PHYLOGENETIC POSITION OF CHAETOSPHAERIDIUM (CHLOROPHYTA), A BASAL LINEAGE IN THE CHAROPHYCEAE INFERRED FROM 18S rDNA SEQUENCES

We sequenced the nuclear-encoded small-subunit ribosomal RNA gene (18S rDNA) of Chaetosphaeridium globosum (Nordst.) Klebahn, a microscopic freshwater epiphytic chlorophyte, to assess its phylogenetic affinities in the Chlorophyta. A phylogenetic analysis of a broad sampling of green algal taxa and Chaetosphaeridium confirmed that this alga is a member of the Charophyceae (Streptophyta) as earlier microscopical studies had suggested. However, more detailed phylogenetic analyses of the streptophyte lineage showed that contrary to expectations based on the ultrastructure of the zoospores, the presence of a unique type of setae, the oogamous mode of reproduction, and the occurrence of oscillatory rotations of the cytoplasm, Chaetosphaeridium and Coleochaete are not closely related and do not form a monophyletic clade. Instead, Chaetosphaeridium represents an early branch in the streptophyte lineage that had a near-simultaneous origin as the Charalean clade and a clade formed by all remaining streptophytes examined ( Klebsormidium, Coleochaete, Chlorokybus, Zygnematales, and bryophytes). All phylogenetic inference methods used (neighbor-joining analysis of Kimura distances, maximum likelihood, and maximum parsimony) resulted in essentially the same tree topology. No Group I introns were found in the 18S rDNA coding region of Chaetosphaeridium. Our molecular phylogenetic analysis of Chaetosphaeridium supports a recent cladistic classification of the Streptobionta by Kenrick and Crane in which Chaetosphaeridium is placed in a monotypic division and class, Chaetosphaeridiophyta and Chaetosphaeridiophyceae, respectively.     

PHYLOGENETIC POSITION OF KOLIELLA (CHLOROPHYTA) AS INFERRED FROM NUCLEAR AND CHLOROPLAST SMALL SUBUNIT rDNA

The phylogenetic position of Koliella , a chlorophyte characterized by Klebsormidium type cell division, was inferred from analyses of partial 18S rDNA and partial 16S rDNA. Parsimony and distance analyses of separate and combined data sets indicated that the members of Koliella belonged to Trebouxiophyceae, and high decay indices and bootstrap values supported this affinity. However, the genus appeared to be polyphyletic. Koliella spiculiformis , the nomenclatural type of the genus, was allied with Nannochloris eucaryota and the "true" chlorellas ( Chlorella vulgaris , C. lobophora , C. sorokiniana , and C. kessleri ). The close relatives of Koliella longiseta (≡ Raphidonema longiseta ) and Koliella sempervirens appeared to be Stichococcus bacillaris and some species traditionally classified in Chlorella that were characterized by the production of secondary carotenoids under nitrogen-deficient conditions. This clade was also supported by the presence of a relatively phylogenetically stable group I intron (1506) in the 18S rRNA gene. Because of the presence of Klebsormidium type cell division, some authors regarded the members of Koliella as closely related to charophytes. Molecular analyses, however, did not confirm this affinity and suggested that a Klebsormidium type cell division is homoplastic in green plants.     

DIVERSITY AND PHYLOGENETIC PLACEMENT OF BRACTEACOCCUS TEREG (CHLOROPHYCEAE,CHLOROPHYTA) BASED ON 18S RIBOSOMAL RNA GENE SEQUENCE DATA1

Sequence data from the nuclear small-subunit ribosomal RNA gene was obtained for nine strains of Bracteacoccus Tereg, representing at least five morphological species and four distinct geographic locations. These, along with sequence data from two additional chlorophycean taxa, Spongiochloris spongiosa Starr and Ascochloris multinucleata Bold et MacEntee, and 48 published sequences from green algal taxa, were used to determine the phylogenetic placement of Bracteacoccus with respect to other chlorophycean green algae. Results support the monophyly of Bracteacoccus strains, contrasting with patterns observed so far for many other coccoid green algae. The range of variation among Bracteacoccus strains is similar to that of other congeners. Basal body orientation in Bracteacoccus has been interpreted as clockwise; however, the 18S data point to a relationship between Bracteacoccus and taxa with the directly opposed configuration of the flagellar apparatus. No close relationship was found to the multinucleated green coccoids with clockwise orientation of basal bodies, such as Spongiochloris, or to those with parallel basal bodies, such as Spermatozopsis. However, 18S data confirm that the motile and vegetative cells of Bracteacoccus are structurally distinct from the representatives of sphaeroplealean families currently studied. It is premature to reclassify Bracteacoccus until 18S comparisons can be made with additional sphaeroplealean taxa and with algae with similar flagellar structure such as Dictyochloris and Heterochlamydomonas.     

A PHYLOGENETIC ANALYSIS OF THE SYNUROPHYCEAE USING MOLECULAR DATA AND SCALE CASE MORPHOLOGY

The phylogeny of the Synurophyceae was investigated by parsimony analysis of scale case characters and small-sub unit (18S) ribosomal RNA (rRNA) sequence data. Analysis of 1 eustigmatophycean (outgroup), 3 chrysophycean, and 10 synurophycean 18S rRNA sequences corroborated the inference from ultrastructural information that the Synurophyceae is a monophyletic assemblage . Tessellaria vol-vocina, which had been tentatively proposed as a member of the Synurophyceae, was confirmed as the earliest lineage within the Synurophyceae by both the molecular analysis and an evaluation of published ultrastructural data. A second set of analyses investigated the relationships among Tessellaria volvocina, 6 Synura species, and 10 Mallomonas species/varieties, with particular reference to the validity of current classifications of the Synurophyceae and the characters upon which they are based. The molecular and scale case phylogenies were not totally resolved but were largely congruent. The data sets were combined to produce another phylogeny, which showed greater resolution. The combined phylogeny weakly supported our representatives of Synura and Mallomonas as monophyletic groupings and also upheld several of the sections within these genera that are recognized by current classifications. However, some changes to the classification and delineation of these genera are recommended and predicted. Both our 18S rRNA sequence and scale case data sets were more appropriate for examining the branching order among the more closely related text rather than resolving the deeper branching points of the synurophycean phylogeny .     

PHYLOGENETIC RELATIONSHIPS AMONG ISOLATES OF EUDORINA SPECIES (VOLVOCALES, CHLOROPHYTA) INFERRED FROM MOLECULAR AND BIOCHEMICAL DATA

Phylogenetic analyses of 19 strains representing five species of Eudorina, one strain of Pleodorina indica, and seven strains of Yamagishiella unicocca were carried out by sequencing the internal transcribed spacer region (ITS 1 and ITS 2) of the nuclear ribosomal DNA (rDNA) repeats. The sequence data resolved five phylogenetic groups, one consisting of Y. unicocca and the other four encompassing all the Eudorina species. Two isolates, Eudorina sp. (ASW 05157) and Pleodorina indica (ASW 05153), were of uncertain affiliation. Whereas one monophyletic group included strains of E. elegans only, the other strains of E. elegans appeared alongside E. cylindrica, E. illinoisensis, and E. unicocca var. unicocca in the other Eudorina clades. The distribution pattern of the carotenoid loroxanthin ([3R,3'R,6'R]-β,ε-carotene-3,19,3'-triol), a systematically useful biochemical marker within chlorophycean flagellates, was shown to match the evaluated molecular data. Whereas it was either totally absent or universally present in six of the deduced phylogenetic lines, it occurred randomly in the E. elegans clade containing only E. elegans isolates. The results substantiated the current hypothesis that the unique vegetative morphology of E. elegans has independently arisen at various times during evolution and that it is not a marker of a monophyletic group.     

CHARACTERIZATION AND PHYLOGENETIC POSITION OF THE ENIGMATIC GOLDEN ALGA PHAEOTHAMNION CONFERVICOLA: ULTRASTRUCTURE, PIGMENT COMPOSITION AND PARTIAL SSU rDNA SEQUENCE

The morphology, ultrastructure, photosynthetic pigments, and nuclear-encoded small subunit ribosomal DNA (SSU rDNA) were examined for Phaeothamnion confervicola Lagerheim strain SAG119.79. The morphology of the vegetative filaments, as viewed under light microscopy, was indistinguishable from the isotype. Light microscopy, including epifluorescence microscopy, also revealed the presence of one to three chloroplasts in both vegetative cells and zoospores. Vegetative filaments occasionally transformed to a palmelloid stage in old cultures. An eyespot was not visible in zoospores when examined with light microscopy, but small droplets, similar to eyespot droplets, were apparent beneath the shorter flagellum when cells were viewed with electron microscopy. Zoospores had two flagella that were laterally inserted in the cell approximately one-third of the cell length from the apex. The longer flagellum was directed anteriorly and the shorter flagellum was directed posteriorly. Electron microscopy revealed the presence of tubular tripartite flagellar hairs on the longer flagellum, but no lateral filaments were found on the tripartite hairs. The general organization of the flagellar root system was similar to that of zoospores belonging to the Xanthophyceae and Phaeophyceae. However, the transitional region of the flagella contained a transitional helix with four to six gyres. Microtubular root R₁ consisted of six microtubules at its proximal end and one microtubule at its distal end. Roots R₂ and R₄ consisted of one microtubule each and root R₃ consisted of two microtubules. No rhizoplast was found. Thin-layer chromatography revealed the presence of fucoxanthin, diadinoxanthin, neoxanthin, and heteroxanthin as well as chlorophylls a, c₁ and c₂. High-performance liquid chromatography revealed the presence of fucoxanthin, diadinoxanthin, diatoxanthin, heteroxanthin, and β,β-carotene as well as chlorophylls a and c. The complete sequence of the SSU rDNA could not be obtained, but a partial sequence (1201 bases) was determined. Parsimony and neighbor-joining distance analyses of SSU rDNA from Phaeothamnion and 36 other chromophyte algae (with two Öomycete fungi as the outgroup) indicated that Phaeothamnion was a weakly supported (bootstrap = <50%, 52%) sister taxon to the Xanthophyceae representatives and that this combined clade was in turn a weakly supported (bootstrap = <50%, 67%) sister to the Phaeophyceae. Based upon ultrastructural observations, pigment analysis, and SSU rDNA phylogenetic analysis, Phaeothamnion is not a member of the Chrysophyceae and should be classified as incertae sedis with affinities to the Xanthophyceae and Phaeophyceae.     

PHYLOGENETIC POSITION OF BOLBOCOLEON PILIFERUM (ULVOPHYCEAE,CHLOROPHYTA): EVIDENCE FROM REPRODUCTION,ZOOSPORE AND GAMETE ULTRASTRUCTURE,AND SMALL SUBUNIT RRNA GENE SEQUENCES1

Aspects of the reproduction of Bolbocoleon piliferum N. Pringsheim, a common, small, filamentous, endophytic marine green alga, were examined by LM and TEM. These observations were combined with phylogenetic analysis of nuclear‐encoded small subunit rRNA gene sequences to assess the phylogenetic position of B. piliferum. Quadriflagellate zoospores and planozygotes derived from fusion of isogametes yielded plants with identical morphology. Zoosporangia and gametangia divided by sequential cleavages. Plugs at the apices of zoosporangia and gametangia formed during development; tubes were found at zoosporangial and gametangial apices after swarmer release. Flagellar apparatuses of zoospores and gametes were similar to those of algae in the Ulvales (Ulvophyceae), except that terminal caps were entire rather than bilobed and rhizoplasts and “stacked” microtubular root configurations were absent. Structures associated with planozygotes were identical to those observed in other algae currently assigned to Ulotrichales and Ulvales. Molecular phylogenetic analyses placed B. piliferum within the Ulvophyceae, at the base of a clade that contains representatives of the families Ulvaceae, Ulvellaceae, and Kornmanniaceae. The results support an earlier hypothesis that B. piliferum constitutes a distinct lineage. Analyses including Kornmanniaceae recover monophyletic Ulotrichales and Ulvales, whereas analyses omitting the Kornmanniaceae indicate that Ulotrichales is paraphyletic. The structures associated with gamete fusion are conserved within Ulotrichales and Ulvales and perhaps more widely within Chlorophyta.     

ANALYSIS OF A PLASTID MULTIGENE DATA SET AND THE PHYLOGENETIC POSITION OF THE MARINE MACROALGA CAULERPA FILIFORMIS (CHLOROPHYTA)1

Molecular phylogenetic relationships within the Chlorophyta have relied heavily on rRNA data. These data have revolutionized our insight in green algal evolution, yet some class relationships have never been well resolved. A commonly used class within the Chlorophyta is the Ulvophyceae, although there is not much support for its monophyly. The relationships among the Ulvophyceae, Trebouxiophyceae, and Chlorophyceae are also contentious. In recent years, chloroplast genome data have shown their utility in resolving relationships between the main green algal clades, but such studies have never included marine macroalgae. We provide partial chloroplast genome data (～30,000 bp, 23 genes) of the ulvophycean macroalga Caulerpa filiformis (Suhr) K. Herig. We show gene order conservation for some gene combinations and rearrangements in other regions compared to closely related taxa. Our data also revealed a pseudogene (ycf62) in Caulerpa species. Our phylogenetic results, based on analyses of a 23‐gene alignment, suggest that neither Ulvophyceae nor Trebouxiophyceae are monophyletic, with Caulerpa being more closely related to the trebouxiophyte Chlorella than to Oltmannsiellopsis and Pseudendoclonium.     

CONCORDANCE OF MOLECULAR AND ULTRASTRUCTURAL DATA IN THE STUDY OF ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE1

Alternative evolutionary hypotheses generated from features of vegetative cell morphology and motile cell ultra-structure were investigated using a molecular data set. Complete nuclear-encoded small subunit (18S) ribosomal RNA (rRNA) gene sequences were determined for six species (three each) of the chlorococcalean green algae “Neo chloris” and Characium. Based on motile cell ultra-structure, it was previously shown that both genera could be separated into three distinct groups possibly representing three separate orders and two classes of green algae. 18S rRNA gene sequences were also obtained for three additional taxa, Dunaliella parva Lerche, Pediastrum duplex Meyen, and Friedmannia israelensis Chantanachat and Bold. These organisms were selected because each, in turn, is a representative of one of the three ultrastructural groups into which the Neochloris and Characium species are separable. Phylogenetic analyses utilizing the molecular data fully support the ultrastructural findings, suggesting that the similar vegetative cell morphologies observed in these organisms have resulted from convergence.     

ASSESSING THE RELATIONSHIPS OF SOME COCCOID GREEN LICHEN ALGAE AND THE MICROTHAMNIALES (CHLOROPHYTA) WITH 18S RIBOSOMAL RNA GENE SEQUENCE COMPARISONS1

Eight complete nuclear-encoded small-subunit ribosomal RNA (18S rRNA) gene sequences were determined for four genera of the Microthamniales (Pleurastrophyceae) and for Gloeotilopsis planctonica Iyengar & Philipose (Ulvophyceae, Ulotrichales) to investigate evolutionary relationships within the Microthamniales and the taxonomic position of this order within the green algae. Phylogenies inferred from these data revealed specific relationships at the level of genera and species that disagree with those inferred from vegetative cell morphology but agree with those inferred from motile cell characters. The rRNA phylogenies provide even better resolution than that gained from morphology alone. The coccoid lichen alga Trebouxia spp. is specifically related to other coccoid lichen and soil algae (i.e. Myrmecia biatorellae Boye-Petersen and Friedmannia israelensis Chantanachat & Bold), forming the “Lichen Algae Group,” an evolutionarily distinct lineage within the Microthamniales. Trebouxia is a paraphyletic and Pleurastrum a polyphyletic genus in rRNA phylogenies. In contrast to previous hypotheses based on morphology, Pleurastrum terrestre Fritsch & John is not closely related to Trebouxia but occupies an isolated position within the Microthamniales. The filamentous alga Microthamnion kuetzingianum is not ancestral to coccoid members of the Microthamniales but is closely related with the coccoid Fusochloris perforata (Lee & Bold) Floyd, Watanabe & Deason. The Microthamniales are inferred to be an array of independent lineages that radiate nearly simultaneously and may also include some autosporic coccoid taxa previously classified in the Chlorophyceae. Monophyly of the Microthamniales could not be demonstrated unequivocally. In contrast to a hypothesis based on ultrastructure, the Microthamniales are evolutionarily distinct from the Ulotrichales. The latter are ancestral to the radiation of the Microthamniales and the Chlorophyceae in the rRNA phylogenies.     

THE FLAGELLAR APPARATUS OF ENTOCLADIA VIRIDIS MOTILE CELLS,AND THE TAXONOMIC POSITION OF THE RESURRECTED FAMILY ULVELLACEAE (ULVALES,CHLOROPHYTA)1

The flagellar apparatuses of the quadriflagellate zoo-spores and biflagellate female gametes of the marine chaetophoracean alga Entocladia viridis Reinke are significantly different from those of algae belonging to Chaetophoraceae sensu stricto, but closely resemble those of ulvacean genera. These differences permit the taxonomic reassignment of certain marine chaetophoracean genera and an evaluation of the flagellar apparatus features used to characterize the class Ulvophyceae. Critical features of the zoospore include arrangement of the four basal bodies into an upper and a lower pair with the proximal ends of the upper basal bodies overlapping, terminal caps, proximal sheaths connected to one another by striated bands, and a cruciate microtubular rootlet system having a 3-2–3-2 alternation pattern and striated microtubule-associated components that accompany the two-membered rootlets. An indistinct distal fiber occurs just anterior to the basal bodies, and is closely associated with the insertion into the flagellar apparatus of the three-membered rootlets. The flagellar apparatus demonstrates 180° rotational symmetry, and its components show counterclockwise absolute orientation when viewed from above. Newly described features include the prominently bilobed structure of the terminal caps on the upper basal body pair, and the presence of both a granular zone and an additional single microtubule anterior to each of the four rootlets, an arrangement termed the “stacked rootlet configuration.” Rhizoplasts were not observed and are presumed to be absent. The gamete is identical, except for the absence of the lower basal body pair and the presence of an electron-dense membrane associated structure that resembles the mating structure found in Ulva gametes. These findings, correlated with life history data, sporangial and gametangial structure and developmental patterns, chloroplast pigment arrays, and vegetative cell ultrastructural features, compel the removal of Entocladia viridis and similar members of the marine Chaetophoraceae to a separate family, the Ulvellaceae. The latter is referred to the order Ulvales of the Ulvophyceae. The counterclockwise absolute orientation of components, and terminal caps, may be the most consistent flagellar apparatus features of ulvophycean green algae, while variations in other features previously considered diagnostic for the Ulvophyceae may serve instead to identify discrete lineages within this class.     

STRUCTURE AND ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS IN THE ISOGAMETES OF BATOPHORA (DASYCLADALES,CHLOROPHYTA)1

The overall appearance of the flagellar apparatus in the isogametes of Batophora oerstedii. J. Ag. is most like that which occurs in motile cells of the Ulvophyceae. Like other Ulvophyceae, the basal bodies overlap and are arranged in the 11/5 configuration, microtubular roots are arranged in a cruciate pattern and system II striated fibers are present. The basal body connective which generally lacks striation in the Ulvophyceae is clearly different in Batophora, being composed of two large non-striated halves which connect to the anterior surface of each basal body and are then connected to one another by a distinctly fibrous centrally striated region. This variation in the basal body connective and the presence of two posteriorly directed system II striated fibers is clearly different from homologous structures reported in siphonous green algae of the Caulerpales. Based upon these variations and similarities among flagellar apparatus components in siphonous green algae, it is suggested that the Dasycladales and Siphonodadales are more closely related to one another than to the Caulerpales.     

TWO SNOW SPECIES OF THE QUADRIFLAGELLATE GREEN ALGA CHLAINOMONAS (CHLOROPHYTA,VOLVOCALES): ULTRASTRUCTURE AND PHYLOGENETIC POSITION WITHIN THE CHLOROMONAS CLADE1

The quadriflagellate snow alga Chlainomonas Christen, distributed in New Zealand and North America, has several unusual structural attributes. A process assumed to be cytokinesis involves extrusion of protoplasm from the parent through a narrow canal, C. kolii (J. T. Hardy et Curl) Hoham produces a net‐like outer envelope rather than a cell wall, and the flagellar basal apparatus of Chlainomonas consists of two semi‐independent pairs of basal bodies. Structural connections between basal body pairs appear minimal, but a connecting system different from that observed in other genera exists within each pair. Phylogenetic analysis using rbcL sequences places Chlainomonas in the Chloromonas clade, other known members of which are all biflagellate. Chlainomonas is split into two robust lineages, with New Zealand collections sharing an origin with northern North American collections. Although the quadriflagellate condition is regarded as ancestral in the Chlorophyceae, we speculate—based on ultrastructural and molecular data presented here—that Chlainomonas represents a derived form that has arisen from fusion of two ancestral biflagellate cells. Other explanations (for example, that Chlainomonas represents a diploid form of a biflagellate species) are remotely possible but are presently at odds with extensive observations of field material. Improvements in techniques for experimental manipulation of these sensitive cryophiles will be required to fully characterize their structure and progress our understanding of their biology.     

OBSERVATIONS ON THE HABIT,MORPHOLOGY AND ULTRASTRUCTURE OF CEPHALEUROS PARASITICUS (CHLOROPHYTA) AND A COMPARISON WITH C. VIRESCENS1

Cephaleuros parasiticus Karsten, an endophyte of Magnolia grandiflora L. has been examined with light, and scanning and transmission electron microscopy. The discoid thalli are composed of filaments which ramify throughout the leaf tissues beneath the epidermis. Algal filaments do not penetrate host cells, but do produce black leaf spots which have been mistaken for those caused by the fungus Glomerella cingulate (Ston.) Spauld. and Schrenk. Two distinct thallus types occur, often simultaneously on a single leaf. One bears clusters of zoosporangiate branches which seasonally emerge through the ventral (and rarely, dorsal) surface of the leaf. In contrast, the other thallus type bears gametangia which break through the dorsal leaf surface. Zoosporangia and gametangia have never been found on the same thallus. The zoosporangia are smaller than, but almost identical in shape to, those of C. virescens Kunze. Simple plasmodesmata are present in crosswalls and acetolysis indicates that little or no sporopollenin is present in the cell walls. The ultrastructure of biflagellate gametes and quadriflagellate zoospores is virtually indistinguishable from that reported for C. virescens and similar to that reported for Phycopeltis and Trentepohlia. In both gametes and zoospores there are keeled flagella, overlapping and parallel basal bodies, two 3-layered multilayered structures with microtubular splines, and two medial compound microtubular roots. Pyrenoids, eyespots, flagellar and body scales, striated roots (or rhizoplasts), and distal bands are absent. Two presumptive mating structures are present in each biflagellate gamete, and flagellar collars occur in both types of motile cells. The extreme similarity in motile cell ultrastructure revealed in this interspecific comparison parallels that similarity revealed in intergeneric comparisons.     

ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS OF PTEROSPERMA CRISTATUM (PRASINOPHYCEAE) AND CONSIDERATION OF ITS PHYLOGENETIC POSITION1

Pterosperma cristatum Schiller, a member of the Pra-sinophyceae, was examined with light and electron microscopy with special attention on the absolute configuration of flagellar apparatus components and associated structures. This alga is characterized by asymmetrically arranged basal bodies, connecting fibers and microtubular roots. The microtubular root system is homologous with the cruciate root system, the so-called X-2-X-2 root system typical of non-charophycean green algae. Two ducts are associated with microtubular roots. A similar flagellar apparatus and duct system was found in two other prasinophyte genera, Pyramimonas and Halosphaera. The close phylogenetic affinity of these three genera is discussed.     

ULTRASTRUCTURE AND PHYLOGENETIC RELATIONSHIPS OF CHAETOPELTIDALES ORD. NOV. (CHLOROPHYTA,CHLOROPHYCEAE)1

Vegetative cells and zoospores of Hormotilopsis gelatinosa Trainor & Bold, H. tetravacuolaris Arce & Bold, Planophila terrestris Groover & Hofstetter, and Phyllogloea fimbriata (Korchikov) Silva were examined by transmission electron microscopy. All cells had pyrenoids traversed by cytoplasmic channels. Zoospores were quadriflagellate and had essentially cruciate flagellar apparatuses. Scales were present on free-swimming zoospores. These features are essentially identical to those of Chaetopeltis sp. and are dissimilar to those of other described green algae. The new order Chaetopeltidales is created to accommodate the genera Chaetopeltis, Hormotilopsis, Planophila sensu Groover & Hofstetter, Phyllogloea, Dicranochaete, and Schizochlamys, organisms previously scattered among the orders Tetrasporales, Chloro-coccales, Chlorosarcinales, and Chaetophorales. Members of the order are closely related to the ancestral chlorophycean flagellate genus Hafniomonas, may be ancestral with respect to other Chlorophyceae, and may also be closely related to the ulvophycean order Ulotrichales.     

INFERRING TAXONOMIC POSITIONS AND TESTING GENUS LEVEL ASSIGNMENTS IN COCCOID GREEN LICHEN ALGAE: A PHYLOGENETIC ANALYSIS OF 18S RIBOSOMAL RNA SEQUENCES FROM DICTYOCHLOROPSIS RETICULATA AND FROM MEMBERS OF THE GENUS MYRMECIA (CHLOROPHYTA, TREBOUXIOPHYCEAE CL. NOV.)1

Complete nuclear-encoded small-subunit ribosomal RNA (18S rRNA) coding sequences were determined for the coccoid green algae Dictyochloropsis reticulata (Tschermak-Woess) Tschermak-Woess , Myrmecia astigmatica Vinatzer, and M. bisecta Reisigl, to investigate the taxonomic position of Dictyochloropsis Geitler and of the genus Myrmecia Printz. Phylogenies inferred from these data revealed a sister-group relationship between D. reticulata and certain coccoid green algae that lack motile stages (autosporic coccoids) within the order Microthamniales. The monophyletic origin of the Microthamniales, including autosporic coccoids previously classified in the Chlorophyceae, is clearly resolved by the rRNA sequence data. This finding. shows the considerable taxonomic breadth of that order, whose taxonomic position has been unclear so far. A new class, Trebouxiophyceae, is proposed for this group of green algae. Phylogenetic inferences from the rRNA sequences show paraphyly of the genus Myrmecia. The 18S rRNA sequence data suggest that, among taxa that share similar vegetative cell morphologies, the zoospore characters resolve better the actual genus and species boundaries. Within identical zoospore types, the rRNA data allow further resolution of taxonomic relationships. On the basis of the.se findings, I propose that the genus Friedmannia Chantanachat ± Bold be merged into Myrmecia and that only those species be left in the genus Myrmecia that are identical in particular zoospore characters (i.e. those described in detail for M. israeliensis ( Chantanachat ± Bold) comb, nov.), namely M. astigmatica, M. biatorellae (Tschermak-Woess ± Ptesst) Petersen, and M. israeliensis. Myrmecia bisecta has to be excluded from Myrmecia; its taxonomic position within the Trebouxiophyceae is unclear .     

尼氏单极虫(粘体门,双壳目)重描述及基于18S rDNA系统地位分析

采用常规细胞学方法与18S rDNA序列比较的方法,对采自于重庆市嘉陵江段的粘孢子虫,尼氏单极虫Thelohanellus nikolskii进行了形态学和分子生物学的研究,此为首次在我国长江流域检获尼氏单极虫。本文在补充了尼氏单极虫中国种群18S rDNA序列信息的分析、比较基础上,探讨了该虫与相邻种属的系统关系,佐证了其分类学位置。