(Hystrichophyceae M~/dler, 1963, with various synonyms), now known to be fossilized cysts of peridinean dinoflagellates, with a few others assigned to the Prasinophyta (see Assemblage III, above). Remaining forms -- a residue of some 400 genera (see Tappan, 1980) -- assigned here until further study; since many of them are of some stratigraphic utility, it is important to know more about their systematics. Some ultimately may be considered fossilized cysts of species embraced by any one of several existing protist phyla, or they may belong to as yet unknown (new) phyla (extinct or extant); a few may even represent parts or stages in life cycles of organisms belonging to nonprotist kingdoms. Present group, overall, is thus very likely unnatural and polyphyletic. Attachment to dinoflagellate assemblage, though temporary, may actually turn out to be not unreasonable -- as more data become available -- for many of the species uncritically grouped here now.

Assemblage XIV. The CILIATES A very long recognized heterotrophic protozoan

group, characterized principally by universal possession of (generally) many cilia, a distinctive infraciliature, pellicular alveoli, and an essentially unique heterokaryotic (micro- and macronuclei) nuclear condition (Corliss, 1961, 1979a). Mitochondria with tubular cristae. Vernacular name derived from Ciliata auctt., with Ciliata Perty, 1852 probably first formal use of the name for these protists. From time to time, 'heterokaryotes, ' stemming from Heterokaryota Hickson, 1901, has been suggested as an informal descriptive name: while not an inappropriate term, it is not needed and does stress a magnitude of cleavage between the present assemblage and all-the- others-together that may be evolutionarily unwar- ranted. An even older, but long rejected, name is 'infusorians, ' unfortunately formally resurrected recently via the phylum Infusoria Cavalier-Smith, 1981 (see Cavalier-Smith, 1981b). Single phylum and estimated total of some 8000 acceptable species (with relatively very few described as fossils): see Corliss (1979a).

(1) Phylum Ciliophora Doflein, 1901. Mitochon- drial cristae tubular. Heterotrophic forms with heterokaryotic nuclear apparatus (diploid micro- nuclei and polyploid macronuclei), multiple cilia over body (with quite rare exception), pellicular alveoli (rarely absent), and always an infraciliature (highly developed cortical system of microtubules, microfibrils, and various specialized organelles, with kinetid as central feature). Basically homothetogenic fission, across kinetics, although reproduction may also be by budding, binary or multiple. Diploid organisms, with sexuality represented by conjugation, not syngamy, with exchange of reciprocal haploid 'gametic' nuclei,

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not gametic cells or gametes. Many species phagotrophic, possessing functional cytostome; ingestatory 'sucking tentacles' (polystomy) in one group; endosymbiotic forms often mouthless. Cilia may be simple, appearing singly in somatic rows, or may he organized into several types of so-called compound ciliary organelles (for feeding or locomotion). Many species mobile, others sedentary (often stalked, sometimes loricate); colonial forms (especially arboroid) common in some groups; life styles range from free- living and free-swimming to commensalism, sym- phoresy, or parasitism involving variety of hosts. Cysts part of many life cycles. Found in all sorts of habitats, with some major free-living marine groups, in particular, playing significant role in food chains and nutrient recycling. About 8000 acceptable species, few as fossils.

Assemblage XV. The SPOROZOA A century-old group of totally parasitic protozoan

species with or without 'spores,' mostly depending on one's definition or understanding of that term (see Corliss and Lore, 1984). It is best identified today and taxonomically set apart from the other great protist assemblages -- by a unique apical complex of specialized organelles clearly visible only by electron microscopy (Levine et al., 1980; Long, 1982). Mito- chondria (if present) with tubular cristae. Vernacular name derived from long known formal name Sporozoa Leuckart, 1879, first used at level or rank of class but including essentially same subgroups known today (Vivier, 1983). 'Apicomplexans, ' derived from rather popular phylum name Apicom- plexa Levine, 1970, and aptly descriptive, nonetheless seems unnecessary: sporozoa is a universally recognized term that need not be considered as descriptively misleading. Single phylum, the uncertain order Perkinsida appended (see data in Perkins, 1976b), and estimated total number of some 5000 generally acceptable species.

(1) Phylum Sporozoa Leuckart, 1879 (syn. Api- complexa). Mitochondrial cristae, when mitochondria present, tubular. Practically universal presence at some stage in life cycle of unique group of apically located ultrastructural organelles: polar ring(s), conoid, rhoptries, micronemes, subpellicular microtubules, and often, nearby, a micropore (sometimes more than one). All included species are symbionts, involving great variety of hosts; many are endopara- sites with polymorphism (including resista'nt stages) exhibited and multiple hosts required in full life cycle. Stages may involve asexual reproduction (schizogonic s.l) phenomena known as merogony, gametogony, and sporogony; sexual reproduction is by syngamy, often with anisogamous gametes; commonly zygotic meiosis. Flagella (one to three) occur only on microgametes of some species, and are

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without hairs; pseudopodia (when present) essentially limited to use in feeding, not locomotion, and not widely found. Basal bodies of flagella, and centrioles (although rarely found), presumably possess nine singlet microtubules in their composition, rather than the otherwise universal triplet condition found in other protists and in members of the plant and animal kingdoms. About 5000 species acceptably described, some of very small size (e.g., the intracellular malarial parasites of such medical importance, with associated hosts from all possible kinds of environments -- terrestrial, edaphic, aquatic (marine, brackish, fresh-water habitats) -- and representing all major animal and several other protist groups.

(1) Group Perkinsida Levine, 1978. Single included species, Perkinsus marinus, pathogenic parasite of oysters, placed in separate order and/but in an incertae sedis position with respect to definite inclusion in preceding phylum, or elsewhere, until data on it become available in greater quantity. Mitochondrial cristae appear to be tubular. The organism's conoid forms incomplete cone; and other features of typical sporozoan apical complex sometimes not altogether clear-cut (and some might be result of convergent evolution?). One or two micropores present. Free- living migratory 'zoospores' (for transfer to fresh host) have pair of flagella, one arising anteriorly and bearing row of fine hairs, other posterior and smooth; basal bodies (and centrioles) have microtubules in triplets. No cysts or resistant spores. One host in life cycle, and no sexuality known; now found in Pacific as well as Atlantic bivalve molluscs. Some workers suggest possible affinities for this enigmatic protist species with proteromonadeans, a flagellate group itself of uncertain assignment (see Assemblages VIII and X, above).

Assemblage XVI. The MICROSPORIDIA A sizable group of minute intraceUular parasites

(with wide taxonomic range of hosts, although most are insects or fishes) possessing resistant unicellular spores characterized by presence of single polar filament or tube. No mitochondria and no flagellated forms in any stage of life cycle. Vernacular name derived from formal name Microsporidia Balbiana, 1882, first used at the rank or level of order but including essentially same basic subgroups known today. 'Microsporans', derived from recently proposed subphylum [later phylum]. Microspora Sprague, 1969, is unnecessary name. Single phylum and estimated total number of some 800 acceptable species.

(1) Phylum Microsporidia Balbiani, 1882 (syn. Microspora). No mitochondria, no plastids, no flagella. Minute intracellular parasites possessing unique unicellular spores in life cycle, with single eversible polar tube through which infective sporoplasm

extruded and inoculated into fresh host tissue or ceil. Entire extrusion apparatus, largely derived from prominent Golgi apparatus and with several components often quite complex, fills most of cavity of spore. Variations in parts of extrusion system, in shape of spore, and in sculpturing of latter's outer proteinaceous exospore wall of taxonomic usefulness. One layer of wall with chitin. On entering appropriate cell, sporoplasm may develop into multinucleate plasmodiai stages eventually leading to sporulation of new generation of spores. Pathogenic in many hosts, particularly of widespread occurrence in various insect groups, crustaceans, and certain fishes; found also as parasites of other protists. Sexuality unknown. Some 800 described species considered valid by specialists.

Assemblage XVII. The HAPLOSPORIDIA A small group of forms endoparasitic in inverte-

brates and ' lower' vertebrates with spores that contain no polar filaments or tubes. Mitochondrial cristae apparently flat. Vernacular name derived from formal name Haplosporidia Caullery and Mesnil, 1899, first used at rank or level of order but including essentially same kinds of species known today. 'Ascetosporans, ' based on recently proposed phylum Ascetospora Sprague, 1979 [ 'asceto-' suggested as replacement for 'haplo-' purely to avoid implication of 'simple'], is an unnecessary name. Single phylum, with affinities of certain of the sometimes included subgroups still unclear (also see Assemblage XVIII, below), and estimated total number of perhaps only some 25 acceptable species at most.

(1) Phylum Haplosporidia Caullery and Mesnil, 1899 (syns. Aplosporidia, Ascetospora p.p., Balano- sporida). If mitochondria present, cristae may be predicted to be flattened, lamellar. Spores may be complex (including exospore with long 'tails' or projections) and may have multicellular origin in development. Sporoplasm with enigmatic structures (virus-like xenosomes or packets of lytic enzymes?) called haplosporosomes. No polar capsule, no polar filament. Infective sporoplasm emerges, at appropriate time, through orifice in spore walls usually closed by externally hinged cover (operculum) or by internal flap (diaphragm). All species parasitic in cells or tissues of primarily marine molluscs and annelids or of trematode helminths themselves parasitic in marine molluscs and decapod crustaceans; occasional hosts include tunicates and fresh-water oligochaete annelids. About 25 acceptable species described.

Nomenclatural note. Several groups included by Sprague (his latest classification: Sprague, 1982) are transferred, in an appended incertae sedis position, to the following assemblage (see below), serving as another reason to adopt the older, time-honored name Haplosporidia for the present phylum. Inci-

dentally, the original spelling of the name, in 1899, was 'Aplosporidies. ' A German worker, Liihe, was the first to change it -- the very next year -- by adding the 'H ' ; some nomenclaturists thus like to credit him with its authorship. But for nearly 85 years now, most parasitologists have overlooked the faux pas of Caullery and Mesnil (who, themselves, used the cor- rected spelling in all of their subsequent papers), as well as the possible inappropriateness of the (meaning of the) name, and have written it as shown above, despite objections by Sprague (1979).

Assemblage XVIII. The MYXOSPORIDIA A large group of coelozoic or histozoic parasites

mainly of cold-blooded vertebrates (species of a special subgroup occur in invertebrates, mostly annelids) uniquely characterized by having clearly multinuclear plasmodial and multicellular developmental stages in life cycle and one or more polar capsules within valved spores. Mitochondrial cristae fiat, plate-like in appearance. No flagellated forms. Some workers have suggested that these organisms are animals, perhaps degenerate cnidarians. Vernacular name derived from formal name Myxosporidia Biits- chli, 1881, first used at rank or level of order but including essentially same basic subgroups known today. 'Myxosporans' and 'myxozoa ' [latter based on Myxozoa GrassY, 1970 (see Grass~ and Layette, 1978), proposed in support of belief that these organisms are metazoan in nature] are unnecessary names. Single phylum, or possibly two, plus perhaps some small subgroups (for two of which see also Assemblage XVII, above) quite likely best left here, and estimated total number of at least some 1200 generally acceptable species. (see Addendum).

(1) Phylum Myxosporidia Biitschli, 1881 (syns. Myxospora, Myxozoa). Mitochondrial cristae plate- like, fiat. Spores composed of several cells, particularly evident during their development: one or two sporoplasms; one or more (up to 6)capsulogenous cells, becoming polar capsules with internally coiled polar filaments (eventually everted for anchorage in host tissue); and 6--12 valve cells, developing into shell valves. Sexuality known, and zygote may initiate sporulation process; multinucleate plasmodial stage -- reaching diameter of four millimeters and serving as trophozoic stage capable of repeated division -- eventually produces fresh masses of spores. No flagellated stage in life cycle. Shell valves with considerable variation in sculpturing, in appended processes, etc. (all of taxonomic importance). One family of some 300 species noted for distinctive iodinophilous vacuole in sporoplasm. Histozoic or coelozoic endosymbionts of invertebrates (e.g., annelids and oysters) and especially lower vertebrates (notably fishes, where often highly pathogenic to host). Number of described forms now well over 1200

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(J. Lom, pets. comm.), with great majority considered valid and acceptable species.

Note. Are these 'myxozoa ' really metazoan animals, because of stages of multicellularity in their life cycles?Are they related to, or even descended from, cnidarians, with their polar capsules derived from a kind of cnidoblast?Such serious evolutionary questions cannot be resolved without aaditional comparative data, preferably of a biochemical or molecular nature.

(1) Group (=phylum?) Actinomyxidea ~tolc, 1899. In an incertae sedis position primarily with respect to rank: should it be included within or stand independently alongside the preceding phylum? As myxosporidia s.l. (i.e., as members of the assemblage), its species possess many characters that are same as those found in Myxosporidia s.s. (the phylum). But spores here all with three polar capsules (grouped at anterior end) and three spore valves, latter elongated into hooks for attachment to host. One to several sporoplasms, each sometimes multinucleate. Reproduction occurs principally during sporulation sequence, with trophozoic stage (unlike condition in Myxosporidia) reduced in duration and activity. Sexuality present. Nearly all species, some 22 in number, occur in body cavity or intestinal epithelium of aquatic oligochaetes; two species known from body cavity of sipunculids.

(2) Group Marteiliidea Desportes and Ginsburger- Vogel, 1977 (syn. Occlusosporida). Small group of four species (in two genera, Marteilia and Paramar- teilia) in an incertae sedis position primarily for lack of more precise knowledge concerning their characteristics, which appear to be shared with either the Haplosporidia or the Myxosporidia (see above); they also may have some unique features of high systematic value. Parasites of marine mussels and oysters in Europe and Australia (plus one species from amphi- pods in France); vegetative plasmodial stage gives rise to sporangia that, in turn, produce sporoplasms within sporoplasms! Haplosporosomes have been reported from outermost sporoplasm, but not from others. Multicellular origin of spores suggest myxosporidian affinity, but no polar capsules or filaments present.

(3) Group Paramyxidea Chatton, 1911. Single species (from intestinal cells of larvae of pelagic poly- chaete annelid), Paramyxa paradoxa, in an incertae sedis position essentially for same reasons as given above for the Marteiliidea. Nuclear dualism of a sort seems to exist in development of spores, but no polar capsule or filament produced. Single sporoplasm; spore walls not perforated by opening. Levine et al. (1980), in agreement with Sprague (1979, 1982), place this and preceding group within the Haplo- sporidia (called 'Ascetospora' by them), but some French and Czechoslovakian specialists, in particular, are not in full accord with such taxonomic decisions.

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Acknowledgements

The author is deeply indebted to a large number of colleagues and students who, over the years, have contributed ideas and data and/or have acted as a 'sounding board' with respect to both rationale and results exposed here. I am especially appreciative of the help (including unpublished material of their own) and continuing interest of the following quartet of persons: E. Georges Merinfeld, Frederick G. Page, D.J. Patterson, and Lynn Rothschild.

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Addendum

The author is grateful to the editor and printer for being allowed at proof-reading time to include here five references, four of which are cited in the text but were inadvertently omit ted from their alphabetical places above.

The fifth and last paper given below refers to an exceedingly important work that has just appeared in print (September 1984). In brief, Wolf and Markiw (1984) have clearly

shown that a well known myxosporidian species parasitic in certain fish has, as a here-

t o fo re u n k n o w n stage in its full life cycle, a form in a tubificid worm which is congeneric with certain act inomyxidean species! Thus, there m a y be no distinction, no taxonomic separation, at suprafamilial (or even lower) levels between [at least some members of] my 'phylum Myxosporidia' and my 'group (= phylum?) Actinomyxidea. ' This significant discovery serves as a sobering as well as startling example of the crying need for more data before speculating too inflexibly on relationships between or among poorly known groups of protists.

Cavalier-Smith, T., 1983, A 6-kingdom classification and a unified phylogeny, H.E.A. Schenk and W. Schwemmler (eds.), Endocytobiology II: Intracel- lular Space as Oligogenetic Ecosystem, Vol. 2, (Walter de Gruyter, Berlin and New York) pp. 1027--1034.

Corliss, J.O., 1984, The concept and prevalence of xenosomes (cytoplasmic and nuclear endosymbionts) in protists (Abstr.), Proc. 37th Annual Meeting of the Society of Protozoologists, Athens, GA, Aug. 1984, p. 21.

Kumazaki, T., H. Hori and S. Osawa, 1983, Phy- logeny of protozoa deduced from 5S rRNA sequences, J. Mol. Evol. 19,411--419.

Loeblich, A.R., III and L.A. Loeblich, 1983, Dino- flagellate phylogeny and systematics, C.K. Tseng (ed.), Proc. Joint China-U.S. Phycology Symposium, 16--20 November 1981, Qingdao, PRC, (Science Press, Peking) pp. 39--59.

Wolf, K. and M.E. Makiw, 1984, Biology contra- venes taxonomy in the Myxozoa: new discoveries show alternation of invertebrate and vertebrate hosts, Science 225, 1449--1452.

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The kingdom PROTISTA and its 45 phyla