Schizocladia ischiensis: a new filamentous marine chromophyte belonging to a new class,Schizocladiophyceae

A new marine filamentous chromophyte Schizocladia ischiensis sp. nov. is described from Naples, Italy, and a new class, Schizocladiophyceae, is proposed to accommodate the species based on morphology, photosynthetic pigment analysis, and rbcL and 18S rRNA gene sequences. The vegetative thallus is composed of branched filaments, 3-7 microm in diameter, containing one to two light brown parietal plastids. Cell walls are composed of layered fibers containing alginates, but lacking cellulose. Plastids are of the typical chromophyte type, containing chlorophylls a and c, and abundant fucoxanthin. Zoospores are formed by direct transformation of vegetative cells or through a process including a multinucleated cell stage. Zoospores are teardrop-shaped with a longer anterior flagellum with tubular mastigonemes and a shorter smooth posterior flagellum with a basal swelling. Flagella have a single basal plate and multi-gyred transitional helix distal to the basal plate. Each zoospore has an eyespot. Phylogenetic analyses using rbcL and 18S rDNA sequences suggest the closest phylogenetic relationship with Phaeophyceae, and then with Xanthophyceae and Phaeothamniophyceae. Nevertheless, Schizocladia differs from Phaeophyceae in some essential features (i.e. cell wall lacking cellulose and plasmodesmata, presence of flagellar transitional helix). Therefore, an independent class Schizocladiophyceae is proposed to accommodate this new taxon.     

The chloroplast pigments of the algal classes Eustigmatophyceae and Xanthophyceae. II. Xanthophyceae

The chloroplast pigments of Pleurochloris meiringensis Vischer, Mischococcus sphaerocephalus Vischer and Tribonema aequale Pascher have been analysed by a variety of chromatographic methods. There are significant differences between these xanthophycean algae and the eustigmatophycean algae formerly classified with them. In particular the former contain diadinoxanthin as the major xanthophyll whereas diadinoxanthin is absent from the latter and violaxanthin occurs as the major xanthophyll pigment. The other pigments of the Xanthophyceae sensu stricto include chlorophyll a, β-carotene, vaucheriaxanthin-ester, heteroxanthin, diatoxanthin, cryptoxanthin epoxide and a neoxanthin-like pigment.     

Heteroxanthin in Euglena gracilis

Summary 1. From a large scale preparation of Euglena gracilis, strain Z, besides the acetylenic pigments diatoxanthin and diadinoxanthin and the allene neoxanthin, an additional acetylenic xanthophyll has been isolated. 2. Mass and IR spectra and chemical reactions showed typical patterns of heteroxanthin from Vaucheria. 3. The pigment was transformed into diadinochrome-isomers with acidified acetone. 4. A partial synthesis of heteroxanthin from diadinoxanthin by LiAlH₄-reduction is described, confirming the structure proposed by Strain. 5. The identity of heteroxanthin with the trollein—like pigment described for Euglena is discussed.     

The structure and phylogenetic significance of the flagellar transition region in the chlorophyll c-containing algae.

An electron-dense helix is the most conspicuous structure in the flagellar transition region of members of the algal class Chrysophyceae. This “transitional helix” (TH) lies immediately distal to a partition across the flagellar axoneme which occurs exactly at the level at which the flagellum enters the cell body. The helix surrounds the central axonemal pair and lies at a distance of 10 nm from the 9 peripheral doublets. From the new data presented and a survey of published observations on the structure of the transition region of all the chlorophyll c-containing classes of algae, it is shown that a TH characteristic of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae. The number of TH gyres varies from 3 to 6 in the Xanthophyceae and from 1 to 8 in the Chrysophyceae. In any one species, however, the TH is the same size in both the long flagellum which bears tubular mastigonemes and in the short smooth flagellum, though in some chrysophytes where the short flagellum is vestigial the number is fewer than in the normal flagellum. A TH appears to be absent from the Rhaphidophyceae and zoids of the Bacillariophyceae and Phaeophyceae though the structure of the transition region in these groups otherwise resembles that of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae.The value of transition region variation in determining evolutionary relationships among the chlorophyll c-containing algal classes is assessed against a background of current ideas on their taxonomy and phylogeny. The relevant structural and biochemical features are tabled, and a phylogenetic scheme is presented which appears most logically to interpret these data. It is suggested that the line leading to the Eustigmatophyceae probably diverged from that leading to the strictly heterokont classes Xanthophyceae, Chrysophyceae, Phaeophyceae and Bacillariophyceae before evolution of a girdle lamella in the chloroplast and a photoreceptor apparatus involving a swelling at the proximal end of the short flagellum and an intraplastidial eyespot. The possession of a TH by both the Chrysophyceae and Xanthophyceae adds further support to the concept of their close relationship based on a range of other features. The exceptional absence of a TH from the chrysophycean genera Pedinella and Pseudopedinella reinforces the idea that these taxa are remote from the main chrysophycean line. Absence of a TH from the Phaeophyceae and Bacillariophyceae which otherwise share many important features with the Chrysophyceae and Xanthophyceae is probably a result of loss owing to the functional and morphological specialization of the zoids of these two groups. Transition region structure does not clarify the possible relationships of the Rhaphidophyceae, Prymnesiophyceae, Cryptophyceae or Dinophyceae.The proposed phylogeny supports the idea of a mutually related “heterokont” protist assemblage comprising the Chrysophyceae, Xanthophyceae, Phaeophyceae, Bacillariophyceae and possibly Rhaphidophyceae and the Oomycetes (water moulds) though in the latter the TH is replaced by a dense cylinder with a corrugated wall which may or may not be homologous with it. Structures resembling a TH have been described in a wide variety of other flagellated cells including the prasinophyte Pyraminonas orientalis, one species of the colourless flagellate genus Bicosoeca and the proteromonads Karotomorpha and Proteromonas. Only in the latter genera does homology with a TH seem likely on present evidence, suggesting that flagellates of this type may have evolved from chrysomonad-like ancestors.     

Immunogold-labeling analysis of alginate distributions in the cell walls of chromophyte algae

The immunogold electron microscopy technique was employed to detect the presence of alginates in the cell walls of selected chromophyte species. Anti-alginate antiserum labeled the cell walls of Sphacelaria and Scytosiphon (Phaeophyceae), Tribonema, Vaucheria, Botrydium, Botrydiopsis (Xanthophyceae) and an‘un-described filamentous species’ (incertae cedis), but it did not label those of Giraudyopsis, Phaeosaccion (Chrysomeridales), Antithamnion (Rhodophyceae) and Bryopsis (Ulvophyceae). This is the first report of the occurrence of alginates in the chromophyte outside Phaeophyceae. The absence of alginates in Chrysomeridales, which has an unclear phylogenetic position, implies a rather distant phylogenetic relationship of the order Chrysomeridales from Phaeophyceae/Xanthophyceae.     

ISOLATION AND CHARACTERIZATION OF PARMALES (HETEROKONTA/HETEROKONTOPHYTA/STRAMENOPILES) FROM THE OYASHIO REGION,WESTERN NORTH PACIFIC1

A small siliceous species of marine phytoplankton, order Parmales (Heterokonta), was isolated and characterized for the first time with the aid of a fluorescent silicon tracer 2‐(4‐pyridyl)‐5‐([4‐(2‐dimethylaminoethylaminocarbamoyl)‐methoxy]phenyl)oxazole (PDMPO). This dye was easily detected by clear fluorescence in newly produced silica cell plates. Our isolate was surrounded by eight smooth plates without any ornamentation, suggesting a similarity to Triparma laevis B. C. Booth. TEM observation showed the typical ultrastructure of photosynthetic heterokontophytes; with two chloroplast endoplasmic reticulate membranes, a girdle lamella, three thylakoid lamellae, and mitochondrion with tubular cristae. Molecular phylogenetic analyses of SSU rDNA and rbcL genes showed that the parmalean alga was within the bolidophycean clade of autotrophic naked flagellates and a sister group of diatoms. HPLC analysis detected chl a, c₁ + c₂, and c₃; fucoxanthin; and diadinoxanthin as major photosynthetic pigments, and a composition that is shared with Bolidophyceae and diatoms. Together, these data indicate a close evolutionary relationship between Parmales, Bolidophyceae, and diatoms. The PDMPO‐staining procedure should accelerate isolation of other Parmales species, helping to establish their diversity and aiding quantitative study of their role in oceanic processes.     

Absolute orientation of the flagellar apparatus of Hibberdia magna comb. nov. (Chrysophyceae)

The first flagellum of Hibberdia magna comb. nov. bears mastigonemes that have both short and long lateral filaments attached to the tubular shaft. The second flagellum is very short (ca. 850 nm) and is directed posteriorly approximately 160° from the first flagellum. Three microtubular flagellar roots (R₁, R₂ and R₄) and a rhizoplast (= striated root) are present. The R₁ root consists of four microtubules that arise near the right surface of the first flagellum basal body; the R₁ root extends to the dorsal side of the cell and then curves back along the left side of the cell. Cytoskeletal microtubules are nucleated from the R₁ root including one loose cluster of cytoskeletal microtubules that extends down the left side of the cell adjacent to the contractile vacuole. The R₂ root is a single microtubule that arises along the left surface of the first flagellum basal body and extends to the left side of the cell. The R₄ root consists of three microtubules that arise along the left side of the second flagellum basal body. A helical band wraps around two microtubules at the proximal end of the R₄ root. Two of the three R₄ root microtubules extend along the left side of the second flagellum, curve around to the right side of that flagellum and terminate. No R₃ root was found. The orientation of the basal bodies of Hibberdia gen. nov. is similar to that of the Xanthophyceae and Oomycetes. There are apparent homologies in the R₁, R₂ and R₄ roots of Hibberdia and these and other protists, but only Hibberdia lacks a R₃ root. Three long flagella are present in preprophase but later one is endocytosized and the axoneme extends to the posterior of the cell. During metaphase the nuclear envelope is more or less intact except at the poles; the flagellar apparatuses are at the poles and the spindle microtubules originate near the basal bodies. Two stages are known in the life history: 1) a capsoidlike state with non-swimming flagellate cells inside a colonial gel, and 2) a free-swimming single-celled monad state. Vegetative cell division occurs in both stages. The flagellar apparatus, the cell division process and the life history combined with the previously described unique light-harvesting antheraxanthin make H. magna distinct from other algae. A new genus, Hibberdia gen. nov., a new family, Hibberdiaceae fam. nov. and a new order, Hibberdiales, ord. nov. are described.     

Morphological convergence characterizes the evolution of Xanthophyceae (Heterokontophyta): evidence from nuclear SSU rDNA and plastidial rbcL genes

Xanthophyceae are a group of heterokontophyte algae. Few molecular studies have investigated the evolutionary history and phylogenetic relationships of this class. We sequenced the nuclear-encoded SSU rDNA and chloroplast-encoded rbcL genes of several xanthophycean species from different orders, families, and genera. Neither SSU rDNA nor rbcL genes show intraspecific sequence variation and are good diagnostic markers for characterization of problematic species. New sequences, combined with those previously available, were used to create different multiple alignments. Analyses included sequences from 26 species of Xanthophyceae plus three Phaeothamniophyceae and two Phaeophyceae taxa used as outgroups. Phylogenetic analyses were performed according to Bayesian inference, maximum likelihood, and maximum parsimony methods. We explored effects produced on the phylogenetic outcomes by both taxon sampling as well as selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on a data set including both SSU rDNA and rbcL sequences. Trees obtained in this study show that several currently recognized xanthophycean taxa do not form monophyletic groups. The order Mischococcales is paraphyletic, while Tribonematales and Botrydiales are polyphyletic even if evidence for the second order is not conclusive. Botrydiales and Vaucheriales, both including siphonous taxa, do not form a clade. The families Botrydiopsidaceae, Botryochloridaceae, and Pleurochloridaceae as well as the genera Botrydiopsis and Chlorellidium are polyphyletic. The Centritractaceae and the genus Bumilleriopsis also appear to be polyphyletic but their monophyly cannot be completely rejected with current evidence. Our results support morphological convergence at any taxonomic rank in the evolution of the Xanthophyceae. Finally, our phylogenetic analyses exclude an origin of the Xanthophyceae from a Vaucheria-like ancestor and favor a single early origin of the coccoid cell form.     

Observations on the ultrastructure of the flagella and periplast in the Cryptophyceae

The flagella in Cryptomonas ovata Ehrenberg and two other un-named strains of Cryptomonas both bear stiff hairs with fine distal filaments of the same type as those found in the Xanthophyceae, the Chrysophyceae sensu stricto, the Phaeophyceae, the Bacillariophyceae, the Eustigmatophyceae and the Oomycetes. On the longer of the two flagella the hairs are 2·5 µm long and in two opposite rows whereas on the shorter flagellum they measure only 1 µm, are arranged in a single row and are more closely spaced. The long flagellum also bears a characteristic lateral swelling with a tuft of hairs of the same type as on the remainder of the flagellum, at approximately the level at which it emerges from the gullet. The hairs on the flagella of Hemiselmis rufescens Parke are distributed in a similar manner to those in Cryptomonas but they are more flexible and the swelling and tuft of hairs appear to be absent from the long flagellum. Hairs are apparently absent from the short flagellum of Chroomonas sp. The periplast in Cryptomonas ovata shows a hexagonal pattern in surface view and in sections of all three Cryptomonas strains appears as a typical plasmalemma underlain by a discontinuous layer of electron-dense material with variable substructure. The distribution of flagellar hairs and the structure of the periplast appear to be characters unique to the Cryptophyceae and these features emphasise the isolated position of this class of algae.     

A "Total Evidence" Analysis of the Phylogenetic Relationships among the Photosynthetic Stramenopiles

Phylogenetic relationships among the nine major autotrophic stramenopile taxa were inferred in a combined analysis of the rbcL, SSU rDNA, partial LSU rRNA, carotenoid, and ultrastructural data sets. The structure of the shortest combined tree is: (Outgroup, ((((Bacillariophyceae, (Pelagophyceae, Dictyochophyceae)),((Phaeophyceae, Xanthophyceae), Raphidophyceae)), Eustigmatophyceae),(Chrysophyceae, Synurophyceae))). The Synurophyceae/Chrysophyceae is the best supported group followed by the Phaeophyceae/Xanthophyceae and the Pelagophyceae/Dictyochophyceae clades. The monophyletic groups composed of Bacillariophyceae/Pelagophyceae/Dictyochophyceae and Phaeophyceae/Xanthophyceae/Raphidophyceae received the lowest Bremer support values. The optimal combined tree suggests that the diatom frustule is derived from the siliceous "skeleton" in Dictyochophyceae, that the reduced flagellar apparatus arose once in the Bacillariophyceae/Dictyochophyceae/Pelagophyceae clade, and that the specific photoreceptor-eyespot apparatus in Chrysophyceae and the Phaeophyceae/Xantophyceae clade originated independently within the autotrophic stramenopiles. Despite conflicts in tree structure between the most-parsimonious combined phylogeny and the optimal tree(s) of each data partition, it cannot be concluded that extensive incongruence exists between the data sets.     

A NEW PHYLOGENY FOR CHROMOPHYTE ALGAE USING 16S-LIKE RRNA SEQUENCES FROM MALLOMONAS PAPILLOSA (SYNUROPHYCEAE) AND TRIBONEMA AEQUALE (XANTHOPHYCEAE)1

The 16S-like ribosomal RNA genes from Mallomonas papillosa Harris et Bradley (Synurophyceae) and Tribonema aequale Pascher (Xanthophyceae) were sequenced and compared to those of other eukaryotes. Mallomonas is closely related to Ochromonas (Chrysophyceae) and supports the general hypothesis of a close phylogenetic relationship between the Synurophyceae and Chrysophyceae. Tribonema is specifically related to Costaria costata (C. A. Agardh) Saunders (Phaeophyceae) demonstrating an unexpected phylogenetic relationship between the Xanthophyceae and Phaeophyceae. Distance and parsimony analysis place these four chromophyte genera in a complex evolutionary assemblage that includes the Bacillariophyceae and Oomycetes but excludes the Dinophyceae. The close relationship between the chromophyte algae and the Öomycete fungi supports the hypothesis that protists with tripartite hairs form a natural assemblage.     

CYTOLOGICAL AND PHYLOGENETIC DIVERSITY IN FRESHWATER ESOPTRODINIUM/BERNARDINIUM SPECIES (DINOPHYCEAE)1

The genera Esoptrodinium Javornický and Bernardinium Chodat comprise freshwater, athecate dinoflagellates with an incomplete cingulum but differing reports regarding cingulum orientation and the presence of chloroplasts and an eyespot. To examine this reported diversity, six isolates were collected from different freshwater ponds and brought into clonal culture. The isolates were examined using LM to determine major cytological differences, and rDNA sequences were compared to determine relatedness and overall phylogenetic position within the dinoflagellates. All isolates were athecate with a left‐oriented cingulum that did not fully encircle the cell, corresponding to the current taxonomic concept of Esoptrodinium. However, consistent cytological differences were observed among clonal isolates. Most isolates exhibited unambiguous pale green chloroplasts and a distinct bright‐red eyespot located at the base of the longitudinal flagellum. However, one isolate had cryptic chloroplasts that were difficult to observe using LM, and another had an eyespot that was so reduced as to be almost undetectable. Another isolate lacked visible chloroplasts but did possess the characteristic eyespot. Nuclear rDNA phylogenies strongly supported a monophyletic Esoptrodinium clade containing all isolates from this study together with a previous sequence from Portugal, within the Tovelliaceae. Esoptrodinium subclades were largely correlated with cytological differences, and the data suggested that independent chloroplast and eyespot reduction and/or loss may have occurred within this taxon. Overall, the isolates encompassed the majority of cytological diversity reported in previous observations of Bernardinium/Esoptrodinium in field samples. Systematic issues with the current taxonomic distinction between Bernardinium and Esoptrodinium are discussed.     

ON PIGMENTS,GROWTH, AND PHOTOSYNTHESIS OF PHAEODACTYLUM TRICORNUTUM12

A maximum growth rate with doubling time of 18 hr at 18 C could be maintained. Continuous cultures at about half maximum growth rate provided cells for study of pigments and photosynthesis. The light intensity curve of photosynthesis had no unusual features and showed light-saturated rates of 30-35 μl O₂/mrn³-hr at 18 C. Pigment analysis showed chlorophylls a and c (a/c ratio = 4), fucoxanthin, β-carotene, and diadinoxanthin. Growth under red light (±660 mμ) altered pigments only by decrease in chlorophyll c to about one-half the content obtained under clear tungsten lamps. The large and anomalous spectral shift in fucoxanthin following organic solvent extraction runs confirmed, but efforts to isolate a native fucoxanthin were unsuccessful. Spectral analysis of acetone extracts and sonicated cell preparations allowed estimate of fractional absorption by each component pigment. The analysis shows that chlorophyll a and fucoxanthin are the principal light absorbing pigments and that absorption by other carotenoids is very small.     

PSEUDULVELLA AMERICANA BELONGS TO THE ORDER CHAETOPELTIDALES (CLASS CHLOROPHYCEAE), EVIDENCE FROM ULTRASTRUCTURE AND SSU RDNA SEQUENCE DATA1

The genus Pseudulvella Wille 1909 includes epiphytic, freshwater, or marine disk‐shaped green microalgae that form quadriflagellate zoospores. No ultrastructural or molecular studies have been conducted on the genus, and its evolutionary relationships remain unclear. The purpose of the present study is to describe the life history, ultrastructural features, and phylogenetic affiliations of Pseudulvella americana (Snow) Wille, the type species of the genus. Thalli of this microalga were prostrate and composed of radiating branched filaments that coalesced to form a disk. Vegetative cells had a pyrenoid encircled by starch plates and traversed by one or two convoluted cytoplasmic channels. They had well‐defined cell walls without plasmodesmata. Asexual reproduction was by means of tetraflagellate zoospores formed in numbers of two to eight from central cells of the thallus. The flagellar apparatus of zoospores was cruciate, with four basal bodies and four microtubular roots. The paired basal bodies lay directly opposite (DO) one another. The microtubular root system had a 5‐2‐5‐2 alternation pattern, where the “s” roots contained five microtubules in a four‐over‐one configuration. A tetralobate nonstriated distal fiber connected all four basal bodies. A wedge‐shaped proximal sheath subtended each of the basal bodies. The ultrastructural features of the zoospores were those of members of the order Chaetopeltidales. Phylogenetic analyses based on SSU rDNA placed P. americana sister to Chaetopeltis orbicularis in a well‐supported Chaetopeltidales clade. Such a combination of features confirmed that this alga is a member of the order Chaetopeltidales.     

The response of carotenoids and chlorophylls during virus infection of Emiliania huxleyi (Prymnesiophyceae)

We report the response of carotenoids and chlorophylls during 120 h time series virus infection experiments of the marine coccolithophorid Emiliania huxleyi (Lohm.) Hay et Mohler culture. The response of individual carotenoids to infection varied: Diatoxanthin (Dtx) increased rapidly relative to chlorophyll-a, whereas diadinoxanthin (Ddx) and β-carotene showed a rapid decrease and fucoxanthin and 19′hexanoyloxyfucoxanthin a slight increase. The response of the individual carotenoids reflects their role in epoxy/de-epoxidation cycling, antioxidant protection, biosynthetic conversion and vulnerability to photooxidative destruction. We observed for the first time the operation of the diadinoxanthin cycle occurring in response to viral infection in E. huxleyi with the de-epoxidation ratio (Dtx / (Dtx + Ddx)) increasing exponentially with time (R² = 0.92) and decreasing exponentially with F_V / F_M (R² = 0.97). Our findings contribute to our understanding of the conversion and fate of key biochemical cell constituents in algae and are important in understanding the physiological stress response to virus infection.     

PIGMENT SIGNATURES AND PHYLOGENETIC RELATIONSHIPS OF THE PAVLOVOPHYCEAE (HAPTOPHYTA)1

Variations in the HPLC‐derived pigment composition of cultured Pavlovophyceae (Cavalier‐Smith) Green et Medlin were compared with phylogenetic relationships inferred from 18S rDNA sequencing, morphological characteristics, and current taxonomy. The four genera described for this haptophyte class (Diacronema Prauser emend. Green et Hibberd, Exanthemachrysis Lepailleur, Pavlova Butcher, and Rebecca Green) were represented by nine different species (one of which with data from GeneBank only). Chlorophylls a, c₁, c₂ and MgDVP (Mg‐[3,8‐divinyl]‐phytoporphyrin‐13²‐methylcarboxylate) and the carotenoids fucoxanthin, diadinoxanthin, diatoxanthin, and β,β‐carotene were detected in all cultures. Species only differed in the content of an unknown (diadinoxanthin‐like) xanthophyll and two polar chl c forms, identified as a monovinyl (chl c₁‐like) and a divinyl (chl c₂‐like) compound. This is the first observation of the monovinyl form in haptophytes. Based on distribution of these two chl c forms, species were separated into Pavlovophyceae pigment types A, B, and C. These pigment types crossed taxonomic boundaries at the generic level but were in complete accordance with species groupings based on molecular phylogenetic relationships and certain ultrastructural characteristics (position and nature of pyrenoid, stigma, and flagella). These results suggest that characterization of the pigment signature of unidentified culture strains of Pavlovophyceae can be used to predict their phylogenetic affinities and vice versa. Additional studies have been initiated to evaluate this possibility for the haptophyte class Prymnesiophyceae.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF UROGLENA AMERICANA (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Uroglena americana Calkins (Uroglenopsis americana [Calkins] Lemmerman) was determined using serial section reconstruction. The three microtubular rootlet systems (R₂, R₃, and R₄) follow the general pattern found in other chrysophytes. The R₂ rootlet originates between the basal bodies of the mastigoneme-bearing long flagellum (F₁) and the short smooth flagellum (F₂) and is attached to the former by a fibrous connection. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts (designated R₃ and R₃) which circle the depression from which the F₂ flagellum emerges in counter-clockwise direction. These two rootlets pass beneath the F₂ basal body and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material which passes diagonally over the F₂ basal body, forms a clockwise loop about three-quarters of the way around the depression, and ends in the cytoplasm. In place of a typical chrysophyte R₁ rootlet, U. americana has a different array of microtubules attached to the F₁ basal body which we have designated the descending rootlet (DR). This rootlet is a hairpin-shaped structure lying just below the surface of the cell; its longitudinal axis is predominantly parallel to the longitudinal axis of the cell. The DR resembles the bypassing rootlet which occurs in phaeophyte zoospores. Other chrysophytes may possess rootlets which are similar to the DR found in Uroglena.     

THE FLAGELLAR APPARATUS OF CHRYSOLEPIDOMONAS DENDROLEPIDOTA (CHRYSOPHYCEAE), A SINGLE-CELLED MONAD COVED WITH ORGANIC SCALES1

The flagellar apparatus of Chrysolepidomonas dedrolepidota Peters et Andersen is similar to that of other members of the Ochromonadales, Chrysophyceae. there are four microtubular roots (R_1-4) and a system II fiber (= rhizoplast). the R₁ root consists of three microtubules that nucleate many cytoplasmic microtubules. One compressed band of 10 or more cytoplasmic microtubules is directed black along the R1 root in an anti-parallel direction. The R₂ root consists of one to two microtubules, and it extends toward the distal end of the R₁ root. The R₃ root consists of six (?seven) microtubules near its proximal end. The “a” and “f” microtubules of the R₃ root are under the short flagellum, and the “f” microtubule loops back and under the basal body, extending down to the nucleus. The R₄ root consists of one to two microtubules extending along the left side of the shot flagellum and curving under the short flagellum where it terminates near the “a” microtubule of R₃ Both flagella have a transitional plate and a transitional helix with five gyres. There is a thin, second plate in the basal body at the level of the distal end of the “c” tubules of the basal body triplets. The tripartite flagellar hairs have long lateral filaments but lack short lateral filaments. We compare the flagellar apparatus with that of other members of the Ochromonadales and members of the Hydrurales and Hibberdiales.     

CYTOLOGY AND ULTRASTRUCTURE OF CHLORARACHNION REPTANS (CHLORARACHNIOPHYTA DIVISIO NOVA,CHLORARACHNIOPHYCEAE CLASSIS NOVA)1

The green amoeboid cells of Chlorarachnion reptans Geitler are completely naked and each contains a central nucleus, several bilobed chloroplasts each with a central projecting pyrenoid enveloped by a capping vesicle, several Golgi bodies, mitochondria with tubular cristae, extensive rough ER, and a distinct layer of peripheral vesicles. Complex extrusome-like organelles occur rarely in both the amoeboid and flagellate stages. The only organelles entering the reticulopodia are mitochondria, but microtubules are also present. The chloroplasts contain chlorophylls a and b, but histochemical tests suggest that the carbohydrate storage product probably is not a starch. The chloroplast lamellae are composed of one to three thylakoids or form deep stacks. A girdle lamella and interlamellar partitions are absent. Each chloroplast is bounded by either four separate membranes, a pair of membranes with vesicular profiles between them, or three membranes; all three arrangements may occur in the same chloroplast. A periplastidal compartment occurs near the base of the pyrenoid where there are always four surrounding membranes. The compartment has a relatively dense matrix and contains ribosome-like particles and small dense spheres; it extends over and into a deep invagination in the pyrenoid where its contents are enclosed in a double-membraned envelope which is penetrated by wide pores. The zoospores are ovoid and each bears a single laterally inserted flagellum which appears to be wrapped helically around the cell body during swimming. The flagellum lies in a groove in the cell surface and bears fine lateral hairs. Neither a second flagellum or vestige of one, nor an eyespot, is present. A single microtubular root and a larger homogeneous root run from the flagellar base parallel to the emerging flagellum, between the nuclear envelope and the plasmalemma. In the simple flagellar transition region, fine filaments connect adjacent axonemal doublets. A detailed comparison of C. reptans with all other algal taxa results in the conclusion that it must be segregated in the new class Chlorarachniophyceae, the only class in the new division Chlorarachniophyta. The possibility that C. reptans evolved from a symbiosis between a colorless amoeboid cell and a chlorophyll b- containing eukaryote is considered, but the possible affinities of the symbiont remain enigmatic. The implications of the unique chloroplast structure of C. reptans for current hypotheses concerning the origin of chloroplasts are discussed.