35
This chapter is dedicated to my mother, Helen Jean Siver. Thanks, Mom I. INTRODUCTION The Synurophyceae is a relatively new class of algae based primarily on differences in biochemical and ultrastructural characteristics (Cavalier-Smith, 1986; Andersen, 1987). The organisms contained in the Synurophyceae were previously placed in the family Mallomonadaceae Diesing (sensu Hibberd, 1976; Bourrelly, 1981), also referred to as the Synuraceae (e.g., Wee, 1982; Starmach, 1985), in the class Chryso- phyceae. Wee (1982) listed 10 genera within the family Synuraceae (or Mallomonadaceae): Synura, Micro- glena, Mallomonas, Chrysosphaerella, Conradiella, Paraphysomonas, Mallomonopsis, Chlorodesmus (also known as Catenochrysis and Phillipsiella), Chryso- didymus, and Spiniferomonas. All genera within the Mallomonadaceae possessed a cell covering composed of siliceous scales and commonly were referred to as scaled chrysophytes. In a review of the class Chrysophyceae, Hibberd (1976) recognized that the ultrastructure of some genera in the Mallomonadaceae deviated substantially from that of Ochromonas, the genus considered as the type for the class. Preisig and Hibberd (1983, 1986) removed Paraphysomonas, Spiniferomonas, and related genera from the Mallomonadaceae based on differ- ences in cell structure and placed them into a new family, the Paraphysomonadaceae. Preisig and Hibberd 523 14 SYNUROPHYTE ALGAE Peter A. Siver Botany Department Connecticut College New London, Connecticut, 06320 I. Introduction II. Diversity and Morphology A. General Characteristics B. Scale and Bristle Anatomy C. Arrangement of Scales on the Cell Surface D. Cysts Life Cycle, and Cell Division E. Taxonomic and Phylogenetic Considerations III. Ecology and Distribution A. General Comments B. Primary Habitat Requirements C. Distribution along a pH Gradient D. Distribution along a Dissolved Salt Gradient E. Distribution along a Trophic Gradient F. Distribution along a Temperature Gradient IV. Collection and Preparation for Identification A. Collection of Samples B. Preparing Samples for Observation with Light Microscopy C. Preparing Samples for Observation with Electron Microscopy D. Storage of Samples and Preparations of Scales and Bristles V. Keys to Genera and Common Species from North America A. Introduction to Keys B. Key to Genera C. Descriptions of Genera D. Key to Common Species of Mallomonas E. Key to Common Species of Synura VI. Guide to Literature for Species Identification Literature Cited Freshwater Algae of North America Copyright © 2003, Elsevier Science (USA). All rights of reproduction in any form reserved.

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Page 1: Freshwater Algae of North America || SYNUROPHYTE ALGAE

This chapter is dedicated to my mother, Helen JeanSiver. Thanks, Mom

I. INTRODUCTION

The Synurophyceae is a relatively new class ofalgae based primarily on differences in biochemical and ultrastructural characteristics (Cavalier-Smith,1986; Andersen, 1987). The organisms contained inthe Synurophyceae were previously placed in the familyMallomonadaceae Diesing (sensu Hibberd, 1976;Bourrelly, 1981), also referred to as the Synuraceae(e.g., Wee, 1982; Starmach, 1985), in the class Chryso-phyceae. Wee (1982) listed 10 genera within the familySynuraceae (or Mallomonadaceae): Synura, Micro-

glena, Mallomonas, Chrysosphaerella, Conradiella,Paraphysomonas, Mallomonopsis, Chlorodesmus (alsoknown as Catenochrysis and Phillipsiella), Chryso-didymus, and Spiniferomonas. All genera within theMallomonadaceae possessed a cell covering composedof siliceous scales and commonly were referred to asscaled chrysophytes.

In a review of the class Chrysophyceae, Hibberd(1976) recognized that the ultrastructure of some genera in the Mallomonadaceae deviated substantiallyfrom that of Ochromonas, the genus considered as thetype for the class. Preisig and Hibberd (1983, 1986)removed Paraphysomonas, Spiniferomonas, and relatedgenera from the Mallomonadaceae based on differ-ences in cell structure and placed them into a new family, the Paraphysomonadaceae. Preisig and Hibberd

523

14SYNUROPHYTE ALGAE

Peter A. SiverBotany DepartmentConnecticut CollegeNew London, Connecticut, 06320

I. IntroductionII. Diversity and Morphology

A. General CharacteristicsB. Scale and Bristle AnatomyC. Arrangement of Scales on the

Cell SurfaceD. Cysts Life Cycle, and Cell DivisionE. Taxonomic and Phylogenetic

ConsiderationsIII. Ecology and Distribution

A. General CommentsB. Primary Habitat RequirementsC. Distribution along a pH GradientD. Distribution along a Dissolved

Salt GradientE. Distribution along a Trophic GradientF. Distribution along a Temperature

GradientIV. Collection and Preparation for

Identification

A. Collection of SamplesB. Preparing Samples for Observation

with Light MicroscopyC. Preparing Samples for Observation

with Electron MicroscopyD. Storage of Samples and Preparations

of Scales and BristlesV. Keys to Genera and Common Species from

North AmericaA. Introduction to KeysB. Key to GeneraC. Descriptions of GeneraD. Key to Common Species

of MallomonasE. Key to Common Species of Synura

VI. Guide to Literature for SpeciesIdentification

Literature Cited

Freshwater Algae of North AmericaCopyright © 2003, Elsevier Science (USA). All rights of reproduction in any form reserved.

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clearly demonstrated that organisms in the Paraphyso-monadaceae had a cell structure that was similar tothat of Ochromonas and Chromulina, but quite differ-ent from other members of the Mallomonadaceae,namely Mallomonas and Synura. Shortly thereafter,Andersen (1987) moved Mallomonas and Synura outof the class Chrysophyceae and placed them into a newclass, the Synurophyceae.

There are currently four genera recognized withinthe Synurophyceae. Three of the genera, Mallomonas,Synura, and Chrysodidymus, are reported commonlyfrom North America, and contain about 160 recog-nized species or subspecific taxa (Moestrup, 1995).Tessellaria, a fourth genus more recently assigned tothe Synurophyceae, is known from Australian waters(Tyler et al., 1989; Pipes et al., 1991), but has not beenreported from North America. A fifth genus, Mallo-monopsis, was originally separated from Mallomonason the basis of possessing two, rather than one, emer-gent flagella (Matvienko, 1941; Wujek and Timpano,1984). Belcher’s (1969) recommendation to combinethese two genera was supported by Andersen’s (1987)conclusion that the occurrence of two basal bodies andtwo flagella appeared to be universal among membersof the genus Mallomonas. Such a proposal was fol-lowed in many subsequent taxonomic works, includingMomeu and Péterfi (1979), Asmund and Kristiansen(1986), and Siver (1991a), and has been supported byphylogenetic analyses using scale covering charactersand molecular data (Lavau et al., 1997). Chlorodesmushispidus was shown by Calado and Rino (1994) to be a morphological form of, and synonymous with,Synura spinosa. As noted by Wee (1982), Kristiansen(1988a), and Leadbeater and Barker (1995), the taxonomic positions of the rarely observed generaConradiella and Microglena remain unclear. Kristiansen(1988a) has suggested that Conradiella, originallydescribed by Pascher (1925) as a unicellular organismsurrounded by transverse rings of silica, may actuallyrepresent a misidentified Mallomonas.

II. DIVERSITY AND MORPHOLOGY

A. General Characteristics

All synurophytes are motile flagellates that consistof either a unicellular or colonial habit (Figs. 1–3).Cells contain one bilobed or two golden-coloredchloroplasts that generally are positioned such thattheir long axes are parallel to each other and to thelong axis of the cell (Fig. 1). All species possesssiliceous scales that either surround individual cells(Chrysodidymus, Mallomonas, and most species ofSynura) or are situated in multiple layers around the

colony (Synura lapponica and Tessellaria; Skuja, 1956;Wujek and Wee, 1983; Tyler et al., 1989; Siver andGlew, 1990; Figs. 1–3). Each cell has two parallelaligned and apically inserted flagella that emerge eitherfrom a pore in the anterior end of the scale coat(Fig. 3E) or through the scale matrix on the surface ofthe colony (Fig. 3F). For all species of Mallomonas,except for taxa within the sections Mallomonopsis,Multisetigerae, and Papillosae, only a single emergentflagellum can be seen with light microscopy (LM;Asmund and Kristiansen, 1986; Siver, 1991a). The partof the cell with the flagella is referred to as the anteriorend and the nonflagellated end is denoted the posteriorend.

Although some species of Mallomonas are sphericalunicells, most possess ovoid or ellipse-shaped cells(Figs. 1A and B, and 3A–D; Siver, 1991a). In additionto siliceous scales, species of Mallomonas also haveelongated siliceous structures called bristles that areassociated with all or selected scales on the cell cover-ing (Figs. 1A–E, and 3A and D). Only one species ofMallomonas, M. adamas, is thought to lack bristles(Lavau et al., 1997). The bristles are tucked under thedistal ends of the scales in such a way that when thecells are actively swimming the bristles become stream-lined and parallel with the long axis of the cell.Common morphologies for Mallomonas taxa includecells where the bristles are (a) restricted to the anterior-most scales that immediately surround the flagellarpore (e.g., M. dickii; Fig. 13C), (b) restricted to scaleson the anterior end of the cell (e.g., M. tonsurata;Fig. 1E), (c) distributed over most of the cell (e.g., M. transsylvanica; Fig. 3A), and (d) where distinctlydifferent types of bristles are found on different partsof the scale coat (e.g., M. hamata). In addition, manyspecies of Mallomonas have scales with spines that arepositioned on the posterior end of the cell (Fig. 3B).Spines can range from being quite small, less than 1 μm(e.g., M. dickii) to over 10 μm in length (e.g., M.torquata; Siver, 1991a). Most species of Mallomonashave cells that range in size from 10 to 50 μm long and5 to 20 μm wide, although larger and smaller cells canbe observed (Siver, 1991a). Size records and morpho-logical details for many species can be found inTakahashi (1978), Wee (1982), Asmund and Kristiansen(1986), and Siver (1991a, b). Mallomonas is a cosmo-politan genus (see Asmund and Kristiansen, 1986) thatis observed in collections throughout North America(Nicholls, 1988a; Siver, 1991a).

Species of Chrysodidymus, Synura, and Tessellariaare colonial flagellates where each cell of the colonyhas two clearly visible emergent flagella. Colonies ofChrysodidymus consist of two somewhat elongatedcells that are attached at their posterior ends and face

524 Peter A. Siver

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14. Synurophyte Algae 525

FIGURE 1 Light micrographs of Mallomonas cells and Synura colonies. A. Four cells of Mallomonascaudata. Scale bar = 20 μm. B. Close-up of a cell of Mallomonas caudata focused on the outer surface.Note the overlapping oval scales and the proximal ends of the bristles. Scale bar = 20 μm. C. Cell of Mallomonas caudata beginning to encyst. Note the large central vacuole, chloroplast, and the over-lapping nature of the scales. Scale bar = 20 μm. D. Cell of Mallomonas corymbosa where the intactprotoplast has squeezed out from the scale coat. The two chloroplasts and a small portion of the flagellum can be observed, as well as scales and bristles. Scale bar = 10 μm. E. Remains of the scalecoat of Mallomonas tonsurata. Note the overlapping scales, the restriction of the bristles to the anteriorend of the cell, and the forked tips of the bristles. Scale bar = 10 μm. F. Colony of Synura peterseniiwith only a few club-shaped cells with long caudal tails. Scale bar = 20 μm. G. Elongated colony ofSynura spinosa. Note the apical scales with long spines. Scale bar = 20 μm. H. Chorodesmus-like formof Synura spinosa. Scale bar = 20 μm. I. Squashed colony of Synura petersenii denoting club-shapedcells. Scale bar = 20 μm.

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outward at 180° from each other (Fig. 2A and B). Thecells of recently formed colonies of Chrysodidymustend to be globose or spherical in shape. As coloniesage, the cells become more elongated and vaselike, andthe posterior portion is distinctly wider than the flagel-lated end (Graham et al., 1993). Whereas colonies ofTessellaria and Synura, including those with two cells,tend to have a rolling or tumbling swimming motion,colonies of Chrysodidymus oscillate back and forthalong their longitudinal axes (Nicholls and Gerrath,1985; Graham et al., 1993). Although rarely observedin most collections, Chrysodidymus has been found ina number of localities in North America, includingQuebec (Puytorac et al., 1972), Ontario (Nicholls andGerrath, 1985), the midwestern United States (Wujekand Wee, 1983; Wujek and Igoe, 1989; Graham et al.,1993), Florida (Wujek and Bland, 1991), theAdirondacks of New York (Siver, 1988a; Cumming et al., 1992a), Washington (Norris and Munch, 1970),southern New England (Siver and Hamer, 1992), andLouisiana (Wee et al., 1993). Chrysodidymus also hasbeen observed in South America (Dürrschmidt, 1982;Wujek and Bicudo, 1993), Greenland (Nygaard, 1978),Germany (Hartmann and Steinberg, 1989), and tropi-cal localities (Prowse, 1962; Hansen, 1995; Cronberg,1996).

Colonies of Tessellaria are primarily spherical inshape, contain a few to several hundred compactedcells, range in size from 25 to 200 μm, and have a spin-ning swimming motion (Tyler et al., 1989). As previ-ously noted, the entire colony is enclosed in multiplelayers of siliceous scales (Fig. 3F) that appear in LM as a “halo” around the colony (Fig. 2C; Tyler et al.,1989). Individual cells lack scales and are elongatedwith long cytoplasm tails that attach the cells to a ring-like structure in the center of the colony (Tyler et al.,1989). The ringlike structure is best observed with high magnification on squashed specimens. To date,Tessellaria is known only from Australia (Tyler et al.,1989; Pipes and Leedale, 1992; Lavau et al., 1997).

Colonies of Synura are typically described as beingspherical (Fig. 1I) or elongated (Fig. 1G and H) indesign and consisting of pyriform or club-shaped cells(Figs. 1F and I, and 3H; Petersen and Hansen, 1956,1958; Takahashi, 1978; Wee, 1982). There is, however,considerable variation with regard to cell and colonysize and shape, rendering such characters of little or notaxonomic value at the species level (Petersen andHansen, 1956). Within a given species of Synura,colonies with a few cells often, but not always, havemore spherical-shaped cells (Takahashi, 1978; Caladoand Rino, 1994). However, as the number of cells inthe colony increases, the cells become distinctly morepyriform or club-shaped (Fig. 3H). As noted by Petersen

526 Peter A. Siver

FIGURE 2 Light micrographs of additional synurophycean genera.A and B. Two-celled colonies of Chrysodidymus. Scale bar for A = 20μm and for B = 5 μm. The arrows denote layers of scales around thecolony. Scale bar = 50 μm. Reprinted from Graham et al. (1993) withpermission of The Journal of Phycology. C. Colony of Tessellaria.Reprinted from Tyler et al. (1989) with permission.

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14. Synurophyte Algae 527

FIGURE 3 Examples of whole cells or colonies as observed with SEM. A. Cell of Mallomonas transsylvanicawhere the bristles are distributed over most of the cell. Note the modified anterior scales from which the flagel-lum emerges. Scale bar = 5 μm. B. Cell of Mallomonas lychenensis viewed from the posterior end. Scale bar = 5μm. C. Cell of Mallomonas dickii with diamond- or rhomboid-shaped body scales and distinctly shaped collarscales that surround the flagellar opening. A very short bristle is associated with each collar scale. Scale bar = 2μm. Reprinted with permission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy andEcology. Copyright © 1991, Kluwer, Dordrecht. D. Spindle-shaped cell of Mallomonas akrokomos with a longcaudal tail. Bristles are restricted to the anterior end. Scale bar = 5 μm. E. Close-up of the anterior end of a cellof Mallomonas tonsurata depicting the flagellar opening lined with eight domed scales. Scale bar = 1 μm.Reprinted from Siver and Glew (1990) with permission. F. Colony of Tessellaria volvocina. Note that the scalesform a layer around the entire colony, not individual cells. Arrows denote flagella and arrowheads denotespined scales. Scale bar = 5 μm. Reprinted from Tyler et al. (1989) with permission. G. Close-up of a colony ofSynura petersenii depicting the spiral rows of scales around individual cells in the colony. Scale bar = 5 μm. H.Club-shaped cell of Synura petersenii that had become detached from a colony. Note the long caudal tail.Compare this image with cells in Figure 1I. Scale bar = 10 μm.

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and Hansen (1956), and illustrated by Takahashi(1978), cells that become dissociated from intactcolonies, which commonly occurs in collections, oftenchange shape and become spherical in nature. Coloniesof Synura petersenii, S. spinosa, S. sphagnicola, and S. echinulata are commonly 30–40 μm in diameter(Takahashi, 1978; Siver, unpublished data), whereascolonies of S. uvella are typically over 200 μm in diam-eter (Siver, unpublished data) and have been observedas large as 400 μm in diameter (Korshikov, 1929). Inaddition to forming spherical colonies, Synura spinosaoften forms elongated colonies (Fig. 1G and H;Takahashi, 1978; Siver, 1987). Extremely elongatedcolonies of S. spinosa, originally described as Chloro-desmus (Calado and Rino, 1994), also have beenobserved in North America (Fig. 1H). Thus, althoughcolony size and shape should not be the sole characterson which to base species determinations, tentative identifications of S. uvella and S. spinosa often can bemade based on the large colony size and formation ofdistinctly elongated colonies, respectively. Synura is avery common, widely observed, and cosmopolitangenus observed in collections throughout NorthAmerica (e.g., Nicholls and Gerrath, 1985; Siver,1987).

The distinct golden color is a result of the comple-ment of chloroplast pigments, including chlorophyll-c1,but not chlorophyll-c2, and particularly fucoxanthin(Andersen and Mulkey, 1983; Andersen, 1987). Chloro-plasts possess thylakoids in groups of three, girdlelamella, and additional external membranes referred toas the chloroplast endoplasmic reticulum (CER) orperiplastid endoplasmic reticulum (PER). A large Golgicomplex is observed below the flagallar basal bodies(Hibberd, 1978; Beech and Wetherbee, 1990a). A single, rather large nucleus is situated below the Golgiapparatus and between the chloroplasts (Beech andWetherbee, 1990a). Although evidence suggests thatthe outer membrane of the nucleus may be confluentwith the CER in Synura (Mignot and Brugerolle,1982), it appears to be, at best, weakly developed(Hibberd, 1978; Andersen, 1985). Synurophytes lackeye spots (Moestrup, 1995) and often contain a largechrysolaminarin storage vacuole in the posterior end ofthe cell; both of these features can be noted with lightmicroscopy.

Synurophytes are heterokont algae that possess along pleuronematic or tinsel flagellum and a smaller,often highly reduced, acronematic or smooth flagellum(Belcher, 1969; Hibberd, 1976; Moestrup. 1995). Inthe case of Mallomonas splendens, the second flagel-lum is lacking altogether. The tinsel flagellum bearstwo rows of tripartite hairs, and both flagella may becovered with organic scales (Moestrup, 1995). The

tinsel flagellum moves the cell forward (Belcher, 1969;Wee, 1982) by beating in an S-shaped fashion in a single plane (Jarosch, 1970). In colonial forms thesmooth flagellum beats in a more helical motion andprovides rotational movement.

As reviewed by Moestrup (1995), the basal bodiesof synurophytes range from being parallel to oneanother to being positioned at an angle of about 20°,and are connected by two or three fibrous bands. A rhizoplast originates at the base of the flagella, extendsdown along the nuclear membrane, and, at least inMallomonas splendens, becomes splayed into numer-ous branches that form an inverted cone over thenucleus (Beech and Wetherbee, 1990a). The arrange-ment of microtubular roots associated with the flagellar basal bodies has been well studied. The R1

microtubular root, which originates from the rhizoplastand forms a clockwise loop around the basal bodies, isfound in all genera (Andersen, 1985, 1987; Beech andWetherbee, 1990a; Pipes et al., 1991; Graham et al.,1993). The R3 root appears to be present only in somegenera, and the R2 and R4 roots are apparently lackingaltogether (Andersen et al., 1999).

B. Scale and Bristle Anatomy

All species of synurophytes possess a cell coat orcovering composed primarily of siliceous scales. Thedesign of the scale is species-specific and is used toidentify each taxon. There are a number of differenttypes of scales including apical, body, caudal, domed,domeless, and spined (Fig. 4). Other scale types, suchas the winged scales on Mallomonas pseudocoronata(Fig. 9B), are rarer and found on a limited number ofspecies. The cell covering of most species has morethan one type of scale, and each type is found in aspecific location on the cell coat (e.g., Fig. 3C). Apical,body, and caudal scales are positioned on the anterior,middle, and posterior portions of the cell, respectively.Spines are extensions of the front, or distal, end of thescale. Spined scales are found in all genera, but not onall species, whereas domed and domeless scales aretypes of scales found exclusively in Mallomonas.

In most cases, scales of synurophytes possess abase plate and an upturned rim (Fig. 4). The base plateis typically perforated with minute pores that may beevenly spaced, more dense in specific areas, or lackingaltogether in certain regions (e.g., flanges and the domeregion). The perforations of Chrysodidymus scales aregenerally larger and often of different diameters on thesame scale (Fig. 6A). At least part of the edge of anyscale is always turned up and bent over the base plate,forming a rim (Fig. 4A–F). For the majority of taxa, therim is situated on what is referred to as the proximal

528 Peter A. Siver

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14. Synurophyte Algae 529

FIGURE 4 The parts of a scale. A. Simple scale of Mallomonas caudata with a shield (1) and a posterior rim(4). Scale bar = 2 μm. B. Scale of Mallomonas elongata with a shield (1), dome (3), V rib (5), anterior submar-ginal ribs (7), posterior flange (6), and a posterior rim (4). The arms of the V rib (5) are continuous with thoseof the anterior submarginal ribs (7). This scale type lacks any secondary structure on the shield or flangeregions. Scale bar = 2 μm. Reprinted with permission from P. A. Siver, The Biology of Mallomonas;Morphology, Taxonomy and Ecology. Copyright © Kluwer, Dordrecht. C. Scale of Mallomonas acaroides var.muskokana with a shield (1), dome (3), V rib (5), posterior flange with ribs (6), and a posterior rim (4). Scalebar = 2 μm. D. Domeless scale of Mallomonas duerrschmidtiae possessing a shield with a well developed sec-ondary layer of large pores (2), a V rib (5) with arms that extend and become continuous with the anteriorsubmarginal ribs (7), a large posterior rim (4) that covers most of the posterior flange, and a small anteriorflange (8). Scale bar = 1 μm. E. Scale of Synura petersenii var. praefracta with a well developed thorn or keel(9), a series of ribs running from the keel to the perimeter of the scale (13), and a posterior rim (4). Scale bar =1 μm. F. Three scales of Synura echinulata each with a well developed secondary layer on the distal end of thescale (11) where the spine (10) originates, a series of short perpendicular ribs on the distal end (12), and a pos-terior rim (4). Scale bar = 2 μm.

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end of the scale and is referred to as the posterior rim.The region of a scale opposite of the proximal end isreferred to as the distal end. The posterior rim generallyencircles roughly half of the scale (e.g., Fig. 4B–D),although on scales of some Synura species (e.g., S.sphagnicola and S. lapponica) and Tessellaria, the rimmay encircle most or all of the scale. The surface of thescale that consists solely of base plate perforations andis in contact with the cell membrane is referred to asthe inner or ventral surface. The side of the scale withthe rim that faces away from the cell membrane is theouter or dorsal surface.

The majority of synurophytes have scales withadditional or secondary layers of silica deposited onthe base plate in species-specific designs, as well asother siliceous structures (Fig. 4C and D). In general, asecondary layer in Synura is composed of a siliceouslayer with pores that are larger than those on the baseplate and a series of siliceous ribs or struts. The largerpores of the secondary layer on Synura scales arerestricted primarily to the distal end of the scale. Scaleson the anterior portion of most Synura cells possess aspine, an additional diagnostic structure that protrudesfrom the base plate. For most Synura taxa the spineoriginates on the distal end of the scale and protrudesforward, away from the base plate (Fig. 4F); these taxaare in the Spinosae group. On taxa in the sectionPeterseniae the spine, more commonly referred to as akeel or thorn (Wee, 1982, 1997), originates along andis fused to the base plate (Fig. 4E). Scales of S. lapponi-ca lack spines, but possess a large centrally positionedpapillae (Fig. 10G) that is not homologous with thespine of other Synura taxa (Wee, 1997). Spines on scalesof Chrysodidymus also originate on and protrude fromthe distal end of the scale (Fig. 6A).

Many species of Mallomonas possess scales thatare considerably more complex than those of othersynurophyte genera because of the presence of highlyornamented secondary layers, V ribs, anterior sub-marginal ribs, and domes (Fig. 4C and D). The V rib isa prominent V-shaped ridge of silica positioned on thescale such that the base of the V lies in the proximalregion and the arms of the V rib extend toward the distal end of the scale, often terminating near the midsection of the scale and close to the perimeter(Figs. 4B and C, and 7B). In some cases, the arms ofthe V rib extend to the base of the dome (e.g., Fig. 9F).Many scales also possess two additional siliceous ribs,known as anterior submarginal ribs (Fig. 4B and D),that originate near the ends of the V-rib arms, run parallel to the margin of the scale, and terminate in thedistal region of the scale. On spined scales the anteriorsubmarginal ribs often fuse and become extended toform the spine.

The V rib and the anterior submarginal ribs, collectively referred to as the submarginal rib (Siver,1991a), serve to divide the scale into distinct regions.The regions bounded on the inside and outside of thesubmarginal rib are referred to as the shield and theflange, respectively (Fig. 4). The flange is further dividedinto posterior and anterior flanges. The posteriorflange is the region between the V rib and the posteriorrim, whereas the anterior flange is that portion of thescale between the anterior submarginal rib and themargin of the scale. The secondary ornamentation ofthe shield and flange areas often is quite different, andmay include pores, ribs, and papillae (Figs. 6–9).

A dome is a raised portion of the distal end of thebase plate (Fig. 4B and C) under which the proximalend of a bristle is fitted in a ball and socket fashion.Generally, scales with a dome are associated with a single bristle that emerges from an inverted U-shapedopening along the distal end of the dome. The U-shaped opening is situated to the right of center,imparting a slight asymmetry to the scale. The domeoften is ornamented with secondary structures such asribs and papillae, which are of taxonomic significance(e.g., Figs. 6C and 9C).

Scales of all Chrysodidymus and Synura species,except S. lapponica, have a more or less bilateral symmetry. Although the dome, V rib, and posterior rimmay impart slight asymmetries to Mallomonas scales,scales in this genus also have essentially a bilateral sym-metry. Scales of S. lapponica and Tessellaria are oval tocircular in design with a biradial symmetry.

The siliceous bristles, found only on cells of Mallomonas, are produced within the cell indepen-dently of scales, but become associated with the latterwhen the cell covering is constructed. A bristle can be divided into the foot and shaft (Siver, 1991a). Thefoot consists of the proximal end of the bristle that is slightly bent relative to the long shaft and tuckedunder the dome. The shaft often is slightly bowed,smooth or ribbed, and serrated; the teeth of the serra-tion may be along most of the shaft or restricted to the distal end. The morphology of the distal ends of bristles is highly variable between species and is oftaxonomic importance (Siver, 1991a). Tips are com-monly blunt, drawn out into sharp points, bifurcate, or expanded to form a C-shaped or cleftlike openingknown as a helmet (e.g., M. acaroides v. muskokana)or hooked (e.g., M. heterospina) bristle. Species commonly possess either one or two types of bristlesthat are generally found on different positions of the cell. Typically, a smaller type of bristle is asso-ciated with the apical scales, and a longer and morpho-logically distinct type of bristle is allied with bodyscales.

530 Peter A. Siver

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C. Arrangement of Scales on the Cell Surface

Except for Synura lapponica and Tessellaria, scaleson all synurophytes are arranged on the cell surface in well-ordered, overlapping, spiral rows (Leadbeater,1986, 1990; Siver and Glew, 1990; Graham et al.,1993). As noted by Siver and Glew (1990), if the scalesare traced in a row from the posterior to the anterior ofthe cell, the rows of scales always appear to be spiraledto the right (e.g., Fig. 3B). In Mallomonas and Synura,the scales within a given row are overlapped in a posterior to anterior manner; that is, each scale is overlapped by the scale positioned behind it in thesame row (Siver and Glew, 1990). The only knownexception to this rule is M. retrorsa, and most likely M. fenestrata, where the orientation of scales on thecell surface is reversed (Siver, 1988b, 1991a).

In all Mallomonas taxa except M. akrokomos, thespiral rows of scales overlap each other in an anteriorto posterior manner (Fig. 3B). However, in Synura therows of scales are overlapped in a posterior to anteriormanner (Figs. 13G and H). Thus, for most Mallomonastaxa, a given scale is overlapped by the scale positionedbehind it in the same row and by scale(s) in the rowanterior to it. For Synura species, a given scale is over-lapped by the scale behind it in the same row and byscale(s) in the row posterior to it. The complexity ofthe scale coat on Chrysodidymus cells has not yet beendescribed.

Within a given row, scales are orientated such thattheir distal ends point (a) toward the anterior of the cell (parallel arrangement), (b) at 90° to the right(perpendicular arrangement), or (c) at an intermediateposition (oblique arrangement; Leadbeater 1986; Siver and Glew, 1990). Mallomonas retrosa is the onlyknown exception to this arrangement and orientationof scales. The number of spiral rows of scales on a cell is equal to the number of scales that surround theflagellar pore, and the number of scales in any row on agiven cell is approximately equal (Siver and Glew, 1990).

Each spiral row of scales on a cell of Mallomonasor Synura begins with an apical scale that is part of thering of scales that encircles the emergent flagella(um),grades into body scales, and terminates with posterioror caudal scales. The change in scale type within a spiral row may be gradual, as in Synura (Wee, 1997)and many species of Mallomonas (Asmund andKristiansen, 1986; Siver, 1991a), or very abrupt, as insome sections of Mallomonas (e.g., section Torquatae).On Synura cells, the spines or keels on scales graduallydiminish in length or height from the anterior to theposterior of the cell, and are either minute or lackingon the posterior-most portions of the cells. On cells of Chrysodidymus, although the length of scales alsodiminishes toward the posterior end of the cell, all

scales possess spines (Nicholls and Gerrath, 1985). Thelack of spines on posterior portions of Synura cells maybe related to the fact that cells in the colony are indirect contact with each other, a condition not found intwo-celled Chrysodidymus colonies.

The formation and subsequent deployment ofscales and bristles onto the cell surface in Mallomonasand Synura have been summarized by Leadbeater and Barker (1995), Wetherbee et al. (1995), and Wee(1997). A brief synopsis is provided here. Individualscales and bristles form within specialized vesiclesknown as silica deposition vesicles (SDVs) that aremost likely derived from the Golgi complex (McGroryand Leadbeater, 1981; Mignot and Brugerolle, 1982).Initially, the SDV becomes positioned along the outerand anterior surface of the PER of one of the chloro-plasts (Belcher, 1969; Mignot and Brugerolle, 1982).Microtubules (Mignot and Brugerolle, 1982; Leadbeater,1986) and actin-like microfilaments (Brugerolle andBricheux, 1984; Leadbeater and Barker, 1995) becomeassociated with the SDV and may aid to shape and tomove the SDV in a helical pathway down along thePER (Mignot and Brugerolle, 1982). As the SDV istransported along the outer surface of the chloroplast,it is flattened and molded into the shape of a scale.Once the mold of the scale is completed, silica isdeposited to produce the finished product (Wujek andKristiansen, 1978; Mignot and Brugerolle, 1982;Leadbeater, 1990).

Bristles are formed in a similar fashion to scales,but in separate SDV vesicles and apparently at differenttimes (Wujek and Kristiansen, 1978; Mignot andBrugerolle, 1982; Beech et al., 1990). Once a scale orbristle is formed, the SDV moves toward and fuseswith the cell membrane, resulting in release of thesiliceous component onto the outer surface of the cell.Although the precise mechanism(s) by which the scalesand bristles are maneuvered into place remains unclear,hypotheses have been proposed for cells with existingscale coats (Leadbeater 1990; Beech et al., 1990) andfor naked cells (Siver and Glew, 1990). Scales and bristles are held in place by an adhesive material(Leadbeater, 1986; Wetherbee et al., 1995).

D. Cysts, Life Cycle, and Cell Division

All synurophytes are believed to form a siliceousresting stage known as a cyst, a stomatocyst, or astatospore (Fig. 5). Cysts can be produced as a result ofasexual or sexual reproduction (Skuja, 1950; Cronberg,1986; Sandgren and Flanagin, 1986; Sandgren, 1988,1991), and their formation may be triggered by suddenchanges in environmental conditions (Cronberg, 1980, 1986; Sandgren, 1981) or population density

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532 Peter A. Siver

FIGURE 5 Features of cysts. A. Intact cell of Mallomonas punctifera that is encysted as viewed from the ante-rior end. Scale bar = 2 μm. B. Cell of Mallomonas acaroides var. muskokana containing a partially formed cystwith a reticulated surface. Scale bar = 2 μm. C. Close-up of part of a cell of Mallomonas tonsurata with a fullyformed cyst. Note spines with splayed tips. Scale bar = 1 μm. D. An immature cyst where the bases of spines(circular structures) have just begun to form. Scale bar = 5 μm. E. Remains of cysts of various sizes anddesigns. All three cysts possess spines. The two larger cysts also have scabrae (small bumps) and the smallercyst depressions or tangential circuli. Scale bar = 5 μm. F. A cyst with a smooth surface, long spines, and asmall pore surrounded by a collar. Note the small cyst with ridges that form a regular reticulum. Scale bar =5 μm.

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(Sandgren, 1988). Even though hundreds of cyst mor-photypes have been observed, only a small percentagehave been linked to actual species (Duff et al., 1995).

Cysts are hollow structures that generally are globose in shape, have a single germination pore, andare formed endogenously within a silica SDV (Preisigand Hibberd, 1982a, b; Sandgren, 1991). The SDVencloses the nucleus, chloroplasts, Golgi apparatus,storage material, and a large volume of the cytoplasm(Cronberg, 1986; Sandgren, 1989). The formation ofthe wall of the cyst is a continuous process that takesplace within the SDV in what is believed to be a two-step process (Skogstad, 1984; Sandgren, 1989).The inner, or primary, wall forms first in a rather rapidfashion, and results in a wall that is usually unorna-mented and morphologically similar in many species(Duff et al., 1995). For many species, the primary wallis also distinctly different in appearance from themature cysts (e.g., Fig. 5B; Skogstad, 1984; Siver,1991c). Additional cyst wall layers, including the wallornamentation and the collar, form in a slower andmore controlled manner on the outer surface of the primary wall (Fig. 5D). As the cyst wall is being completed, the pore becomes plugged, usually with anorganic material. It is unknown if an immature cyst, inthe sense of lacking a fully ornamented wall, is viable.

Duff et al. (1995) provided an excellent summaryof the terminology associated with the description ofcysts. Cysts range in size from ca. 2 to > 30 μm(Sandgren and Carney, 1983; Duff et al., 1995), rangein shape from spherical to oval to a flat, pancake form,and vary in design from smooth (e.g., Fig. 5F) to highlyornamented (e.g., Fig. 5E). The body of a cyst is divided into anterior and posterior hemispheres, andthe pore is located in the anterior hemisphere. The poreis circular and may or may not be surrounded by athick rim of silica called the collar (Fig. 5E and F).Collars may be simple or complex, the latter consistingof two or more separate collars that surround the porein a concentric fashion. The morphology of the outerwall and the pore–collar complex is of taxonomicimportance (Sandgren and Carney, 1983; Skogstad,1984; Sandgren, 1989). A multitude of ornamentationsis associated with the mature cyst wall, including nod-ules, spines, ridges, circular ridges (circuli), depressions,and various types of reticulations (Fig. 5).

Vegetative cells and cysts formed through asexualprocesses are believed to be haploid. Cysts formed bysexual reproduction have two separate and presumablyhaploid nuclei after cellular fusion; nuclear fusion andmeiosis occur upon germination of the cyst (Sandgren,1991). Sexual reproduction is isogamous and fusion ofgametes in several species of Mallomonas has beenobserved to be the result of contact by either the caudal

or apical ends of cells (reviewed in Wee, 1982, andAsmund and Kristiansen, 1986). Cytokinesis inMallomonas occurs along the longitudinal axis, begin-ning from the anterior end, and is completed withinminutes (Harris, 1953; Wawrik, 1979; Beech andWetherbee, 1990b; Beech et al., 1990).

Colonies of Synura and Tessellaria also divide bybinary fission. Colonies of Synura, but not Tessellaria,may elongate prior to division, and in both genera theresultant daughter colonies are not necessarily com-posed of equal numbers of cells. In Tessellaria, Tyler et al. (1989) noted the formation of a furrow channelaround the colony that eventually grew deeper andyielded the two daughter colonies.

E. Taxonomic and Phylogenetic Considerations

Species within the genera Synura and Mallomonasare grouped into sections and series based primarily onultrastructual features of the scale covering (Momeuand Péterfi, 1979; Asmund and Kristiansen, 1986;Siver, 1991a; Wee, 1997). Petersen and Hansen (1956,1958) originally proposed three sections for the genusSynura: Lapponica, Peterseniae, and Synura. The sec-tion Lapponica consists of only one species, S. lapponi-ca (Fig. 10G), whereas those taxa with scales thatpossess either a keel or a spine are positioned withinsection Peterseniae or section Synura, respectively.Later, Péterfi and Momeu (1977) divided taxa withinthe section Synura into two series, Synura andSplendidae, based on the presence or absence, respec-tively, of secondary structures on the scales. Wee(1997) presented a slight modification of this taxonom-ic grouping. There are at least 27 described species andsubspecific taxa within the genus Synura (Nicholls andGerrath, 1985; Siver, 1987, 1988c; Cronberg, 1989),roughly half of which commonly are observed in NorthAmerica (Nicholls and Gerrath, 1985; Siver, 1987).

Harris and Bradley (1957, 1960) originally dividedMallomonas into four series, Tripartitae, Planae,Quadratae, and Torquatae, based primarily on theultrastructure of scales as observed with both light and electron microscopy. Momeu and Péterfi (1979)later raised the four series to the rank of section. Sincethat time, the taxonomy of Mallomonas has relied progressively more on structures observed with electron microscopy, and there are now over 116species (Moestrup, 1995) in 17 sections (Asmund andKristiansen, 1986; Siver, 1988b). Most recently, Péterfiand Momeu (1996) used cluster analysis based on phenetic ultrastructural features of scales and bristlesto further modify the genus Mallomonas.

The anatomy of the siliceous scales and their orientation on the cell surface clearly indicate that

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Chrysodidymus belongs in the Synurophyceae. Grahamet al. (1993) further demonstrated that the genusshared many cellular and ultrastructural characterswith other synurophytes, supporting its inclusion in the Synurophyceae. However, the validity of the genusChrysodidymus, as well as the described species, havebeen questioned. Prowse (1962) originally describedtwo species of Chrysodidymus, C. synuroideus and C.gracilis, that were differentiated on the basis of cell sizeand shape. Later, Wujek and Wee (1983) suggested,and Graham et al. (1993) concluded that the twospecies described by Prowse (1962) should be com-bined into one, C. synuroideus. The more importanttaxonomic question concerned the validity of the genus.Even though the scales of Chrysodidymus are clearlySynura-like, the genus Chrysodidymus has been retainedon the basis of the two-celled nature of the colony. Thework of Graham et al. (1993) clearly demonstratedthat Chrysodidymus consists solely of two-celledcolonies and has several unique ultrastructural charac-ters, supporting separation from the genus Synura.

Much work is needed on phylogenetic relation-ships of the Synurophyceae relative to other groups ofheterokonts, especially the Chrysophyceae (Andersen et al., 1999). In their monograph on Mallomonas,Asmund and Kristiansen (1986) considered specieswith scales that lacked domes and secondary struc-tures, that had smooth and bifurcate bristles, and thathad cells with two emergent flagella as ancestral. Thus,although their classification system is perhaps some-what artificial, their treatment of taxa attempted toprovide phylogenetic relationships between a diversearray of organisms. Péterfi and Momeu (1996) alsoprovided some indication of the relationships betweentaxa within the genus Mallomonas, but recognized thattheir use of numerical taxonomy based on pheneticcharacters may not yield true phylogenetic relation-ships, a point discussed by Wee (1997).

Despite the need for additional work, five observa-tions on phylogenetic relationships can be made basedon the works of Wee (1997) and Lavau et al. (1997).

1. The Synurophyceae appears to be monophyletic(Lavau et al., 1997).

2. Both Wee (1997) and Lavau et al. (1997)concluded that Tessellaria volvocina is at thebase of the Synurophyceae lineage, and Wee(1997) further pointed out that S. lapponica isclosely allied with Tessellaria volvocina (Wee,1997), a hypothesis also supported by Tyler etal. (1989). In fact, Petersen and Hansen (1958)suggested that S. lapponica be removed from thegenus Synura because of the biradial symmetryof its scales and the fact that the scales were

most likely arranged in multiple layerssurrounding the entire colony and not onindividual cells.

3. The study by Lavau et al. (1997), which utilizedboth scale and molecular data, weaklysupported both Synura and Mallomonas asmonophyletic groups. However, the authorspointed out that when used separately, neitherthe scale ultrastructure data nor the moleculardata were able to resolve Synura as amonophyletic unit, and likewise the moleculardata alone were not able to resolve Mallomonasas monophyletic. In addition, the phylogenyproduced by Wee (1997) had M. caudata and S. petersenii emerging from the same cladewithin the section Synura, and he concludedthat more work was needed to determine ifMallomonas was a monophyletic genus.

4. Chrysodidymus synuroideus appears to beancestral to the series Synura, those taxa withscales that have emergent spines and secondaryornamentation (Wee, 1997). On the other hand,Wee (1997) observed that S. sphagnicola wasremoved from other Synura taxa with spines,including S. splendida, and was less allied withChrysodidymus than suggested by Graham et al.(1993).

5. As proposed by Asmund and Kristiansen(1986), both Lavau et al. (1997) and Wee(1997) concluded that morphological charactersof scales are important and very useful forresolving relationships at the genus, species, andsubspecific levels.

III. ECOLOGY AND DISTRIBUTION

A. General Comments

The Synurophyceae are euplanktonic in nature andoccur almost exclusively in freshwater habitats.Although a large number of species in the Chryso-phyceae are known mixotrophs (Andersen et al.,1999), members of the Synurophyceae are believed tobe strict photoautotrophs (Salonen and Jokinen, 1988;Holen and Boraas, 1995). They are most commonlyencountered in plankton from ponds and lakes,although substantial numbers also can be found inlarge slowly flowing rivers, as well as in pools in smaller streams (e.g., Dürrschmidt, 1980; Siver andVigna, 1997). Generally, taxa of Synurophyceae can becollected in most samples from lacustrine locationsduring any season, and it is not uncommon to find 10or more different species from a single collection(Jacobsen, 1985; Siver and Hamer, 1989; Eloranta,

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1989; Siver, 1991a; Wee et al., 1993). Over 50 speciesof Synurophyceae were observed over an annual cyclein a single water body (Siver and Hamer, 1992).

Synurophytes are often observed as components of deep-water metalimnetic algal peaks that developduring stratified periods (e.g., Pick et al., 1984; Pickand Cuhel, 1986; Hoffman and Wille, 1992). Taxa of Synura and Mallomonas, as well as other colonialscaled chrysophytes, can dominate metalimneticregions of stratified lakes, may account for over 90%of the phytoplanktonic biomass (Hoffman and Wille,1992), and form densities well above those found insurface waters (Barbiero and McNair, 1996). Suchdeep-water layers can form by in situ growth, passiveaccumulation from the epilimnion, or active migrationfrom surface waters, and can be overlooked in routinesampling efforts. Generally, a decrease in the amount oflight reaching the metalimnion, depletion of a nutrient,or vernal mixing results in the disruption of such peaks(Barbiero and McNair, 1996).

Species of Mallomonas and Synura, including M.crassisquama, M. caudata, S. uvella, and S. petersenii,are known to form blooms (Clasen and Bernhardt,1982; Nicholls and Gerrath, 1985; Hoffman and Wille,1992), and blooms of Synura are often associated withtaste and odor problems (Wee et al., 1994; Nicholls,1995). Water tainted with a fishlike odor caused bysynurophyte blooms is reported from both soft- andhard-water lakes, and often results in the need to treatthe water before consumption by humans (Nicholls,1995). Although, historically, many taste and odorproblems have been attributed to S. uvella, mostepisodes are probably caused by S. petersenii (Nichollsand Gerrath, 1985; Wee et al., 1994).

Although members of the Synurophyceae are well documented from many temperate, subtropical,and tropical localities (Nicholls and Gerrath, 1985;Kristiansen, 1986; Cronberg, 1989; Wee et al., 1993),there is some evidence that they diminish in diversityand biomass in subarctic and arctic regions of both thenorthern (Kristiansen, 1992) and southern (Croomeand Tyler, 1988) hemispheres. In fact, Croome andTyler (1988) did not find a single taxon after examina-tion of many samples from subarctic and arctic islandsfrom the southern hemisphere, and scales are oftenvery scarce in sediment samples from northern arcticponds (J. Smol, Queens University, personal commmu-nication). Most in-depth surveys of the Synurophyceaefrom North America indicate a well developed, temper-ate flora, but a tropical element has been described inworks from Florida (e.g., Siver and Wujek, 1993) andLouisiana (Wee et al., 1993).

Most, but not all, taxa found in North America are cosmopolitan in nature and have been reported

on other continents. Synura petersenii (Siver, 1987),Mallomonas caudata (Siver, 1991a), and M. crassisqua-ma (Siver and Skogstad, 1988, and references therein)are among the most common synurophytes found inNorth America and around the world. A few taxa,however, are known to have restricted geographicranges. One taxon in particular, Mallomonas pseudo-coronata, is a common taxon found almost exclusivelyin North American waters (Siver, 1991a). Mallomonasduerrschmidtiae, M. acaroides var. muskokana, and, toa lesser extent, M. galeiformis are other commonlyencountered species in the northeastern part of NorthAmerica, especially in dilute soft-water lakes, but rarely are reported in other regions of the world (Siver,1988d, 1991a; Siver et al., 1990; Nicholls, 1987,1988a, b).

Because of their limited distributions along variousenvironmental gradients, many species of synurophytesare excellent bioindicators (Kristiansen, 1986; Siver,1995; Smol, 1995). Some species are known primarilyfrom warm or cold water, acidic or alkaline conditions,and oligotrophic or eutrophic habitats. Many taxa arelimited by the specific conductance of the water (Siver,1993), and others appear to be sensitive to high con-centrations of metals (Gibson et al., 1987; Dixit et al.,1989). As a result of the differential distributions ofspecies along various gradients and the fact that the species-specific siliceous scales or cysts become preserved in lake sediments, the Synurophyceae havebecome a very valuable organismal group for recon-structing past lake-water conditions (Smol, 1995; Siveret al., 1999).

B. Primary Habitat Requirements

Ecological studies of the Synurophyceae oftenmake observations and draw conclusions that includemembers of the Chrysophyceae (Chap. 12) that havesiliceous scales (i.e., scaled chrysophytes). Therefore, itis unavoidable that much of the following discussionpertains to the scaled chrysophytes. Reviews of the ecological distributions of synurophytes along environ-mental gradients and their occurrences in blooms have been compiled by Sandgren (1988), Siver (1991a,1995), Nicholls (1995), and Sandgren and Walton(1995).

As a group, as well as for individual species,synurophytes exhibit very different tolerances alongenvironmental gradients (e.g., Siver, 1989, 1991a,1995; Siver and Marsicano, 1996; Cumming et al.,1992a). In a broad sense, Siver (1995) summarized thehabitats that support the richest floras of synurophytesas those that are slightly acidic (Siver and Hamer,1989; Siver, 1992; Wee and Gabel, 1989), are low in

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specific conductance, alkalinity, and nutrient content(Cronberg and Kristiansen, 1980; Roijackers andKessels, 1986; Siver, 1991a, 1995), and have moderateamounts of humic substances (Cronberg andKristiansen, 1980; Dürrschmidt, 1980, 1982; Wee andGabel, 1989; Siver, 1991a; Eloranta, 1995; Siver andVigna, 1997). Humic-colored lakes and ponds are typically small and shallow, located in forested areas,and often situated in watersheds that drain marsh orwetland areas (see also Chap. 2). A preference forhumic-stained localities may explain the commonobservation that scaled chrysophytes are typically moreabundant in smaller ponds (Dürrschmidt, 1980;Kristiansen, 1981; Cronberg, 1989).

The chrysophytes, including the synurophytes, longwere considered to be a group that was primarilyrestricted to cold, oligotrophic habitats and occurredprimarily in the spring (Siver, 1995, and referencestherein). However, more recent studies from warmregions of the world dispute this hypothesis (e.g.,Takahashi and Hayakawa, 1979; Kristiansen, 1980,1981, 1986; Kristiansen and Takahashi, 1982;Dürrschmidt and Croome, 1985; Cronberg, 1989; Sahaand Wujek 1990; Siver and Wujek 1993, Siver andVigna 1997). In North America, rich and diverse florasof synurophytes have been documented from subtropi-cal localities in Florida (Wujek, 1984; Wujek andBland, 1991; Siver and Wujek, 1993) and Louisiana(Wee et al., 1993). Similarly, even though scaled chrysophytes comprise a larger percentage of the annual phytoplanktonic biomass of oligotrophic andmesotrophic lakes (see subsequent discussion), amplestudies demonstrate that large numbers of species alsocan be found in more eutrophic sites (Kristiansen,1985, 1988b; Hickel and Maass, 1989; Gutowski,1989, 1997; Saha and Wujek, 1990). For example,Kristiansen and Tong (1989) and Kristiansen (1985)recorded 40 and 33 taxa of scaled chrysophytes inhighly eutrophic ponds in China and Denmark, respec-tively. Gutowski (1989) and Hickel and Maass (1989)observed over 23 taxa of scaled chrysophytes in nutrient-enriched sites in Germany. In North Americanlocalities, Siver and Hamer (1989) found no significantdifference in the number of taxa sampled from along a total phosphorus gradient, further supporting thehypothesis that large numbers of synurophyte taxa arecapable of growing in nutrient-enriched waters. Inaddition, although synurophytes are commonly knownto comprise a significant portion of vernal blooms, theyalso can be important components of the flora in summer, autumn, and winter periods (Dürrschmidt,1980; Siver and Chock, 1986; Kristiansen, 1986; Siver, 1991a; Siver and Hamer, 1989; Sandgren, 1988;Nicholls, 1995).

C. Distribution along a pH Gradient

Lakewater pH repeatedly has been demonstratedto be a primary factor that controls the distribution of synurophytes in freshwater localities (Siver, 1995;Smol, 1995). The importance of pH has been concludedfrom numerous studies utilizing ordination techniques(e.g., Siver and Hamer, 1989), as well as from morestandard floristic surveys (e.g., Takahashi, 1978). InNorth American-based studies, pH has been demon-strated to be an important variable influence on thecomposition of scaled chrysophytes in southern NewEngland (Siver and Hamer, 1989), northern NewEngland (Dixit et al., 1990), the Adirondacks (Smol et al., 1984; Cumming et al., 1992a, b; Duff and Smol,1995), Florida (Siver and Wujek, 1999), Iowa (Weeand Gabel, 1989), and Ontario (Dixit et al., 1988).

The most diverse floras of scaled chrysophytes aretypically found at slightly acidic conditions (Siver andHamer, 1989; Siver and Smol, 1993). In a diverse arrayof habitats from Connecticut, Siver and Hamer (1989)found the largest number of species between pH 5.5and 6.5, and significantly fewer taxa below pH 5 andabove pH 8. Many species tend to disappear and mem-bers of the group as a whole becomes less abundant asthe pH drops below 5 (Siver, 1989, 1991a; Hartmannand Steinberg, 1989). Based on a thorough literaturesearch, Siver and Smol (1993) observed a similar pattern for the number of synurophyte species along apH gradient, which suggests that the effect of pH issimilar in different regions of the world. Although notcommon, large numbers of species have been reportedfrom more alkaline, high-pH habitats (e.g., Gutowski,1989; Hickel and Maass, 1989), especially if the humiccontent is high (Siver and Wujek, 1993).

Many synurophyte species have definitive and well-documented distributions along a pH gradient,and many taxa have been characterized by the pH categories defined by Hustedt (1939; see Takahashi,1978; Siver, 1989, 1991a, 1995; Smol, 1995). Based ona review of the literature, Siver (1989) concluded thatmany species have similar distributions along a pHcontinuum and similar weighted mean pH values inwidely separated geographic regions. Further, based on the review by Siver (1989), Siver and Smol (1993)identified four groups of scaled chrysophytes that hadsimilar distributions relative to pH gradient. A low-pHgroup of taxa included Mallomonas canina, M.hindonii, M. paludosa, M. pugio, M. hamata, M.acaroides var. muskokana, Synura sphagnicola, and S.echinulata. Taxa in this group are consistently observedbelow pH 6, have abundance weighted mean pH(AWMpH) values of less than 6, and are primarily aci-dobiontic organisms (see Siver, 1995). Chrysodidymus

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synuroideus is another well-documented acidobionticspecies, often present in bogs (Graham et al., 1993),that is reported to have an AWMpH of 4.6 (Dixit et al.,1988) and 5.5 (Charles and Smol, 1988).

The mid-pH group consists of species that occurmost often below pH 7, but generally above pH 5,have AWMpH values near or above 6, and are bestclassified as acidophilic (see Siver, 1995, and referencestherein). Synurophyte taxa in this group includedMallomonas galeiformis, M. heterospina, M. duerr-schmidtiae, M. punctifera, M. transsylvanica, M. dickii,M. doignonii, M. torquata, and Synura spinosa. Thethird group consists of pH indifferent species that havetheir center of distribution and AWMpH values aroundpH 7. However, many of the pH indifferent species alsocan be found at relatively high or low pH. The fourthor high-pH group consists of alkaliphilic taxa that aredistributed primarily above pH 7 and have AWMpHvalues greater than 7. The high-pH group includesMallomonas acaroides var. acaroides, M. tonsurata,M. corymbosa, M. pseudocoronata, M. elongata, M.alpina, and M. portae-ferreae. As a result of the rathernarrow distributions of many synurophytes along a pHgradient, assemblages have been successfully utilized toinfer historical lake-water pH conditions (Siver, 1995;Smol, 1995; Siver et al., 1999).

D. Distribution along a Dissolved Salt Gradient

There is now ample evidence that the concentra-tion of dissolved salts is another important factor thatcontrols the distributions of scaled chrysophytes. As agroup, the Synurophyceae are observed more frequentlyand have significantly higher species diversities in local-ities low in specific conductance (Sandgren, 1988; Siverand Hamer, 1989), and are virtually absent in salinelakes (Zeeb and Smol, 1995). Based on data from alarge and diverse array of lake types, Siver and Hamer(1989) demonstrated that specific conductance was as important as pH in explaining the occurrences ofscaled chrysophytes as well as the number of speciesfound per collection. The maximum number of speciesper collection was observed in water bodies with aspecific conductance of only ca. 40 μS cm–1, anddropped significantly as the level reached 200 μS cm–1.

Since the work of Siver and Hamer (1989), a num-ber of additional studies also have demonstrated theimportance of dissolved salt concentrations on synuro-phyte assemblages. Zeeb and Smol (1991) used scaled-chrysophyte remains in a sediment core to trace theeffects of road de-icing salts on a small lake inMichigan. The distributions of scale remains(Cumming et al., 1992a) and cysts (Duff and Smol,1995) in surface sediments of lakes in the Adirondack

Mountains of New York also have been reported to beinfluenced by dissolved salts. Siver (1993) developed an inference model that was used to trace the effects of deforestation and residential development on lake-water specific conductance levels (Lott et al., 1994;Siver et al., 1999). The physiological mechanism(s) that control the responses of specific synurophytes todissolved salt concentrations, or to specific cations oranions, remains unknown.

E. Distribution along a Trophic Gradient

Scaled chrysophytes, and most likely theSynurophyceae, often account for larger percentages ofphytoplankton biomass in oligotrophic and earlymesotrophic lakes than in more eutrophic localities(Kristiansen, 1986; Sandgren, 1988; Nicholls, 1995;Siver, 1995; Sandgren and Walton, 1995). Such a trendhas been reported from many regions of the world,including temperate and subtropical regions of North America (Kling and Holmgren, 1972; Siver andChock, 1986; Siver, 1991; Siver and Wujek, 1993),Scandinavia (Eloranta, 1989), Greenland (Jacobsen,1985), and Australia (Croome and Tyler, 1985, 1988).Based on an in-depth survey of the literature, Sandgren(1988) concluded that chrysophytes (including theSynurophyceae) often account for between 10 and75% of the biomass of oligotrophic lakes regardless ofdifferences in size, mixing pattern, and geographiclocation. Sandgren (1988) further noted that the group often comprised <20% of the biomass in moremesotrophic and eutrophic lakes, and generally <5%in very eutrophic sites. Indeed, the presence of scaledchrysophytes usually indicates that the locality is notheavily polluted (Kristiansen, 1981, 1986).

Schindler et al. (1973), Findlay (1978), andDeNoyelles and O’Brien (1978) all noted significantdeclines in chrysophyte biomass following additions ofnutrients to experimental lakes and ponds. Conversely,the relative abundance of chrysophytes often increasesfollowing management efforts to decrease the nutrientload to eutrophic water bodies (Cronberg et al., 1975; Cronberg, 1982; Nicholls, 1995). Sandgren andWalton (1995) advanced the hypothesis that the inverserelationship between the percentage of phytoplanktonbiomass composed of chrysophytes and trophic statuswas partly regulated by zooplankton predation, especially from large-bodied Daphnia. Zooplanktonfeeding patterns may also partially explain why chryso-phytes often bloom during discrete periods of the year(Sandgren and Walton, 1995). Despite the generaliza-tion that scaled chrysophytes decline with increasingeutrophy, some recent surveys from warm regions indicate that the biomass of scaled chrysophytes can be

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high, and often greatest, in eutrophic sites (Siver andWujek, 1993; Wujek and Bicudo, 1993; Yin-Xin andKristiansen, 1994; Cronberg, 1996).

At the species level, many synurophytes are differ-entially distributed along a trophic gradient (Siver,1995; Siver and Marsicano, 1996). Based on literaturerecords, Siver (1991a) recognized a group of Mallo-monas species common in North American waters,including M. duerrschmidtiae, M. acaroides var.muskokana, M. galeiformis, M. hamata, M. asmundiae,M. pugio, M. paludosa, and M. torquata, that is primarily reported from oligotrophic or mesotrophichabitats. Siver (1991a) further noted that anothergroup of species commonly reported from NorthAmerica, consisting of M. tonsurata, M. alpina,M. corymbosa, M. portae-ferreae, M. acaroides var.acaroides, M. lychenensis, and, to a lesser extent,M. elongata and M. pseudocoronata, is more commonin eutrophic localities. Mallomonas heterospina is oftenreported from dung- or waterfowl-contaminated ponds(Harris and Bradley, 1957; Kristiansen, 1986; Siver,1991a), and there appears to be ample evidence thatM. matvienkoae is also common in highly eutrophichabitats (Saha and Wujek, 1990; Siver and Vigna,1997). Synura sphagnicola (Kristiansen, 1986; Siver,1988a) and S. spinosa forma longispina (Dürrschmidt,1982; Siver, 1987) are other oligotrophic indicators,whereas S. curtispina (Gutowski, 1989; Santos andLeedale, 1993; Siver and Marsicano, 1996) is oftenobserved to tolerate eutrophic conditions. Becausespecies of scaled chrysophytes are indicative of trophicconditions, they have been useful in paleolimnologicalstudies (Smol, 1995; Siver and Marsicano, 1996; Siveret al., 1999).

F. Distribution along a Temperature Gradient

Although both Roijackers and Kessels (1986) andSiver and Hamer (1989) concluded that pH and relatedfactors were the most important variables that controlthe development of specific species in a given lake,water temperature is instrumental in determining thetime period and degree to which a population devel-oped. Gutowski (1989) and Siver and Hamer (1992)also concluded that temperature plays a key role in the development and subsequent seasonal succession of species in individual lakes, and Siver and Hamer(1992) further showed that the scaled-chrysophytecommunity could accurately infer water temperature.

Chrysophytes, including synurophytes, often domi-nate phytoplankton biomass during spring (and, to alesser extent, autumn) mixing when the water tempera-ture is low (Wetzel, 1983; Sandgren, 1988; Gutowski,1996). In a survey of 141 water bodies, Sandgren

(1988) found that the greatest biomass of chrysophytesoccurred between 10 and 20°C, and that the biomasssignificantly declined above 20°C. Other studies haveillustrated maximal concentrations of synurophytes at temperatures below 12°C (Kristiansen, 1975, 1986;Jacobsen, 1985; Siver and Chock, 1986; Hickel andMaass, 1989; Siver 1991a). Despite the fact that thebiomass of scaled chrysophytes is often found to bemaximal at low temperatures during spring mixing,Siver (1995) and Sandgren and Walton (1995) pointedout that factors other than temperature (e.g., increasednutrients and light, turbulence, and grazing) may playpivotal roles in explaining this phenomenon.

Whether water temperature is involved in regulat-ing species diversity among synurophytes is unclear.Siver and Hamer (1989) found no significant differencebetween the number of species of Mallomonas observedin a lake at a given time and water temperature, but arelationship was observed for species of Synura. Otherworks support the fact that large numbers of synuro-phyte species can be found at both low (e.g., Jacobsen,1985; Siver, 1991a) and high (Cronberg, 1989; Sahaand Wujek, 1990) water temperatures.

Regardless of the relationship between speciesdiversity and water temperature, many species and sub-specific taxa are indeed differently distributed along a temperature gradient (Siver, 1995). Siver (1991a)divided Mallomonas taxa into five groups based onabundance along a temperature gradient. The warm-water group consists of species rarely found below12°C and with abundance weighted mean (AWM) temperature values above 15°C. Cool-water taxa arespecies observed primarily between 12 and 15°C, andare less often encountered outside of this range. Thecool–cold-water species had AWM temperatures below12°C, but often are found above 15°C. The cold-waterclass consists of taxa rarely observed above 15°C andthat have AWM temperatures below 12°C. The fifthgroup, temperature-indifferent species, consists of taxaobserved along the entire temperature gradient. Speciesof Synura and Chrysodidymus synuroideus also areknown to be distributed differently along a temperaturegradient (Siver, 1995). In particular, Synura lapponica(Siver and Hamer 1992), S. echinulata (Asmund, 1968;Kristiansen, 1975; Siver and Hamer, 1992), and S.spinosa (Kristiansen, 1975; Kies and Berndt, 1984;Roijackers and Kessels, 1986) are all primarily coldwater taxa, whereas S. sphagnicola (Asmund, 1968;Kristiansen, 1975; Siver and Hamer, 1992) and C.synuroideus (Dürrschmidt and Croome, 1985) are mostoften observed during the warmer summer months.

Only a few observations to relate temperature tochanges in scale and bristle structure have been under-taken. Siver and Skogstad (1988) observed different

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types of bristles on cells of M. crassisquama at differenttemperatures and suggested that bristle type may berelated to buoyancy. Gutowski (1996) demonstratedthat scales and bristles of M. tonsurata decreased inlength as the water temperature increased. The rolethat temperature may play in the formation of cysts byeither asexual or sexual processes, as well as in theirgermination, was discussed in detail by Sandgren andFlanagin (1986) and Sandgren (1988).

IV. COLLECTION AND PREPARATION FOR IDENTIFICATION

A. Collection of Samples

The methods used to collect and concentratesynurophytes depend, in part, on the goals of the inves-tigation. Some projects require collection of samplesfrom near-surface waters, whereas others focus on samples that integrate communities throughout thephotic zone. A Van Dorn collecting bottle or someother standard device can be used to collect water fromdiscrete depths, whereas tubing is often used to makean integrated sample of the water column. For quanti-tative work, standard methods for concentrating andestimating phytoplankton communities should be used;typically, these include either centrifugation or settlingtechniques. Centrifugation of fixed samples thatinclude synurophytes is best done using low speeds of2000 rpm (Siver and Hamer, 1990) or less (Wee, 1983).Taylor et al. (1986) presented a slight modification of the standard Utermöhl settling method that isspecifically designed for scaled chrysophytes.

Wee (1983) reviewed some of the commonfixatives used to preserve and to study cells andcolonies of scaled chrysophytes. Acidified Lugol’s solution is one of the best preservatives for use withsynurophytes, because it often, but not always, resultsin intact cells or colonies that maintain their flagellaand it allows for proper concentration of samples.Samples preserved with acidified Lugol’s fixative can be maintained for extended periods of time, althoughsamples, especially those in clear glass vials, mayrequire the addition of more preservative. Samplesfixed with formalin, formaldehyde, or glutaraldehydecan result in the loss of flagella and cell shape, andaggregation of the material over time will hinder concentration efforts (Takahashi, 1978; Wee, 1983;Graham et al., 1993). However, formaldehyde- andglutaraldehyde-based fixatives added to a sample justprior to observation can yield cells that maintain cellshape and internal structure. Other more specializedmethods for observing whole cells and siliceousremains were discussed in detail by Nicholls (1978)

and Wee (1983). Jensen’s stain (Jensen, 1962) has beenused successfully for observation of scales with LMwhen only bright field optics are available (Nicholls,1978). Wee (1983) reviewed the use of Nissenbaum’ssolution for fixation and simultaneous attachment ofcells to microscope slides, as well as the burnt-mountmethod for LM observation of siliceous remains.

Other projects may focus on quantifying theremains of synurophytes in sediment samples. Becausethe siliceous remains of synurophytes become archivedin the sediments, surface sediments can be used to estimate the abundances of all species that grew in agiven water body over the last few years. In addition,sediment cores can be used to study historical changesin synurophytes over time periods of tens to hundredsof years. Methods for the collection and preparation ofsediment samples for observation of synurophytes arewell established (Smol, 1995).

For studies that do not include quantification ofcells or for those that require critical identification oftaxa, plankton net tows are very useful. Whereas manysynurophytes are small, nets with a mesh size of 10 μmor less yield the best results. The net can be lowered tothe base of the photic zone and hauled vertically ordragged horizontally through the surface waters. Theadvantage of plankton net collections is that they canbe used directly to prepare samples for observationwith LM or electron microscopy (EM) that allow forobservation of many cells or their siliceous remains,thus greatly reducing the time needed to study a sample. Such concentrated samples aid finding andidentifying taxa, especially rare species, and thereforeprovide a useful complement to studies that requireconcentration of cells prior to enumeration. Althoughnet collections are not quantitative, the relative abun-dances of taxa are often maintained.

I often prepare net samples as soon after collectionas possible by pipeting aliquots of unfixed samplesonto both glass cover slips and aluminum foil, andimmediately drying them at room temperature or undervery low heat. This simple technique often results inintact cells. Collections that undergo large changes intemperature, are heated at a high temperature, or areallowed to sit for long periods of time prior to process-ing most often result in disarticulation of the silicascale coats. Standard critical point drying methods canbe used for work that requires observation of intactcells with scanning electron microscopy (SEM).

B. Preparing Samples for Observation with Light Microscopy

The most in-depth study of the preparation andobservation of synurophyte scales and bristles with LM

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was done by Wee (1983). Because the scales and bris-tles of synurophytes are siliceous in nature, methods to enhance contrast are needed to maximize the detailthat can be observed with LM and to make taxonomicdeterminations. Increased contrast is achieved througheither use of interference optics or use of different typesof mounting media, or both. Typically, phase contrastor differential interference contrast (DIC) methods areused to view siliceous remains in preparations thathave a mounting medium of high refractive index (RI)relative to silica. High magnification oil immersionobjective lenses with numerical apertures between 1.3and 1.4 yield the most information. I find that scalesare slightly less likely to be overlooked when phasecontrast optics is used. Because the majority of scalesare less than 5 μ m and because many of the details areclose to or below the limits of resolution with LM, it iscritical that the light path of the microscope be opti-mized, including the alignment of phase rings for phasecontrast, or the polarizer and analyzer for work withDIC.

Wee (1983) examined six different mounting mediafor use in observing synurophyte remains, including,Hyrax®, Naphrax, Pleurax, and air. The key to maxi-mizing the contrast is to imbed the remains in a medium with a refractive index that differs significantlyfrom that of silica (RI = ~1.5). The refractive indices ofHyrax®, Naphrax and Pleurax all range between 1.71and 1.75, and provide for excellent contrast of siliceousremains. However, presently, only Naphrax is commer-cially available. Mounts of scales and bristles in air (RI = 1.0) provide for the largest difference in RIbetween the specimen and mounting medium, andtherefore the maximum degree of contrast. Air mountscan be made easily by drying the siliceous remains froma sample onto a cover glass and mounting the coverglass onto a glass slide with a thin layer of nail polishalong the edges. The nail polish can be applied to eitherthe cover glass or the slide in several layers to provideenough thickness such that a layer of air exists betweenthem in the finished product. Normally, the initial layers of nail polish are allowed to dry and the coverglass is attached to the slide while the final layer of polish it is still sticky.

There are advantages and disadvantages to prepa-rations made using a solid mounting medium versus airmounts. Both preparations can be stored easily andarchived for long periods of time. Preparations usingsolid mounting media can be scribed with a diamondmarker and are less likely to be broken, especiallywhen immersion oil is being cleaned off the cover glass.Air mounts provide for the maximum amount of con-trast. Both types of preparations are relatively easy tomake, but air mounts do not require the purchase of

a mounting medium. As pointed out by Wee (1983),images of a silica specimen appear quite different whenobserved in a solid mounting medium of high RI versusair. The parts of each scale or bristle that have thethickest deposition of silica appear bright in a high RI medium and dark when mounted in air. Thus, structures such as thick ribs appear bright in the highRI medium and dark in air, whereas large pores appeardark and light, respectively.

Air mounts of samples can be viewed easily withan inverted microscope by directly using the cover-glasspreparation. The cover glass is positioned onto thestage with the sample side facing up toward the condenser. If the inverted microscope is outfitted withthe same objective lenses and condenser system (e.g.,one with a short working distance and a high numeri-cal aperature) as an upright microscope, an image ofsimilar quality to a standard upright microscope can beattained. This method has the obvious advantage thatthe cover glass need not be mounted onto a glass slideand, therefore, it can later be coated and viewed withSEM.

C. Preparing Samples for Observation with Electron Microscopy

A large number of species of synurophytes can bepositively identified only after observation with EM.For most routine identification work and to obtainquality micrographs, preparations for either scanningor transmission electron microscopy (TEM) can bemade easily and with little expense. In many cases analiquot from a sample concentrated with a planktonnet can be used directly to prepare SEM stubs andTEM grids.

For observation with SEM, samples simply can bedried onto a glass cover glass, a piece of aluminum foil, or directly onto an aluminum stub. The cover-glass or aluminum foil sample is attached to the aluminum stub using a nonconductive wax or double-sided tape, coated with gold, palladium, or a mixtureof both, and viewed directly. My personal preference is to use aluminum foil preparations rather than glasscover slips, because they greatly reduce the degree of charging, and the aluminum foil can be trimmed easily to fit multiple samples onto one stub. I have also found that if a field emission SEM is used to view samples, quality images can be attained withoutcoating the samples.

For observation with TEM, aliquots of samplescan be dried onto copper grids coated with Formvar orsome other material and coated with carbon to increasethe stability of the grids. Grids with a mesh size of 200suffice for most samples.

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D. Storage of Samples and Preparations of Scalesand Bristles

Glass microscope slide preparations of siliceousremains made with solid media or air mounts can bestored indefinitely. It is best to store such slides in aslotted box such that the slides remain in a horizontalposition with the sample side facing upward.Preparations made with a mounting medium that doesnot totally solidify at room temperature should beavoided for long-term storage of samples.

Aluminum SEM stubs also can serve as a long-termmethod for storing prepared samples. AlthoughFormvar grids, with or without a carbon coating, usedin TEM observation also can be used to store samples,they may break apart with time. In addition to glassslide and aluminum stub preparations, samples fromimportant collections can be dried onto cover glassesand aluminum foil, and stored in small Petri dishes.This method allows for future preparation of SEM orLM preparations using newly devised techniques ormounting media.

V. KEYS TO GENERA AND COMMON SPECIES FROMNORTH AMERICA

A. Introduction to Keys (Figs. 6–11)

The keys that follow can be used to identify generawithin the Synurophyceae, as well as the most commonspecies of Mallomonas and Synura found in NorthAmerica. The keys are based primarily on characteris-tics of body scales for Mallomonas and apical-spinedscales for Synura as observed with EM, but are alsodesigned to work for many, but not all, species usinghigh-resolution LM in conjunction with appropriatepreparations of scales. Electron microscopy is stressedbecause observation of many features is required toseparate species. Because of the ease of preparation andobservation of samples, and the high level of informa-tion that can be derived for both scales and cells, the

keys and associated micrographs are based on SEM.The reader is urged to make observations based onmany scales to more appropriately work through thekeys. In addition, the reader should consult the refer-ences listed in Section VI if a definitive identificationcannot been made and to gain more knowledge of eachspecies.

B. Key to Genera

Organisms are planktonic, unattached, unicellularor colonial in nature, motile, and golden brown incolor. Cells generally have two plastids aligned with thelong axis of the cell, lack an eye spot, and often possessa chrysolaminarin vesicle in the posterior of the cell.

C. Descriptions of Genera

Chrysodidymus Prowse (Figs. 2A and B and 6A)This genus comprises motile two-celled colonies

that swim in a more or less oscillating motion. The cells have an elongated vase-shaped structure that hasslightly wider posterior ends and two emergent flagella.The cells are attached by their posterior ends and faceoutward; their longitudinal axes become aligned at180°. Each cell is covered with siliceous spine-bearingscales that rsembles those of Synura sphagnicola. Thespines tend to be longer on scales positioned on theanterior end of the cell.

A rare but geographically widely known genusreported from a variety of lakes in Quebec (Puytorac et al., 1972), Ontario (Nicholls and Gerrath, 1985), theAdirondacks (Siver 1988a; Cumming et al., 1992a),Florida (Wujek and Bland, 1991), Michigan (Wujek andIgoe, 1989), Washington (Norris and Munch, 1970),southern New England (Siver and Hamer, 1992), andLouisiana (Wee et al., 1993). For ecological details, seeSections IIIA–F.

1a. Cells unicellular (Figs. 1A–C and 3A–E).......................................................................................................................... Mallomonas

1b. Cells in a colony.................................................................................................................................................................................2

2a. Colonies consist of only two basally attached cells that are linearly aligned and face 180° away from each other (Fig. 2A and B)....................................................................................................................................................................................Chrysodidymus

2b. Colonies of more than two, and usually many cells............................................................................................................................3

3a. Each cell of the colony individually surrounded by overlapping scales1. Colonies most often spherical, but may also be elongated.Commonly observed in North America (Figs. 1F–I and 3G and H)...........................................................................................Synura

3b. Multiple layers of scales surround the entire colony, not individual cells. To date, this organism has been reported only fromAustralia (Figs. 2C and 3F)..................................................................................................................................................Tessellaria

1S. lapponica is an exception (see text for details).

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542 Peter A. Siver

FIGURE 6 Scales of taxa associated with the Keys. A. Scales of Chrysodidymus synuroideus. B. Body scale of Mallomonas akrokomos. C. Domed and domeless scales of Mallomonas annulata. D. Body scale ofMallomonas asmundiae. E. Body scales of Mallomonas acaroides var. acaroides. F. Domed scale of Mallo-monas acaroides var. muskokana. G. Scales of Mallomonas canina. H. Scale of Mallomonas caudata. All scalebars = 2 μm.

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14. Synurophyte Algae 543

FIGURE 7 Scales of taxa associated with the Keys. A. Domed and domeless scales of Mallomonascorymbosa. Scale bar = 2 μm. B. Domed scale of Mallomonas crassisquama. Scale bar = 2 μm. C.Scales of Mallomonas cratis. Scale bar = 2 μm. Reprinted with permission from P. A. Siver, TheBiology of Mallomonas: Morphology, Taxonomy and Ecology. Copyright © 1991, Kluwer,Dordrecht. D. Body and collar scales of Mallomonas dickii. Scale bar = 2 μm. Reprinted with per-mission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy and Ecology.Copyright © 1991, Kluwer, Dordrecht. E. Body and spined scales of Mallomonas doignonii var.tenuicostis. Scale bar = 2 μm. F. Domed scale of Mallomonas duerrschmidtiae. Scale bar = 2 μm. G.Domed scales of Mallomonas elongata. Scale bar = 5 μm. Reprinted with permission from P. A. Siver,The Biology of Mallomonas: Morphology, Taxonomy and Ecology. Copyright © 1991, Kluwer,Dordrecht. H. A domed and domeless scale of Mallomonas galeiformis. Scale bar = 2 μm.

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544 Peter A. Siver

FIGURE 8 Scales of taxa associated with the Keys. A. Scale of Mallomonas hamata. Reprinted withpermission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy and Ecology. Copy-right © 1991, Kluwer, Dordrecht. B. Two scales of Mallomonas heterospina. C. Scale of Mallomonas hin-donii. Reprinted with permission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomyand Ecology. Copyright © 1991, Kluwer, Dordrecht. D. Body scale of Mallomonas lychenensis. E. Bodyscale of Mallomonas mangofera. F. Body and collar scales of Mallomonas mangofera var. foveata. G.Body scale of Mallomonas matvienkoae. H. Scale of Mallomonas papillosa. Reprinted with permissionfrom P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy and Ecology. Copyright © 1991,Kluwer, Dordrecht. All scale bars = 2 μm.

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14. Synurophyte Algae 545

FIGURE 9 Scales of taxa associated with the Keys. A. Domed scale of Mallomonas portae-ferreae var.portae-ferreae. Scale bar = 2 μm. Reprinted with permission from P. A. Siver and M. S. Vigna, NovaHedwigia 64:421–453. Copyright © 1997, Gebrüder Borntraeger, Stuttgart. B. Winged scale ofMallomonas pseudocoronata. Scale bar = 2 μm. C. Scales of Mallomonas pugio. Scale bar = 2 μm. D.Scale of Mallomonas punctifera. Scale bar = 1 μm. E. Scale of Mallomonas striata. Scale bar = 1 μm.Reprinted with permission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy andEcology. Copyright © 1991, Kluwer, Dordrecht. F. Domed scale of Mallomonas tonsurata. Scale bar =2 μm. G. Body scales of Mallomonas torquata. Scale bar = 2 μm. H. Body scales of Mallomonas torqua-ta forma simplex. Scale bar = 2 μm.

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546 Peter A. Siver

FIGURE 10 Scales of taxa associated with the Keys. A. Body scales of Mallomonas transsylvanica.Reprinted with permission from P. A. Siver, The Biology of Mallomonas: Morphology, Taxonomy andEcology. Copyright © 1991, Kluwer, Dordrecht. B. Spined scales of Synura curtispina. C. Caudal scalesof Synura curtispina. Reprinted with permission from P. A. Siver and M. S. Vigna, Nova Hedwigia64:421–453. Copyright © 1997, Gebrüder Borntraeger, Stuttgart. D. Spined scales of Synura echinulata.E. Posterior scale of Synura echinulata. F. Spined scales of Synura echinulata forma leptorrhabda.Reprinted with permission from P. A. Siver and M. S. Vigna, Nova Hedwigia 64:421–453. Copyright© 1997, Gebrüder Borntraeger, Stuttgart. G. Scale of Synura lapponica. H.Spined scale of Synura mollispina. All scale bars = 2 μm.

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FIGURE 11 Scales of taxa associated with the Keys. A. Scale of Synura petersenii. Scale bar = 2 μm. B. Spinedscale of Synura sphagnicola. Scale bar = 2 μm. C. Spined scales of Synura spinosa. Scale bar = 5 μm. D. Spineless scales of Synura spinosa. Scale bar = 5 μm. E. Spined scale of Synura uvella. Scale bar = 2 μm. F. Spineless scale of Synura uvella. Scale bar = 2 μm.

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Mallomonas Perty (Figs. 1A–E, 3A–E, and 4A–D)This genus comprises motile unicellular organisms

that range in size from 10 to 70 μm long and 5 to20 μm wide. Cells are spherical, ovid, or ellipse-shaped,golden in color, possess either a single or two apicallyemergent flagella, have one deeply lobed or two elon-gated chloroplasts, and have a posterior-positionedchrysolaminarin vacuole. Cells are covered with a highly organized layer of siliceous scales and bristles.Scales differ in morphology depending on their locationon the cell surface. Scales with spines are found only tothe posterior end of the cell. Bristles are thin, elongatedstructures that are tucked under the distal ends ofscales and radiate out from the cell. The arrangementof bristles on the cell surface varies between species,but they typically streamlined and oriented toward theposterior of the cell during active swimming.

A cosmopolitan genus that consists of many genera(see Sect. VD), they are planktonic and common in avariety of standing freshwaters across North Americaand worldwide (for ecological details, see Sects.IIIA–F).

Synura Ehrenberg (Figs. 1F–I, 3G and H, and 4E and F)A cosmopolitan genus that consists of spherical to

elongate-shaped motile colonies that swim in a tum-bling or rolling motion. Cells are most often pyriformor club-shaped and have wider anterior ends and slender more elongated posterior tails. The posteriorends of cells come in contact in the center of the colonyor, in the case of elongated forms, along a linear axis.

The number of cells per colony is highly variable,resulting in an equally variable colony diameter rang-ing from 30 to over 200 μm. Cells possess two unequaland apically emergent flagella, two golden-coloredchloroplasts positioned along the longitudinal axis ofthe cell, and are covered with a highly organized layerof overlapping siliceous scales (except for S lapponica).Spines are typically longer on the anteror ends of cellsthat face the outside of the colny.

Cosmopolitan and consisting of many genera (seeSect. VE), they are planktonic and common in a varietyof standing freshwaters across North America andworldwide (for ecological details, see Sects. IIIA–F).

Tessellaria Playfair (Figs. 2C and 3F)Tessellaria comprises a rare, spherical-shaped

motile colony that consists of from a few to severalhundred cells. Colonies range in diameter from 25 toabout 200 μm and swim in a rolling motion. Severallayers of radially symmetrical scales surround the entirecolony, not individual cells, and form in a light micro-scope what looks like a halo around the colony.Individual cells have two flagella, are golden in color,and are elongated; they have a wider anteror end and along thin cytoplasmic tail that attaches to a ringlikestructure in the center of the colony.

Rare; thus far reported (T. volvocina) only fromAustralia (Tyler et al., 1989; Pipes and Leedale, 1992;Lavau et al., 1997). Planktonic in freshwater, dystroph-ic, or slightly brackish standing waters, lagoons, andbillabongs (Tyler et al., 1989).

548 Peter A. Siver

D. Key to Common Species of Mallomonas

1a. Scales lack a V rib or with two lateral ribs that are not connected in the proximal region of the scale...............................................2

1b. Scales with a distinct V rib or a continuous submarginal rib that is uninterrupted in the distal region...............................................8

2a. Body scales with a dome....................................................................................................................................................................3

2b. Body scales lack a dome ....................................................................................................................................................................5

3a. Scales ovate with a shallow dome positioned to one side of the distal end; lack distinct secondary structures, including submarginalribs; base plate pores are larger in the proximal region, becoming smaller and less distinct or lacking on the distal end. With LM theproximal portion of the scale along the rim appears more transparent and the dome can be observed (Fig. 8A).................M. hamata

3b. Scales are quadrate in shape with a rounded proximal end and a somewhat squared distal end with a more or less centrally posi-tioned dome. Scales with two, roughly parallel, submarginal ribs that originate at the base of the dome and terminate, but do notconnect, in the proximal region of the scale; submarginal ribs clearly seen with LM; shield with additional secondary ornamenta-tion....................................................................................................................................................................................................4

4a. Distal two-thirds of the shield with a well developed reticulum of ribs forming large pores; reticulum easily observed with LM(Fig. 9D).........................................................................................................................................................................M. punctifera

4b. Distal two-thirds of shield ornamented with closely spaced, and more or less parallel transverse ribs; ribbing on shield observedwith EM, but not LM (Fig. 10A)..............................................................................................................................M. transsylvanica

5a. Scales thick, large, heavily silicified, with two rows of large pits or pores aligned parallel to the long axis of the scale and clearlyobserved with LM; shield surface with prominent, closely spaced papillae not observed with LM (Fig. 14.8D)............M. lychenensis

5b. Scales lack the two rows of large prominent pits................................................................................................................................6

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6a. Scales small (1.7–3.8 μm × 0.6–2.0 μm), with a rounded U-shaped proximal end and a pointed inverted V-shaped distal end; possessa distinctive patch of base plate pores in the proximal half of the scale and a serrated distal margin. The patch of pores is moreclearly observed from the underside with SEM and will appear as a more transparent zone with LM (Fig. 6B)............M. akrokomos

6b. Scales much larger, usually larger than 4 μm, and typically up to 6 μm in length; distal and proximal ends more or less rounded, U-shaped, not pointed; lack distinctive patch of pores.......................................................................................................................7

7a. Scales oval to elliptical, symmetrical, with a secondary layer consisting mostly of small pores covering the distal one-half to two-thirds of the scale. In LM the distal portion of the scale appears opaque due to the secondary thickening (Fig. 8G)...................................................................................................................................................................................M. matvienkoae

7b. Scales more rounded, but often slightly asymmetrical; lack a secondary layer or any secondary structures; appear unornamented inboth EM and LM (Fig. 6H)................................................................................................................................................M. caudata

8a. All body scales lack domes; V rib lies close to the rim; arms of the V rib are connected to thick well developed anterior submarginalribs such as to form a rhomboidal or diamond shape. Bristles restricted to anterior collar scales; posterior scales often have longspines. (organisms within the section Torquatae2)..............................................................................................................................9

8b. At least some, if not all, body scales possess domes. Scales not rhomboidal in shape and cells not as described above.....................13

9a. Surface of scales covered with closely spaced papillae (Fig. 8E and F)............................................................................M. mangofera

9b. Surface of scales with little or no secondary structure, or consisting of a series of ribs, not papillae.................................................10

10a. Ribs on the scale consist of a series of very short struts radiating from the submarginal rib a short distance onto the shield; other-wise the shield is devoid of secondary structure (Fig. 9H).................................................................................M. torquata f. simplex

10b. Ribs extend across entire area of the shield......................................................................................................................................11

11a. Ribs form a reticulum on the shield (Fig. 19G)................................................................................................M. torquata f. torquata

11b. Ribs are closely spaced, more or less parallel, and each rib traverses the shield................................................................................12

12a. Scales very small with a mean length of only 2.3 μm; cells also small with a mean length of only 11 μm (Fig. 17D)..............M. dickii

12b. Scales and cells significantly larger, with mean values of 3.8 and 27 μ m, respectively (Fig. 7E)............M. doignonii (several varieties)

13a. Base of the V rib very broad, U-shaped with forward- projecting arms that encircle and fuse at the distal-most edge of the scale,forming a continuous submarginal rib. A number of prominent, thick ribs on the shield, including a single large rib—the transverserib, that transects the shield perpendicular to the longitudinal axis of the cell..................................................................................14

13b. Base of the V rib not broadly U-shaped; the arms of the V rib or anterior submarginal ribs do not completely encircle and fuse infront of the dome; scales lack a single large rib transversing the shield.............................................................................................17

14a. Body scales widest near the distal end with a very broad dome that has from five to eight evenly spaced parallel ribs (Fig. 9C)..............................................................................................................................................................................................M. pugio

14b. Domes of body scales smaller and lack a series of parallel ribs.........................................................................................................15

15a. A relatively large number of ribs originate from each side of the transverse rib and radiate onto the shield, each, in turn, dividing orspliting to form a dense reticulum of ribs on the shield; some scales may have ribs on the dome, but they are not aligned in a paral-lel fashion (Fig. 8B).......................................................................................................................................................M. heterospina

15b. Scales with a single large rib radiating from the center of the transverse rib and terminating near the base of the dome. A similar ribradiates from the transverse rib toward the proximal end of the scale and commonly divides once or twice. The result is that thearea of the shield proximal to the transverse rib is divided more than the distal portion of the shield..............................................16

16a. Areas of the shield between the ribs ornamented with papillae. Needle bristles lack subapical tooth (Fig. 6G).....................M. canina

16b. Shield lacks papillae. Needle bristles with subapical tooth (Fig. 8C)....................................................................................M. hindonii

17a. Secondary structures lacking on the shield and flanges; scales large with well developed V ribs and anterior submarginal ribs. Thearms of the V rib bend and become continuous with the anterior submarginal ribs (Fig. 7G)............................................M. elongata

17b. Scales more complex in nature; possess secondary structures on the shield and/or a rim..................................................................18

18a. Shields with papillae.........................................................................................................................................................................19

18b. Shields lacking papillae....................................................................................................................................................................20

19a. All scales with small domes and a series of three to eight evenly spaced parallel ribs on each anterior flange. Papillae cover the shieldand often the dome, but are lacking on the flanges (Fig. 8H)............................................................................................M. papillosa

19b. Each cell has body scales with and without domes. Papillae cover the shield, the dome, and the anterior flanges; the latter lackingparallel ribs. Except for base plate pores, the posterior flange is unornamented (Fig. 6C).................................................M. annulata

14. Synurophyte Algae 549

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20a. Secondary layer on the shield consists of parallel transverse ribs......................................................................................................21

20b. Secondary layer on the shield essentially lacking, or consists of a network of circular holes or pores, or an irregular reticulation ofribs...................................................................................................................................................................................................25

21a. Transverse ribs arranged in a parallel fashion and connected by numerous ribs that run perpendicular to the transverse ribs; flangeareas lack ribs, but the posterior flange may be covered with a reticulation of pores; scales large, mostly between 4 and 7.5 μm;dome and domeless scales present; domes are large and prominent (Fig. 9A)...............................M. portae-ferreae var. portae-ferreae

21b. Transverse ribs on the shield are prominent, arranged in a parallel fashion, and may be connected by much smaller and less promi-nent ribs. Flange areas and domes may also possess parallel ribs............................... .....................................................................22

22a. Posterior and anterior flanges lack prominent ribs. The distal-most transverse ribs on the shield, especially on domed scales, areoften larger and more prominent; the apical-most domed scales have one or a few transverse shield ribs (Fig. 7H)......................................................................................................................................................................................M. galeiformis

22b. Posterior flange with prominent ribs................................................................................................................................................23

23a. The posterior flange has a few widely and irregularly spaced ribs. The arms of the V rib extend to the margin of the scale and donot bend, and become continuous with the anterior submarginal ribs. Ribs on the anterior flange prominent, arranged parallel, andgenerally spaced equally with those on the shield (Fig. 9E)...................................................................................................M. striata

23b. The posterior flange has many evenly spaced ribs. The arms of the V rib extend to the scale margin or bend and are continuouswith the anterior submarginal ribs. The anterior flange either lacks ribs or has ribs that are continuous with those on theshield................................................................................................................................................................................................24

24a. Ribs on the posterior flange spaced slightly wider than those on the shield. The anterior submarginal ribs are lacking or at bestpoorly developed; ribs on the shield are continuous onto the anterior flanges; dome with strongly U-shaped ribs (Fig. 7C)...M. cratis

24b. Ribs on the posterior flange are usually spaced similarly to those on the shield. The arms of the V rib bend and become continuouswith the anterior submarginal ribs; ribs are often lacking on the anterior flange; ribs on the dome are spaced similarly to those onthe shield and aligned parallel or at a slight angle with the longitudinal axis of the cell (Fig. 6D)..................................M. asmundiae

25a. Secondary layer on the shield is composed of small to medium-sized pores, close in diameter to those of the base plate; there is awell developed window at the base of the V rib; posterior flange may also contain a secondary layer of pores, but is not traversedwith parallel ribs..............................................................................................................................................................................26

25b. Secondary layer on the shield is lacking or composed of a reticulation of ribs or large pores; posterior flange is crossed or traversedwith a series of parallel ribs.............................................................................................................................................................27

26a. Scales are small, most range between 2.7 and 4.4 μm in length; both domed and domeless scales present; on domed scales the armsof the V rib extend to or close to the dome, resulting in anterior submarginal ribs that are very short or lacking altogether (Fig. 9F)........................................................................................................................................................................................M. tonsurata

26b. Scales often much larger, most ranging in length from 4.2 to 5.2 μm; scales with distinct anterior submarginal ribs (Fig. 7A)......................................................................................................................................................................................M. corymbosa

27a. Secondary layer on the shield is largely lacking (Fig. 6F)........................................................................M. acaroides var. muskokana

27b. Secondary layer on the shield consists of large pores or a reticulation of ribs...................................................................................28

28a. Secondary layer on the shield consists of somewhat wavy ribs, most of which originate from the V rib and extend onto the shield.The arms of the V rib extend to the margin of the scale and do not bend, and become continuous with the anterior submarginal ribs(Fig. 6E).....................................................................................................................................................M. acaroides var. acaroides

28b. Secondary layer on the shield generally well developed and consisting of a series of large (relative to the base plate pores)pores................................................................................................................................................................................................29

29a. Scales are very large, commonly between 6.4 and 14.1 μm in length, and possess a large, forward-projecting wing (Fig. 9B)..............................................................................................................................................................................M. pseudocoronata

29b. Scales may be large, but lack a forward-projecting wing..................................................................................................................30

30a. Domed scales are large, ranging in length from 4.7 to 8.6 μm, with relatively small domes; domes usually marked with parallel ribs;arms of the V rib bend and become continuous with the anterior submarginal ribs (Fig. 7F).................................M. duerrschmidtiae

30b. Scales usually smaller, ranging in length from 3.8 to 6.7 μm, with relatively large domes often marked with papillae; arms of V ribextend to the margin of the scale and are not continuous with the anterior submarginal ribs (Fig. 7B)......................M. crassisquama

2Only a few of the many taxa described in the section Torquatae are included in the key. Some of the taxa are difficult to positively identify andthe reader is urged to consult the references listed in Table I for more details.

550 Peter A. Siver

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VI. GUIDE TO LITERATURE FOR SPECIES IDENTIFICATION

The monographs by Asmund and Kristiansen(1986) and Siver (1991a) provide excellent general references for Mallomonas (Table I). The work byAsmund and Kristiansen (1986) is largely based onTEM images and provides well-written descriptions aswell as previous records for all Mallomonas taxadescribed at the time of publication. Siver (1991a) pro-vides many SEM micrographs of whole cells, scales andbristles, morphological analyses, and summaries of eco-logical preferences for many species of Mallomonas.

Nicholls and Gerrath (1985) and Siver (1987) are twoof the more useful publications for identifying speciesof Synura in North American waters, and together pro-vide TEM and SEM images of most of the commonspecies. Wujek and Wee (1983) and Graham et al.(1993), and Tyler et al. (1989) provide information onChrysodidymus and Tessellaria, respectively.

Three other references are especially valuable foridentification of synurophytes as well as other scaledchrysophytes. Although the work of Takahashi (1978)is based largely on water bodies in Japan, it providesmuch useful information and TEM images of manyspecies commonly found in North America. Wee

14. Synurophyte Algae 551

E. Key to Common Species of Synura

1a. Scales biradially symmetrical with a central papillae (Fig. 10G)........................................................................................S. lapponica

1b. Scales bilaterally symmetrical and lack a central papillae...................................................................................................................2

2a. Anterior scales have a keel, a raised hollow cylinder centrally positioned on the base plate; usually with well developed ribs or strutsthat run perpendicular from the keel to the scale border (Fig. 11A)3...................................section Peterseniae including, S. petersenii

2b. Anterior scales lack a keel but possess a distally attached and forward-projecting spine.....................................................................3

3a. Scales with evenly spaced ribs under the rim; spine scales with a short, stout, conical spine with multiple teeth at the distal tip. Ribsbeneath the rim are more easily observed with LM or TEM (Fig. 11E and F).........................................................................S. uvella

3b. Scales lack ribs under the rim; spines not short, stout and conical in shape........................................................................................4

4a. Base plate consists of rather large, evenly spaced perforations; lack additional secondary structures; rim encircles at least four-fifthsof the perimeter on spined scales and the entire perimeter on spineless scales (Fig. 11B)................................................S. sphagnicola

4b. Proximal portion of anterior scale with perforations as above, but the distal portion with secondary siliceous features.....................5

5a. Tip of spine a sharp acute point; distal portion of scale with a raised thickened region beneath that lies as either a series of vermi-form ribs or a series of closely spaced and linearly arranged papillae (seen only with EM); a series of short ribs run perpendicular tothe distal margin; posterior scales elongated, often with a very short spine, and with a more extensive thickened region than foundon anterior scales...............................................................................................................................................................................6

5b. Tip of spine blunt and may possess teeth; secondary ribs form a honeycomb reticulation on at least the distal portion of the scale; athin siliceous membrane may cover at least part of the secondary honeycomb; a series of short ribs run perpendicular to the distalmargin; posterior scales lack spines....................................................................................................................................................8

6a. Distal end of scale composed of closely spaced papillae arranged in linear fashion (observed best with TEM)..............S. mammillosa

6b. Distal end of scale composed of vermiform ribs, not papillae.............................................................................................................7

7a. Series of vermiform ribs rather extensive, covering one-third to one-half of the surface area on anterior scales, and often reachestwo-thirds of the surface area on the posterior scales; anterior scales commonly 2 to 3.5 μm long (Fig. 10D and E).........................................................................................................................................................................................S. echinulata

7b. Vermiform ribbing reduced to a small narrow region; pores on the shield rather large; scales are small, usually around 2 μ m long(Fig. 10F).................................................................................................................................................S. echinulata f. leptorrhabda

8a. Honeycomb reticulum covers most, if not all, of the scale; a thin membrane may cover ca. two-thirds to three-quarters of the hon-eycomb layer; posterior scales rectangular or long, narrow, and somewhat triangular, with an elongated distal end (Fig. 10H).........................................................................................................................................................................................S. mollispina

8b. Honeycomb reticulum covers the distal ca. one-third of the scale; a thin membrane may cover the honeycomb reticulum.................9

9a. Spines generally small, ~0.5–2.0 μm long; posterior-most scales elongated, slipper-shaped, generally lack secondary structure, andare encircled by a thick rim that imparts a diamond shape to the scale (Fig. 10B and C)..................................................S. curtispina

9b. Spines longer, ~2.8–3.5 μ m long; posterior scales teardrop-shaped, lack ribbing on the shield, and completely encircled with a rimthat does not form a diamond pattern (Fig. 11C and D).......................................................................................................S. spinosa

3Scales of S. australiensis have a morphology similar to those of S. petersenii, but are much longer, often over 8 μm in length.

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(1982) is one of the few in-depth studies of primarilyalkaline habitats from the midwestern United States,and also provides many LM images of whole cells andscales, and a taxonomic key. Cronberg (1989) providesa review of taxa found in tropical localities. Referencesof studies of synurophytes and scaled chrysophytesfrom specific regions of North American are listed inTable I.

ACKNOWLEDGMENTS

The writing of this chapter was funded, in part, bygrants from the National Science Foundation (DEB-9306587 and DEB-9615062). I would like to thankAnne Lott for help in assembling the references, andKen Nicholls and Jim Wee for helpful comments.

LITERATURE CITED

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Beech, P. L. 1990b. Direct observations on flagellar transformation in

552 Peter A. Siver

TABLE I A List of Useful Publications for the Identification of Species and Subspecific Taxa of Synurophyceaeand Other Scaled-Chrysophytes with an Emphasis on References from North American Localities

Reference Region Comments

Asmund and Hilliard (1961) Alaska Work on MallomonasAmund and Takahashi (1969) Alaska Work on MallomonasAsmund and Kristiansen (1986) Monograph thesis on MallomonasCronberg (1989) Tropics Review of work from tropical localitiesGretz et al. (1979, 1983) Arizona TEMKling and Kristiansen (1983) Canada Central and northern areasKristiansen (1975) Western Canada Collections from Alberta and British ColumbiaKristiansen (1992) Greenland Arctic sitesMcKenzie and Kling (1989) Northwest territories Arctic regon, Mackenzie DeltaNicholls (1982) Ontario Work on MallomonasNicholls (1988a) Ontario Provides checklist of Mallomonas from NANicholls and Gerrath (1985) Ontario Work on Synura; discusses taste and odorPetersen and Hansen (1956, 1958) General Works on SynuraSiver (1987) Connecticut Work on Synura; SEMSiver (1988b) Adirondacks, New York Soft-water localitiesSiver (1991a) Mostly Connecticut Monograph on MallomonasSiver and Wujek (1993) Florida Eutrophic collections; SEM; subtropicsSiver and Wujek (1998) Florida Ocala National Forest; acidic habitats; subtropicsTakahashi (1978) Japan Thesis on scaled chrysophytesTyler et al. (1989) Australia Work on TessellariaWawrzyniak and Andersen (1985) Northern Boreal Soft-water sites; scaled chrysophytesWee (1982) Iowa Thesis on scaled chrysophytes; alkaline sitesWee et al. (1993) Louisiana Sothern Atlantic Coastal Plain; subtropicsWujek (1984) Florda Scaled chrysophytes; TEMWujek and Hamilton (1972, 1973) Michigan Scaled chrysophytes; TEMWujek et al. (1975, 1977) Michigan Scaled chrysophytes; TEMWujek and Wee (1983) General Work on ChrysodidymusWujek and Weis (1984) Kansas Scaled chrysophytes; TEM

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Mallomonas splendens (Synurophyceae). Journal of Phycology26:90–95.

Beech, P. L., Wetherbee, R., Pickett-Heaps, J. D. 1990. Secretion anddeployment of bristles in Mallomonas splendens (Synuro-phyceae). Journal of Phycology 26:112–122.

Belcher, J. H. 1969. Some remarks upon Mallomonas papillosaHarris and Bradley and M. caleolus Bradley. Nova Hedwigia18:257–270.

Bourrelly, P. 1981. Les algues d’eau douce. II. Les algues jaunes etbrunes. Societe Nouvelle des Editions Boubee, Paris.

Brugerolle, G., Bricheux, G. 1984. Actin microfilaments are involvedin scale formation of the chrysomonad cell Synura. Protoplasma123:203–212.

Calado, A. J., Rino, J. A. 1994. Chlorodesmos hispidus, a morpho-logical expression of Synura spinosa (Synurophyceae). NordicJournal of Botany 14:235–239.

Cavalier–Smith, T. 1986. The kingdon Chromista: Origin and sys-tematics. Progress in Phycological Research 4:309–347.

Charles, D. F., Smol, J. P. l988. New methods for using diatoms andchrysophytes to infer past pH of low-alkalinity lakes.Limnology and Oceanography 33:1451–162.

Clasen, J., Bernhardt, H. 1982. A bloom of the ChrysophyceaeSynura uvella in the Wahnbach reservoir as indicator for the release of phosphates from the sediment. Archiv fürHydrobiologie Beiheft 1861–86.

Cronberg, G. 1980. Cyst development in different species ofMallomonas (Chrysophyceae) studied by scanning electronmicroscopy. Archiv für Hydrobiologica Scandinavica56:421–434.

Cronberg, G. 1982. Phytoplankton changes in Lake Trummeninduced by restoration. Folia Limnologica Scandinavica18:11–119.

Cronberg, G. 1986. Chrysophycean cysts and scales in lake sediments: A review, in: Kristiansen, J., Andersen, R. A., Eds.,Chrysophytes: Aspects and problems. Cambridge UniversityPress, pp 281–315.

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