Should there be a separate code of nomenclature for the protists?

BioSystems, 28 (1993) 1 - 1 4 1 Elsevier Scientific Publishers Ireland Ltd.

Should there be a separate code of nomenclature for the protists?

John O. Corliss

P.O. Box 53008, Albuftwrftw, New Me~ivo 87158 (USA)

The present Botanical and Zoological Codes of Nomenclature are often inadequate for resolution of all the peculiar problems caused by the very nature of the numerous and diverse groups of the so-called 'lower' eukaryotic organisms known as protists. Whether or not a separate code should therefore be created for these species -- many but not all of which are unicellular in structure and microscopic in size -- is complicated by several factors. The principal one is related to the wide dispersal of protists throughout many taxonomic classes and phylaYdivisions; sometimes even multiple kingdoms are involved. If recognition of a single kingdom Protista is no longer tenable, then even the concept of one code per kingdom is not applicable. Other dif- ficulties arise primarily from long-standing differences in major provisions of present Botanical and Zoological Codes. Numerous 'ambiregnal' forms exist, species currently under dual code jurisdiction. The matter of names for suprafamilial taxa of protists, irrespective of their ultimate kingdom assignment, poses another set of concerns not yet resolved. A plea is made to recognize the legitimacy of having distinct high-level ranks for protist species that seem to be widely separated phylogenetically from fellow protists or from other eukaryotic assemblages.

Keywords: Codes of Nomenclature; Kingdoms; Protists; Ambiregnal species; Higher taxonomic categories.

1. Introduetion

With the relatively recent acceptance of a more or less distinct high-level taxonomic separation of (most) protists from members of other eukaryotic kingdoms (e.g. Plantae, Animalia, Fungi) and the undesirable situation, which per- sists, of having species of several major protist groups subjected simultaneously to two different International Codes of Nomenclature (the Botanical and the Zoological), a logical question arises, 'Why not wholeheartedly adopt the 'protist perspective' and create a new and separate code exclusively for the allegedly neglected and mistreated assemblage of these so-called 'lower' eukaryotes?'

Recall that codes of nomenclature are more than 'a necessary evil' in biology: they (presumably) guarantee a high degree of stability in infraordinal names, they purport to promote universality of usage and they try to assure the

Correspondence to: John O. Corliss, P.O. Box 53008, Albu- querque, New Mexico 87153, USA.

uniqueness of every taxonomic name, all without significantly interfering with taxonomic freedom (Jeffrey, 1990; Ride and Youn~s, 1986). These are highly laudable aims. Chaos would soon prevail without codes, a potentially threatening condition not always appreciated by workers in fields other than systematics. Cor- rections of errors or oversights, supported or even demanded by the codes, can indeed lead to changes in names. On the other hand, as many alert biologists have been pointing out in recent years, there is a 'ubiquitously acknowledged need to reduce unnecessary name changes' (Hawksworth, 1991a); and the two major codes may, in their present forms, be guilty of allowing, even fostering, name instability mainly because of their emphasis on priority, favoring older, often unknown (until rediscovered) names over ones in wide current usage (Ride, 1991). This vast issue, while relevant enough to mention, is beyond much further consideration in this paper (however see Section 7). Among other things, it involves official recognition of approved lists of names (of plant, animal and other

0303-2647/92/$05.00 © 1992 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

species), a goal that some taxonomists believe might be rather difficult to realize, especially for certain groups of organisms (see references to the literature in Section 7, below).

The question posed above, about introducing a different code for protists (an International Code of Protistological Nomenclature or ICPN), is not an easy one to answer, particularly in the affirmative, because of a number of important factors that need to be taken into consideration. Often, additional questions, also difficult to resolve, arise, as will become clear.

2. One kingdom, one code?

If one were to propose a separate code for protists - for the purposes of argument assumed to comprise a kingdom - should there, then, be a different code of nomenclature for members of every separate kingdom of organisms? It is true that we now have three major codes, one (ICNB, 1975) essentially for the bacteria sensu lato (the prokaryotes), one (ICBN, 1988) for plants (and including algae and fungi) and one (ICZN, 1985) for animals (and including protozoa). The last two groups of organisms comprise the eukaryotes. This is roughly equivalent to one code, one kingdom. But, in recent years, a number of workers have seriously proposed the splitting up of the eukaryotes (alone) into as many as 4 -16 separate kingdoms, of which the Protista may sometimes -- but more often not! - be named as one (Barnes, 1984; Cavalier- Smith, 1981, 1983, 1986, 1989a,b, 1991, 1992a,b; Lipscomb, 1985, 1989, 1991; Margulis et al., 1990; MShn, 1984; Starobogatov, 1984; and see summarizing tables in Corliss, 1986a,c).

Under the notion of one kingdom, one code, we should be obliged to create an individual code for each of the present multiplicity of eukaryotic taxa at that rank. This is clearly not realistic and cannot be used to justify a separate code for either the protists or the fungi, the latter group now widely accepted as a kingdom distinct from the plants even in conservative classifications (Barr, 1992; Corliss, 1984, 1991a; Hawksworth et al., 1983; Kendrick, 1985; Margulis and Schwartz, 1982, 1988; Sleigh, 1989; Whittaker

and Margulis, 1978). Kingdom status alone is not a sufficient reason for arguing that such a group of organisms should be given a separate Code of Nomenclature. Furthermore, even now, codes need not be associated directly with highest-level taxa; for example, all species treated under the Botanical Code are not man- datorially plants (e.g. consider the 'blue-green algae,' in reality cyanobacterial prokaryotes), as botanists readily admit (Jeffrey, 1982; Kirk and Hawksworth, 1986; McNeill and Greuter, 1986).

There are still other reasons, treated in the following sections, which further explain the pros or cons of the proposal for a new code for the protists.

3. Do ambiregnal protists require/deserve a separate code?

Consider the current situation, nomenclatural treatment of some protist species as animals and some as plants (in the terminology of Corliss, 1983b, most algae have been considered to be 'mini-plants,' protozoa 'mini-animals') and some as both (the 'ambiregnal' forms of Patterson, 1986b: see Section 6, below): do these facts serve as a solid basis or reason favoring production of a separate code or special nomenclatural consideration for the entire assemblage of protists? Incidentally, not only are phycological and protozoological taxonomies involved but also mycological. All species of fungi sensu lato are covered by the present Botanical Code, but groups among the traditionally called 'lower' fungi (plasmodial and zoosporic forms now accepted as protists) have also long been treated as protozoa, thus coming under provisions of the Zoological Code.

The situation is serious because, now that systematists have broken down the taxonomic barrier -- at the protist level -- between the old rigid kingdoms of (solely) plants and animals, it is most unfortunate to have what are often phylogenetically closely interrelated taxa treated differently nomenclaturally. Would a new and separate ICPN for protists, however, resolve all aspects of these problems? And how many provisions of such a code would need to

differ significantly from the extensive treatments already included in the present rather hefty Botanical and Zoological Codes? The answer is that rather few sections would need to be revised or be newly added; thus, this way out of the dilemma -- the proposal of a separate, additional code with heavy overlapping in content -- seems ill-advised. Alternative nomenclatural solutions to the continuing problem of the ambiregnal forms, which include fungal as well as algal and protozoan protists, are suggested below (Section 6).

4. Effect of investigator's choice or of legislated action

What if individual taxonomists working with protist species confusingly exploit their current rights to consider the particular organisms under study by them either as algae (or fungi) and therefore subject to the ICBN, or as protozoa and thus coming under ICZN provisions? Or to what extent could or should any international body or committee or commission enforce the scientific community to recognize a given assemblage as treatable under only one system of nomenclatural rules (as suggested by Jeffrey, 1982 and others)? Arbitrary removal of forms or groups (or parts of groups) traditionally govern- ed by the ICBN or the ICZN to new coverage by the other one could wreak havoc on the stability of names already legitimately well established in the literature on those forms. For example, if all dinoflagellates and euglenids were arbitrarily assigned to the ICBN for their nomenclatural justification, then the names of their species previously described under ICZN rules could be put into jeopardy.

5, Do the protists comprise a definable taxonomic entity?

Perhaps the single most serious question of all and the one most devastating to any proposal that a separate code be recognized and accepted for the protists, is this: can a 'protist' be unique- ly defined taxonomically? That is, is there ade- quate justification for recognition of a 'Kingdom

Protista' composed of a singular assemblage of organisms clearly set apart from all other taxonomic assemblages, as I myself (e.g. Corliss, 1981, 1984, 1986b, 1987, 1991a)and many others, have steadfastly maintained?

Our search for unique characters for the entire diverse group of organisms vernacularly called protists has, by hindsight, ended in failure. As has been pointed out -- most recently in some detail by Lipscomb (1991) -- nutritional types are of no help, unicellularity is not univer- sal (e.g. many algal protist groups include species manifesting multiceUular organization), microscopic size has numerous exceptions (consider the brown algae that may reach a length of 60 m!) and such negative characters as lack of multiple tissues (but even this is debatable: again consider the brown algae), lack of organ systems, absence of a complex embryological development in ontogeny and the like are not taxonomically acceptable as unique features of any group.

By turning to a phylogenetic approach to the problem, it has become clear today that the 'Pro- tista' overall do not represent an evolutionarily monophyletic assemblage. Rather, as a kingdom they are comprised of paraphyletic groups at best; in many present definitions of such a kingdom it is indeed a polyphyletic assemblage, in phylogenetic terms (Wiley, 1981). In our recognition of the involvement of multiple kingdoms, we again must inevitably reach the conclusion that a new and single code called 'ICPN' would be an unrealistic and unworkable solution to the nomenclatural problems of all such now scattered protist groups.

Applying phylogenetic principles, using relevant data in greater abundance today than ever before, coming from several different fields or approaches (e.g., electron microscopy and molecular biology), the taxonomic break-up of what was once thought to be perhaps a unified assemblage of protists has become overwhelm- ingly apparent. For example, the green algae must be (re)accepted as plants (or vice versa!) today (Cavalier-Smith, 1981, 1983; Chapman and Buchheim, 1991; and others); the sponges are found to be closely related to protist choano-

flagellates (Cavalier-Smith, 1989a, 1992b; Lead- beater, 1983; Patterson, 1989b); the traditional Mesozoa may be evolutionarily closer to some protists than to (other) animals (Cavalier-Smith, 1989a, 1992b); and certain of the zoosporic groups of fungi may belong (back) in the Fungi fold (Barr, 1992; Cavalier-Smith, 1987). We simply cannot put a circumscription around the protists sensu lato that will allow us to define the realm of a new code.

6. Dilemma of the ambiregnal protists and a proposed solution

How extensive are the ambiregnal groups? Do they represent a very minor problem from a quantitative point of view, as some biologists seem to think (Greuter et al., 1989)? Definitely affected are all dinoflagellates and euglenids; the controversial glaucophytes; many of the flagellates with tripartite hairs, such as the chrysophytes, bicosoecids and pedinellids (Pat- terson, 1989a); the haptophytes (-- prymnesiophytes) and other small groups among the heterotrophic flagellates of the Heterokontae sensu lato (Patterson and Larsen, 1991b); all cryptomonads; and even scattered motile groups among the green algae, including Chlamydomonas and Volvox and related genera of the old chlorophyte class and the prasinophytes. Another group comprise various plasmodial forms, formerly classified with the fungi: the labyrinthulids, the mycetozoaJmyxomycetes sensu lato and the plasmodiophorids. Additional- ly, scattered botanists of the past have treated as algal taxa (thus plants, thereby theoretically subject to regulations of the ICBN) such non- pigmented heterotrophs as those found among the proteromonads, the trypanosomes, the bodonids, the symbiotic parabasalians (trichomonad and hypermastigote flagellates) and even the sponges.

A dozen years ago, I categorized such protists coming under the jurisdiction of both the ICBN and the ICZN as members either of a 'pro- tozoalgal group' or of a 'protozofungal group' (Corliss, 1981). Patterson's (1986b) apt label -- 'ambiregnal' -- highlights the nomenclatural

dilemma facing protistological taxonomists working with such forms and/or with the literature on them. The extensive intermingling of these groups of species with other protists is graphically revealed in the columns of names appearing in Tables I (a-c) and II, irrespective of kingdom designations.

In recent years, several authors have published lists or discussions of suggested ways to solve the dilemma presented by these numerous ambiregnal species of protists (Corliss, 1983, 1986a, 1990, t991b; Jeffrey, 1982; Patterson, 1986b; Patterson and Larsen, 1991a, 1992; Ride, 1982, 1988; Ride and Youn~s, 1986; Silva, 1980b; Taylor et al., 1986, 1987). Nine options, with some overlapping, have been proposed. They may be listed very briefly as follows: amalgamation of all existing codes into a single, unified, new code for all organisms; the 'one code, one kingdom' idea; elimination of 'protists' -- if definable! - from coverage by other codes (then giving them one of their own?); harmoniza- tion (by internal revisions) of provisions of both the ICBN and the ICZN relevant to protist nomenclature; more restrictively, standardiza- tion of the two codes so that only 'phytoflagellates' (however one may define them!) are treated identically under both; arbitrary alloca- tion of some protist taxa to treatment under one code, others under the other; designation of an international committee/commission to serve as arbitrator in nomenclatural disputes brought to its attention by taxonomic protistologists; re- quirement that persons working with ambiregnal forms follow all the rules of both major codes; allowance of freedom of choice (as to which code to apply to his/her problem) to any author of a taxonomic/nomenclatural work on such protists.

There is quite general agreement that the ideal solution, production of a single code for all organisms (even prokaryotes), is simply too unrealistic and therefore not feasible. While such an ecumenical approach may be a great ultimate goal, the havoc and chaos that would inevitably be caused along the way (i.e. the effect on hundreds of names already well established in the literature following provisions of the

Table I. (a) Major assemblages of plants, animals and fungi in a representative 1972 two-kingdom arrangement. Under 'Fungi,' the asterisk (*) indicates groups at least some species of which are simultaneously claimed by botanists and zoologists. (b) Major high-level assemblages of algae (within the plant kingdom) in a representative 1972 classification. The asterisk (*) indicates groups at least some species of which are simultaneously claimed by beth botanists and zoologists. These 'ambiregnal' forms, although here with a formal kingdom association of solely PLANTAE, could be treated under the ICZN as well as under the ICBN (see text and also Table I(c)). (c) Major high-level assemblages of protozoa (within the animal kingdom) in a representative 1972 classification. The asterisk (*) indicates groups at least some species of which are simultaneously claimed by both zoologists and botanists. These 'ambiregnal' forms, although here with a formal kingdom association of solely ANIMALIA, could be treated under the ICBN as well as under the ICZN (see text and also Table I (b)).

Colloquial or Formal Kingdom Applicable code of informal names association nomenclature and comments

(a) Animals sensu late ANIMALIA

Plants s.l. PLANTAE

Fungi s.1. Basidiomycetes Ascomycetes Zygomycetes Chytrids Oomycetes Hyphochytrids

*Labyrinthulids s.l. *Myxomycetes s.l. *Plasmodiophorids s.1.

PLANTAE

ICZN. Multiple phyla, beyond consideration here, recognized, with 'Protozoa' (see Table I(c)) an included group in the kingdom. ICBN. Several divisions, beyond consideration here, recognized, with 'Algae' (Table I(b)), 'Fungi' (see below) and cyanobacteria included in the kingdom. ICBN + a few (groups with asterisk) potentially under ICZN. First 3 groups (Eumycota} beyond further consideration here. Others contain zoosporic or plasmodial forms, last 3 of which also recognized by zoologists (thus with 'ambiregnal' species: see text and Table lc)

Colloquial or informal (vernacular) names in common use (year 1972)

Algae s.1. Blue-greens (cyanophytes) Greens (chlorophytes s.1.)

*Chlorophytes s.s. *Prasinophytes Charophytes Ulvophytes

Golden-browns (chromophytes, heterokonts) *Chrysophytes s.s. * Synurophytes *Bicosoecids Diatoms (bacillariophytes) * Silicoflagellates * Pedinellaleans *Haptophytes (prymnesiophytes) *Rhaphidophytes

(c) Protozoa s.1.

Rhizopod 'sarcodinids' s.1. Naked and testate amoebae s.1. Pelobiontids

Yellow-greens *Xanthophytes *Eustigmatophytes

Browns (phaeophytes) Reds (rhodophytes) *Glaucophytes *Cryptophytes *Eugienophytes *Dinoflagellates (pyrrhophytes) *Craspedophytes (collar-flagellates)

'Zooflagellates' s.l. *Proteromonads s.l. *Bicosoecids

Foraminifers *Mycetozoa s.l. *Labyrinthulids s.l. * Plasmodiophorids Xenophyophorids

Actinopod 'sarcodinids' s.l. Heliosoa s.l . Acantharians Radiolarians s.l.

'Phytoflagellates' s.l. *Phytomonads *Chrysomonads *Silicoflagellates *Haptomonads *Cryptomonads * Euglenids *Dinoflagellates *Ebriideans

*Bodonids *Trypanosomatids Polymastigotes s.l. Trichomonads Hypermastigotes Opalinids

*Choanoflagellates Sporozoa (apicomplexans)

Gregarines, coccidians haemo-, and hapio-sporidians

'Cnidosporidians' Micro-, myxo-, helico-sporidians, ac~inomyxidians

Ciliates Holo-, spiro-, peri-, chono-trichs, suctorians

Table II. Major high-level assemblages of (mainly) protists (within multiple eukaryotic kingdoms, basically the six promoted by Cavalier-Smith, 1989a,b, 1991, 1992a,b: see text) in a very recent (1992), and tentative, classification scheme (cf. Tables la-c). The asterisk (*) indicates groups at least some species of which are 'ambiregnal,' coming under the jurisdiction of the two codes, ICBN and ICZN, as shown in the third column.

Colloquial, informal, or vernacular names

Formal Kingdom associations (b la Cavalier-Smith)

Applicable codes of nomenclature and comments

Protists s.l.

Blue-green algae (cyanophytes)

Pelobiontlds 'Polynmstigotes' (metamonads)

Microsporidians Rhisopod amoebae

(many subgroups) Foraminlf" ers *(Eu)mycetozoa

(myxomycetes) *Plasmodiophoreans *Ebrh'deans Xenophyophorans * Euglenozoa/-phytes *Kinetoplastldans (bodonids, tryps)

*Proteromonads + opalinids

*Choanoflagellates (craspedophytes)

Chytrids Green algae (includes the protozoan *phytomonads)

Several: see entries below the blue-greens EUBACTERIA (prokaryotic) #ARCHEZOA #ARCHEZOA

#ARCHEZOA @PROTOZOA

@PROTOZOA @PROTOZOA

@PROTOZOA @PROTOZOA @PROTOZOA(?) @PROTOZOA @PROTOZOA

@PROTOZOA (or CHROMISTA s.l.?) @PROTOZOA

FUNGI PLANTAE (subkingdom VIRIDIPLANTAE)

Currently still ICBN and/or ICZN: see text, Tables la-c , and asterisk'd names.

ICBN (but cyanobacteria: shown for completeness)

ICZN ICZN (polyphyletic group, obscure relationships?)

ICZN ICZN ('rhizopods' still polyphyletic, overall?)

ICZN ICBN/ICZN

ICBN/ICZN ICBN/ICZN ICZN ICBN/ICZN ICBN/ICZN

ICZN (mostly)

ICBN/ICZN (possibly in kingdom ANIMALIA?)

ICBN ICBN (mostly; see sub-groups in Table lb)

Reds (rhodophytes) + *giaucophytes

*Golden-brewus s.l. (syus. ~: chrysophytes s.l., chromophytes, heterokonts, stramenopiles -~ )

*Yellow-greeus (xanthophytes, eust~gmatophytes)

Browns (phaeophytes) CHROMISTA *Cryptophytes/- m o n a d s CHROMISTA

(sk. CRYPTISTA) p ~ l i a n s @PROTOZOA

(trichomonads, hyper- mast~otes)

*Heliosoa s.l. CHROMISTA and/ (several subgroups) or @PROTOZOA?

Acantharians @PROTOZOA Radiolarians s.1. @PROTOZOA

(polycystines, phaeodarians)

Myxosporidiaus @PROTOZOA Haplosporidians @PROTOZOA Apicomplexaus @PROTOZOA

(sporo-oa +) (sk. ALVEOLATA) *Dinoflagellates @PROTOZOA (pyrrhophytes) (sk. ALVEOLATA)

Ciliates @PROTOZOA (8 major classes) (sk. ALVEOLATA)

PLANTAE (sk. BILIPHYTA) CHROMISTA s.l. (sk. CHROMOBIOTA)

CHROMISTA

ICBN (mostly; glaucephytes better separate?)

ICBN (but some also under ICZN: see asterisk'd groups in Tables lb,c; composition of entire assemblage controversial!)

ICBN/ICZN (polyphyletic group?)

ICBN ICBN/ICZN (deserve separate kingdom of own?)

ICZN

ICZN, some ICBN (polyphyletic group?)

ICZN ICZN (polyphyletic group?)

ICZN (possibly in kingdom ANIMALIA?) ICZN ICZN

ICBNHCZN

ICZN

#ARCHEZOA may well be a polyphyletic kingdom; and the choice of name is undesirable because of earlier usages (most notably by Ernst Haeckel, a century ago, for the bacteria) ~or assemblages of quite different organisms. @PROTOZOA, apart from probably being a polyphyletic assemblage here, has long (for some 175 years!) and conventionally been the name used to embrace all the 'typical' protozoan protists of the literature. In recent times, the writer and others have suggested its complete abandonment -- as a formal taxonomic name spelled with a capital 'P' -- in that older context and this proposal has met with wide acceptance. Thus, its resurrection at this time by Cavalier-Smith for a quite different, restricted usage is most regrettable.

existing codes) would be, in the opinion of many of us, far too extensive for biologists to bear.

The best and most practical solution, f rom my point of view, is a compound one involving the several actions or steps tha t I am proposing below. They will need to be under taken agreeably and in parallel by the bodies or com- missions present ly responsible for amending and emending the 'big two' (ICBN, ICZN) Codes of Nomenclature.

First, cur ren t significant differences in these

codes and how these affect names of ambiregnal species, must be clearly outlined and under- stood. This alone is not an impossible task; indeed, Jeffrey (1986), Patterson and Larsen (1992) and Taylor et al. (1986, 1987) have iden- tiffed and discussed many of the principal differences. They number more than two dozen, however, and are too lengthy and/or too technical to be treated or even listed in the present paper. Secondly, new editions of the codes involved

must either accommodate most of the differences (i.e. agree on ways to harmonize each former conflict) and treat all names essentially the same or include provisions protecting the conservation of certain names (by a 'grand- father' clause) up to a specified date beyond which more liberalizing, uniform rules would come into force.

Thirdly, recognizing the general stability en- sured by introducing as little change as possible, the revised codes ought to have special provisions allowing exceptions of various kinds in cases of ambiregnal protist species. In some in- stances, the governing bodies will have to pro- ceed practically on a case-by-case basis. Both codes already have conservation mechanisms for protection against too stringent use of the Principle of Priority. Relaxation of certain rules would minimize nomenclatural changes in cases of established species belonging to the many am- biregual taxa listed above. (This recommenda- tion may be considered to overlap somewhat with the preceding one.)

Finally, new provisions in both codes ought to contain, or at least make reference to, a set of guidelines that formally or informally suggest ways to resolve past -- and avoid future - con- flicts with respect to names and ranks of suprafamilial taxa (see further discussion in Sec- tion 7, below). Patterson and Larsen (1991a, 1992) have commented on this matter as well; and they have stressed that the strict adoption of phylogenetic criteria might help significantly in stabilizing the situation at such high levels. The likely resulting nomenclatural innovations could be made more palatable, perhaps, by including explanations of their general relationship to groups named differently in the vast past literature, 'bridging the gap' somewhat as I have attempted to do, succinctly, in Tables I (a-c) and II.

Such positive actions as those outlined above will take time; voluntary co-operation will be an essential ingredient for successful resolution of all the problems involved. But here, once again, creation of a separate code for protists (including the ambiregnal forms) is an alternative solution that I reject for reasons generally already presented elsewhere above.

7. Nomenclature above the family level

A separate-but-related matter deserving further mention is that of suprafamilial, with emphasis on supraordinal, nomenclature, not only for protist taxa but for all eukaryotic taxa. Non- taxonomists sometimes believe -- incorrectly and/or inadvisedly -- that the codes control, or should have jurisdiction over, the names of (groups of) organisms above the level of family. With very minor exceptions (mostly in the ICBN), they do not and, most of us believe, should not (although see arguments in papers by Brothers, 1983; Rasnitsyn, 1982; and Starobogatov, 1991).

Nevertheless, there is an unfortunate aspect of having no internationally approved set of guidelines concerning names and naming of high-level taxa in that individual authors can at will propose names for newly created groups or even for just an elevation in the rank of taxa that were formerly lower in the hierarchical system. This has led to a rash of rather irrespon- sible name-giving (Corliss, 1972, 1983a, 1990), an undesirable and 'undisciplined proliferation' of names (Patterson and Larsen, 1991a), accompanied by inflation of taxonomic ranks, that was particularly prevalent in the 1970s and early 1980s. Today, many such names are or soon will be falling either into total disuse or into semi- oblivion as synonyms of other perfectly good names for essentially the same groups of organisms, taxa now being established on the sound basis of phylogenetic criteria (Lipscomb, 1989, 1991; Patterson, 1989a,b; Patterson and Larsen, 1992). To avoid some of these pitfalls in the future serves as a basis for my proposing (in Section 6, above) the drawing up of specific guidelines for suprafamilial nomenclature, recommendations to be included - in some way - in new editions of the codes.

The problem of unnecessary name-changing, as already noted briefly above (in the Introduc- tion) with respect to the lower taxonomic ranks, rears its ugly head again here. The non- taxonomic community's disgust (e.g., Barnett, 1988; Crisp and Fogg, 1988; Hawksworth, 1991; Hawksworth and Bisby, 1988) with the seem- ing/perceived instability of taxonomic nomen-

clature has hardly been appeased by the multiple names that have been bestowed upon suprafamilial groups of protists during the past 20 years. Solution of this particular instability problem is, as indirectly mentioned above, em- bodied in recent proposals -- by both zoologists (e.g. Ride, 1991) and botanists (e.g. Bisby and Hawksworth, 1991; Greuter, 1986; Hawksworth and Greuter, 1989) -- that involve preparation of Lists of Approved Names, specification of approved journal(s) for publication of new taxa/names, etc., more or less following the revolutionary lead of the bacteriological community (Skerman et al., 1980; Sneath, 1986).

Despite some overzealousness in frenzied production of new names and groups in recent times, there is clearly a justifiable need -- because of the explosion in protist taxonomic discoveries and the dramatic changes in our understanding of protist relationships -- for ex- pansion both in numbers of taxa and in levels of ranks (and in the names properly associated with such actions). In fact, this was perceptively foreseen half a century ago by Copeland (1956). Now, results of comparative studies by electron microscopy alone during the past 20-30 years require the recognition of many new groups. In order to maintain the desirable phylogenetic perspective, numerous old and new groups must be acknowledged as needing separation at sometimes very high taxonomic levels in the hierarchical system. For the sake of clarity and to avoid ambiguity, changes in circumscription and/or in composition of any high-ranked taxa should, according to Patterson and Larsen (1991a), be accompanied by creation of a new appropriate name. (Are courtesy and common sense (Corliss, 1972) soon to become entirely out of vogue?!?)

The choice and/or formation of names for suprafamilial taxa, especially (indeed, usually) involving protists (the eukaryotes undergoing the greatest taxonomic explosion these days), is a topic too detailed to consider here. Never- theless, brief mention is made of it because the reader should appreciate the subject's general relationship to the overall problem of the nomenclature and rank of high-level groups (for further information, consult the following re-

cent papers and their bibliographies: Barr, 1992; Cavalier-Smith, 1991, 1992c; Christensen, 1989, 1990; Corliss, 1991b; Hawksworth, 1991b; Heywood and Rothschild, 1987; Margulis and Sagan, 1985; Patterson, 1989a,b; Patterson and Larsen, 1991a, 1992; Rothschild and Heywood, 1988; Round, 1984; Sieburth and Estep, 1985; Silva, 1980a, b, 1984; Starobogatov, 1991).

8. Genera versus higher ranks and incertae sedis species

Another topic relevant to the general theme of this overview paper concerns the recent emphasis by some of our colleagues, in works on the taxonomy or phylogeny of protists, on the generic level of their newly described organisms (e.g. see Larsen and Patterson, 1990; Patterson, 1989b; Patterson and ZSlffel, 1991). This approach is admirable in many respects, but the fact remains that the scientific community at large plus non-scientific users of names and information retrieval systems people, not to mention teachers of biology and their students and the lay public in general, are demanding and will continue to ask for and expect to get a reasonably neat set of named high-level taxa for all organisms, even if these users are (or need to be) frequently cautioned that such an overall classification scheme, perforce, may be of a rather tentative or tenuous nature. Perhaps it is a weakness of human nature to desire such orderliness. The paradox is that while older perspectives are often being found, today, to be incorrect and/or misleading, the newer, phylogenetically based understandings of group relationships are quite frustratingly incomplete for many of the '70 - 110 types' (D.J. Patterson, pers. commun.) representing the currently perceived diversity among the eukaryotes of the Earth. What to do in the interim?

Taken in historical perspective and reflecting only the point of view of biologists working with protists, there has always been a desire to and an obvious advantage in, grouping species and genera into manageable higher categories (Cor- liss, 1984). In the early days, the family was often the most common higher category for both the

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algae and the protozoa. Families were sometimes quite huge and improved methods of study even- tuany revealed both the wisdom and the necessi- ty of splitting them up into subfamilies and/or independent families. In due time, the latter became grouped into separate suborders or orders, themselves often eventually gathered into a smaller number of superorders or subclasses or even classes. For many decades, now, the class has been a favorite high-level rank for phycologists; until quite recently, the order has been the most popular choice of protozoologists - that is, the name most often used in the vernacular or as the designated group-name for the particular organisms under study by a given in- vesrigator. But, following recent hierarchical in- flations, the protozoologist has also been apt to adopt class or subclass names for more general usage. Today, protistologists are more and more frequently embracing divisions or phyla to their respective bosoms (to better indicate evolutionary separateness), especially as such taxa are being subsumed as parts of discrete kingdoms. See, for example, my Table II, in which I have used Cavalier-Smith's (1989a,b, 1991, 1992a,b) six eukaryoric kingdoms, without necessarily fully en- dorsing them, as tentative homes for the diverse high-level protistan assemblages.

Controversial is the decision, today, of what to do taxonomically with the discovery/description of species seemingly without any close relatives. One school of thought prefers elevating these unique forms to the position of sole represen- tatives of a new class or even phylum or division. The writer joins such colleagues as Cavalier- Smith, Foissner and Hibberd in generally holding this viewpoint {e.g. Cavalier-Smith, 1983, 1986; Corliss, 1984; Foissner et al., 1988; Hibberd, 1984; Hibberd and Norris, 1984; Lipscomb and Corliss, 1982). We do insist that the organism's combination ('constellation') of distinguishing characteristics (usually ultrastructural in nature) prevents its ready assignment to other existing protist groups, all the way up the taxonomic scale. In phylogeneric terms, it must be (or appear to be, based on the evidence available) a monophyleric entity, even if represented by a single species. There is

nothing in evolutionary theory that requires the survival - or discovery -- of multiple species or genera in order to recognize the phylogenetic or taxonomic high-level distinctiveness of a single species among many other groups of organisms assignable to the same kingdom.

Another school favors labeling such seemingly unique species as 'incertae sedis protists,' keep- ing their rank (their higher taxonomic vehicle) as low as family or even genus (as mentioned above). This view is strongly held by Patterson and such colleagues as Larsen, VCrs and others (e.g., Brugeroile and Patterson, 1990; Larsen and Patterson, 1990; Patterson, 1986a, 1990; Patterson and Brugerolle, 1988; VCrs, 1988). Their view is a cautious one, based on the often patchy nature of relevant available data. Presumably, when pertinent phylogeneric infor- marion becomes available, appropriate taxonomic shifts can be made. I can appreciate the fact that difficulty may exist in determining which, if any, of the existing suprafamilial taxa might best serve as a home for the isolated new organism. I can also see, however, distinct disadvantages in merely attaching it to some all- inclusive taxon having the very high rank of kingdom, grade, clade, or domain. Even if it is unprovable at that moment, the organism must be more closely related to some group (e.g. to the stramenopiles as opposed to the totally different apicomplexans; or to the euglenids as con- trasted with the microsporidians; or to the ciliates rather than the acantharians; etc.) among the major protist assemblages. If so, why not attach it as incertae sedis to one such major group bearing an infrakingdom rank? If other- wise, its uniqueness as a representative of an entirely new high-level taxon should be fully acknowledged, even if tentatively.

9. Effect of growth of protistology on its nomenclatural problems

As is well known (Corliss, 1986a), there has been a phenomenal development of the field of protistology during the past few decades as techniques of study have improved and as in- terest in the implicated organisms has grown. Cell, evolutionary and molecular biologists -- as

well as taxonomists and ecologists -- have perceived the value of many protistan species in their own areas of specialization. Inevitably, hundreds of new species have been discovered and scores of new suprafamilial taxa have been erected. Taxonomically, the situation has become nearly chaotic; and, accompanying the burgeoning growth in the macrosystematics .of these newly described eukaryotic groups, problems of a nomenclatural nature have surfaced in great numbers.

While the 'protist perspective' has been a healthy one, it has now become apparent that a single taxonomic kingdom Protista is unsuppor- table on phylogenetic grounds. Production of a Code of Nomenclature for protists sensu lato is an unworkable and unnecessary, solution to the multiplicity of nomenclatural problems involved, as argued on preceding pages.

A proposal related to solving the predicament of the so-called ambiregnal protists (groups indicated with an asterisk in Tables I (a-c), II) at the level of the existing Codes of Nomenclature has been outlined above (Section 6). Such forms represent a considerable percentage of all the known protist species. Matters related to the names and naming of high-level taxa beyond current jurisdiction of the codes are even more complicated and require fuller attention than has been possible to give them here. But my two tables are offered as a way both of summarizing the brief discussions offered in the text concerning suprafamilial ranks and taxa and of in- dicating the magnitude of the problem at those levels.

In an at tempt to 'bridge the gap' between past, conventional systems of macroclassifica- tions of eukaryotes (with emphasis on what have become protist groups), Table I (a-c) offer historical background data on such organisms, as of some 20 years ago, with deliberate use of vernacular names below the kingdom level. The applicable Codes of Nomenclature are also indicated. Table II, a much more difficult one to prepare because it involves very recent group- names sometimes conceptually meaning different things to different workers, is nevertheless considered necessary to illustrate -- if nothing else -- the growth in complexity of the

11

situation in modern times. In order to indicate possible 'formal kingdom associations,' I had -- at the time of writing - only two options: use some classification in the recently published literature, or devise a totally new and original one of my own. I opted for using an available one in order not to confound the picture still more! In utilizing the six-kingdom notion of colleague Cavalier-Smith (1989a, b, 1991, 1992a,b), I am not implying my own full endorsement of the particular names he uses (I am especially distressed by the novel usage of the venerable term 'Protozoa'; in the present instance, however, I can see no way to avoid this specific dilemma). Unfortunately, perhaps, to date no critic of the Cavalier-Smith scheme has offered a different full and formal classification embracing all eukaryotes. When a group in the lefthand column of the table is probably -- or perhaps - not a monophyletic one, this is so indicated under my 'comments' in the righthand column.

It is important to note that, in both tables, the vernacular names are used without any reference to the level or rank of the groups they represent. This has been done intentionally, for it is premature, in my opinion, to propose specific taxonomic ranks for these groupings. At least, such action should not be taken without a full explanation or critical discussion in the text proper, an assignment well beyond the limits of the present paper. What I have done in the tables, in addition to 'bridging the gap' between representative classifications 20 years apart (arbitrarily, 1972 and 1992), is to reveal the tremendous taxonomic intermingling, today, of (former) algal, fungal and protozoan groups; to indicate their present code affiliations; and to demonstrate the high-level phylogenetic/evolutionary separation of various assemblages by their (tentative) assignments to multiple kingdoms (whatever names the latter may ultimately bear).

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Should there be a separate code of nomenclature for the protists?