SECRETION AND DEPLOYMENT OF BRISTLES IN MALLOMONAS SPLENDENS (SYNUROPHYCEAE)1

Mallomonas splendens (G. S. West) Playfair has a cell covering of siliceous scales and bristles. Interphase cells bear four anterior and four posterior bristles that each articulate, at their flexed basal ends via a complex of labile fibers (the fibrillar complex), on a specialized body scale (a base-plate scale). Body scales, base-plate scales and bristles are formed independently of each other and at different times in silica deposition vesicles (SDVs) that are associated with one of the two chloroplasts. The fine structure of scale and bristle morphogenesis in M. splendens agrees with that previously described for Synura and Mallomonas. Four new posterior bristles are formed at late interphase with their basal ends towards the cell posterior. The fibrillar complex is formed in situ on the bristle in the SDV. Mature bristles are secreted one by one onto the surface of the protoplast, beneath the layer of body scales, where the basal ends of the bristles adhere to the plasma membrane via the fibrillar complex. The extrusion of posterior bristles and their deployment onto the cell surface was monitored with video. A fine cellular protuberance accompanies the bristles as they are extruded from beneath the scale layer with their basal ends leading. When distant from the cell, the basal ends of the bristles appear attached to the protuberance, possibly by way of their fibrillar complexes. Once bristles are fully extruded, and their tips free in the surrounding environment, the bristle bases are drawn back to the posterior apex of the cell, apparently by the now shortening protuberance. Thus a 180° reorientation of the posterior bristles has been effected outside the cell. Thin-sections of cells that are extruding bristles show a threadlike, cytoplasmic extension of the cell posterior which may be analogous to the protuberance seen in live cells. Four new posterior base-plate scales are secreted after the bristles have reoriented. Scanning electron microscopy indicates that the fibrillar complex is involved in positioning the bristles onto their respective base-plate scales. Anterior bristles are formed in new daughter cells in the same orientation as the posterior bristles; thus they are extruded tip first and no reorientation is required.     

THE FINE STRUCTURE AND SCALE FORMATION OF CHRYSOLEPIDOMONAS DENDROLEPIDOTA GEN. ET. SP. NOV.(CHRYSOLEPIDOMONADACEAE FAM. NOV., CHRYSOPHYCEAE)1

Chrysolepidomonas gen. nov. is described for single-celled monads with two flagella, a single chloroplast, and distinctive canistrate and dendritic scales. The type species, Chrysolepidomonas dendrolepidota sp. nov., is described for the first time. The canistrate scales bear eight “bumps” on the top surface, and the dendriticscales have a tapered base with a quatrifid tip. These organic scales are formed in the Golgi apparatus and storred in a scale reservoir. The scale reservoir is bounded on two sides by the R₁ and R₂ in microtubular roots of the basal apparatus. The cyst (=stomatocyst, statospore) forms endogenously by means of a silica deposition vesicle. The outer cyst surface is smooth, and the pore region is unornamented. Two other organisms bearing canistrate and dendritic scales, previously assigned to the genus Sphaleromants, are transferred to the genus Chrysolepidomonas. They are C.angalica sp. nov. and C. marine(Pienaar) comb. nov. The distinguishing features of Chrysolepidomonas and Sphaleromantis are discussed. A new family, Chrysolepidomonadceae fam. noc., is described for flagellates covered with organic scales.     

CURRENT KNOWLEDGE OF THE LIFE CYCLES OF PHAEOCYSTIS GLOBOSA AND PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE)1

Despite continuous efforts since the 1950s and more recent advances in culturing flagellates and nonflagellate cells of the prymnesiophyte Phaeocystis, a number of different life‐cycle models exist today that appear to apply for P. globosa Scherff. and P. antarctica G. Karst., both spherical colony formers. In one such model, this life cycle consists of three different flagellates and one nonmotile cell stage that is embedded in carbohydrate matrix‐forming colonies of different sizes and forms. Recently, noncolonial aggregates of diploid nonmotile cells attached to surfaces of diatoms were put forward as a new stage in the sexual life cycle of P. antarctica. However, it can be discussed that these “attached aggregates” (AAs) are an intermediate between motile diploid flagellates, with their well‐known tendency to adhere to surfaces, and the young spherical colony with its diploid nonmotile cells, which in nature is commonly found attached to diatoms. A life‐cycle model pertaining to both P. globosa and P. antarctica is presented.     

CELL DIVISION IN THE SCALY GREEN FLAGELLATE HETEROMASTIX ANGULATA AND ITS BEARING ON THE ORIGIN OF THE CHLOROPHYCEAE

H. angulata is a scale-covered, asymmetrical green unicell with two laterally attached, anisokont flagella. In recent years it has been classified in the Prasinophyceae. The flagellar apparatus replicates, and the cell begins to cleave at the side opposite the flagella before the nucleus can be perceived to be in prophase. The flagellar apparatuses separate, and the extra-nuclear development of the spindle occurs from the regions occupied by rhizoplasts. Rhizoplasts or partial rhizoplasts lie at the flat metaphase spindle poles. By metaphase, the cell has already elongated to the extent that it is nearly twice as long as at interphase. The spindle and the cell itself elongate greatly during anaphase with a concomitant further separation of the flagellar pairs. Although the interzonal spindle persists during cytokinesis as in charophycean algae, H. angulata is similar in flagellar scale morphology and other characteristics to the chlorophycean Platymonas, which has a collapsing interzonal spindle at telophase, a phycoplast, and a wall-like theca, which develops by the fusion of small stellate scales. It is hypothesized that the collapsing telophase spindle and phycoplast evolved in green flagellates similar to Platymonas, in which cell and spindle elongation became restricted by a cell wall that evolved from stellate scales similar to those in Heteromastix. Such walled flagellates are then visualized as having eventually given rise to Chlamydomonas and to the entire range of chlorophycean algae with phycoplasts. It is pointed out that the hypothesis has a number of implications by which its validity could be judged when sufficient information becomes available.     

COMPARISONS OF NITRATE UPTAKE, STORAGE, AND REDUCTION IN MARINE DIATOMS AND FLAGELLATES

Diatoms, but not flagellates, have been shown to increase rates of nitrogen release after a shift from a low growth irradiance to a much higher experimental irradiance. We compared NO₃ ^? uptake kinetics, internal inorganic nitrogen storage, and the temperature dependence of the NO₃ ^? reduction enzymes, nitrate (NR) and nitrite reductase (NiR), in nitrogen‐replete cultures of 3 diatoms (Chaetoceros sp., Skeletonema costatum, Thalassiosira weissflogii) and 3 flagellates (Dunaliella tertiolecta, Pavlova lutheri, Prorocentrum minimum) to provide insight into the differences in nitrogen release patterns observed between these species. At NO₃ ^? concentrations <40 μmol‐N·L ^{? 1}, all the diatom species and the dinoflagellate P. minimum exhibited saturating kinetics, whereas the other flagellates, D. tertiolecta and P. lutheri, did not saturate, leading to very high estimated K _s values. Above ～60 μmol‐N·L ^{? 1}, NO₃ ^? uptake rates of all species tested continued to increase in a linear fashion. Rates of NO₃ ^? uptake at 40 μmol‐N·L ^{? 1}, normalized to cellular nitrogen, carbon, cell number, and surface area, were generally greater for diatoms than flagellates. Diatoms stored significant amounts of NO₃ ^? internally, whereas the flagellate species stored significant amounts of NH₄ ⁺ . Half‐saturation concentrations for NR and NiR were similar between all species, but diatoms had significantly lower temperature optima for NR and NiR than did the flagellates tested in most cases. Relative to calculated biosynthetic demands, diatoms were found to have greater NO₃ ^? uptake and NO₃ ^? reduction rates than flagellates. This enhanced capacity for NO₃ ^? uptake and reduction along with the lower optimum temperature for enzyme activity could explain differences in nitrogen release patterns between diatoms and flagellates after an increase in irradiance.     

Morphological evolution of silica scales in the freshwater genus Synura (Stramenopiles)

A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus, Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extant Synura species using a robust molecular analysis that included six genes, coupled with morphological characterization of the species‐specific scales. The analysis was further enriched with addition of morphological information from fossil specimens and by including the unique modern species, Synura punctulosa. We inferred the phylogenetic position of the morphologically unique S. punctulosa, to be an ancient Synura lineage related to S. splendida in the section Curtispinae. Some morphological traits, including development of a keel or a labyrinth ribbing pattern on the scale, appeared once in evolution, whereas other structures, such as a hexagonal meshwork pattern, originated independently several times over geologic time. We further uncovered numerous construction principles governing scale morphology and evolution, as follows: (i) scale roundness and pore diameter decreased during evolution; (ii) elongated scales became strengthened by a higher number of struts or ribs; (iii) as a consequence of scale biogenesis, scales with spines possessed smaller basal holes than scales with a keel and; and (iv) the keel area was proportional to scale area, indicating its potential value in strengthening the scale against breakage.     

THE ECOLOGY OF EPIPELIC ALGAE OF FIVE WELSH LAKES,WITH SPECIAL REFERENCE TO VOLVOCALEAN GREEN FLAGELLATES (CHLOROPHYCEAE)1

The ecology of epipelic algae on the marginal sediments of five Welsh lakes was studied over an annual cycle. The lakes, Llydaw, Cwellyn, Padarn, Maelog and Coron ranged from very oligotrophic to nutrient-rich. Attention was focussed on chlamydomonad flagellates, diatoms, blue-green algae and euglenoids and the different proportions of these in algae in the epipelon of lakes of contrasting water quality. A total of 75 algal taxa was found in the five lakes, 25 were species of volvocalean flagellates. Mean annual population density of these flagellates differed by an order of magnitude between the lakes. The greatest population density was recorded for Chlamydomonas anticontata Schiller in nutrient-rich Llyn Maelog. Twenty species of pennate diatoms were recorded frequently in the epipelon. In the nutrient-rich lakes, Maelog and Coron, pennate diatoms were dominant on the sediments, where they exhibited population maxima in spring and autumn. Increase in numbers of epipelic diatoms was recorded when silica concentrations were minimum in the overlying lake waters. Navicula hungarica Grun. achieved the maximum population density, 260 000 cells · cm^?2. Euglenoids formed large epipelic populations during late-summer and autumn in these nutrient-rich lakes. Blue-green algae were more important, proportionally, in the nutrient-poor mountain lakes, which had sediments of higher organic content. Chlamydomonads were the major algal component of the epipelon in the mountain lakes, Llydaw and Cwellyn, where the sediments were characterized by larger particle size, and higher organic content. In the nutrient-rich lakes, where the sediments had higher calcium content, chlamydomonads formed significant populations only during spring and summer, when nutrient levels were minimal in the overlying lakewaters.     

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.     

AN ENCYSTMENT STAGE,BEARING A NEW SCALE TYPE,OF THE ANTARCTIC PRASINOPHYTE PYRAMIMONAS GELIDICOLA AND ITS PALEOLIMNOLOGICAL AND TAXONOMIC SIGNIFICANCE1

Cysts of the Antarctic prasinophyte Pyramimonas gelidicola McFadden were found in water samples from a fjord and a saline lake in the Vestfold Hills, Antarctica Unialgal cultures of P. gelidicola from Ace Lake produced cysts. After ca. five weeks, tile cysts settled and adhered to the bottom of the culture flask. The cyst wall was covered by a scale type not seen on the flagellated cells; however, the base of the cyst scale was similar to the box scales of P. gelidicola motile cells. Cyst scales were also found off the continental shelf in Prydz Bay. In a 1.7 m sediment core taken from Ace Lake, both cyst scales and box scales of P. gelidicola occurred at most depths. Differences in the ratio of these two scale types at different depths in the core may indicate past ecological changes in the lake. Upper sediments of the core were dated at 5310 ± 90 yrs B.P., indicating that prasinophyte scales may be recognizably preserved for extended periods. P. gelidicola was widely distributed in saline lakes of the Vestfold Hills with salinities of 3.2–133% and temperatures ranging from – 5.0 to 10.4°C. This is the first report of encystment of P. gelidicola and, to our knowledge, is the first record of a prasinophyte with two distinctly different scale types occurring on cells during different stages of the life history.     

Scale Biogenesis in Synurophycean Protists: Phylogenetic Implications

The Synurophyceae is a class of golden-brown, freshwater, photosynthetic flagellates with a world-wide distribution. A well-developed taxonomy exists where genera and species are distinguished by colony or cell morphology or by the siliceous scales that cover the cells. However, phylogenetic relationships within the class are poorly understood, and incongruous taxonomic concepts occur. This study reviews scale morphology from field-collected samples and controlled culturing experiments as well as from studies of scale biogenesis. The information is used to identify homologous silicification surfaces among taxa and to document the diversity of the resulting scale structures. Thirty-two character states are coded into 11 characters in a cladistic analysis of 13 pivotal taxa. Colonial species are emphasized. One most-parsimonious phylogenetic tree is found (HI = 0, CI = 1). Synura lapponica is shown to be most closely related to Tessellaria volvocina. S. sphagnicola emerges at the base of the tree. Mallomonas caudata and the S. petersenii clade emerge from within Sectio Synura. Chrysodidymus synuroideus appears as an ancestral taxon in the Synura spinosa-like clade (i.e., Series Spinosae). The poorly understood developmental bases for some characters, especially secondary scale structures, are identified and may help focus future research.     

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 .     

ULTRASTRUCTURE OF CHRYSODIDYMUS SYNUROIDEUS (SYNUROPHYCEAE)1

A clonal isolate of Chrysodidymus synuroideus Prowse was derived form a Sphagnum bog in northern Wisconsin and maintained in culture for over 3 years. Cultured colonies consisted almost exclusively of two cells attached at the posterior, each cell bearing two unequal flagella. Correlative light and electron microscopic observations revealed that colonies composed of smaller, ovate cells represented more recent products of cell division, while colonies of elongate cells were more mature. These results support previous taxonomic conclusions, based on light microscopic observations, of field-collected specimens and body scale ultrastructure, that Chrysodidymus is a valid genus, and that two species described by Prowse on the basis of cell size differences, should be merged. In addition, ultrastructural studies of cultured Chrysodidymus demonstrated that this genus is a member of the Synurophyceae on the basis of characters related to flagellar morphology, basal body arrangement, and cytoskeletal ultrastructure. Chrysodidymus synuroideus resembles Synura sphagnicola in body scale structure, the presence of distinctive linear or clavate scales on both flagella, a relatively loose scale case, and acidophilic habital, Unlike S. sphagnicola, Chrysodidymus has no Pyrennoids, Peripheral (rather than axial) plastids, and a single posterior storage vesicle (rather than two peripheral storage vesicles).     

PROBING THE SURFACE OF LIVING DIATOMS WITH ATOMIC FORCE MICROSCOPY: THE NANOSTRUCTURE AND NANOMECHANICAL PROPERTIES OF THE MUCILAGE LAYER1

Atomic force microscopy (AFM) is used to investigate the topography and material properties of the mucilage layer of live cells of three benthic diatoms, the marine species Crasepdostauros australis E. J. Cox and Nitzschia navis‐varingica Lundholm et Moestrup and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. Contrary to previous studies, we show that this surface mucilage layer displays unique nanostructural features. In C. australis, tapping mode images revealed a soft mucilage layer encasing the silica cell wall, consisting of a smooth flat surface that was interrupted by regions with groove‐like indentations, whereas force measurements revealed the adhesive binding of polymer chains. The elastic responses of these polymer chains, as they were stretched during force measurements, were successfully fitted to the worm‐like chain model, indicating the stretching of mostly single macromolecules from which quantitative information was extracted. In P. viridis, tapping mode images of cells revealed a mucilage layer that had the appearance of densely packed spheres, whereas force measurements exhibited no adhesion. In N. navis‐varingica, tapping mode images of the outer surface of this cell in the girdle region revealed the absence of a mucilage layer, in contrast to the other two species. In addition to these topographic and adhesion studies, the first quantitative measurement of the elastic properties of microalgal extracellular polymeric substance is presented and reveals significant spatial variation in the C. australis and P. viridis mucilage layers. This study highlights the capacity of AFM in elucidating the topography and mechanical properties of hydrated microalgal extracellular polymeric substance on a nanoscale.     

Mineralized scale patterns on the cell periphery of the chrysophyte Mallomonas determined by comparative 3D Cryo-FIB SEM data processing

Unicellular protists can biomineralize spatially complex and functional shells. A typical cell of the photosynthetic synurophyte Mallomonas is covered by about 60–100 silica scales. Their geometric arrangement, the so-called scale case, mainly depends on the species and on the cell cycle. In this study, the scale case of the synurophyte Mallomonas was preserved in aqueous suspension using high-pressure freezing (HPF). From this specimen, a three-dimensional (3D) data set spanning a volume of about 25.6 μm × 19.2 μm × 4.2 μm with a voxel size of 12.5 nm × 12.5 nm × 25.0 nm was collected by Cryo-FIB SEM in 3 h and 24 min. SEM imaging using In-lens SE detection allowed to clearly differentiate between mineralized, curved scales of less than 0.2 μm thickness and organic cellular ultrastructure or vitrified ice. The three-dimensional spatial orientations and shapes of a minimum set of scales (N = 13) were identified by visual inspection, and manually segmented. Manual and automated segmentation approaches were comparatively applied to one arbitrarily selected reference scale using the differences in grey level between scales and other constituents. Computational automated routines and principal component analysis of the experimentally extracted data created a realistic mathematical model based on the Fibonacci pattern theory. A complete in silico scale case of Mallomonas was reconstructed showing an optimized scale coverage on the cell surface, similarly as it was observed experimentally. The minimum time requirements from harvesting the living cells to the final scale case determination by Cryo-FIB SEM and computational image processing are discussed.     

LIGHT MICROSCOPY AND ELECTRON MICROSCOPY OF NEPHROSELMIS SPINOSA SP. NOV. (PRASINOPHYCEAE,CHLOROPHYTA)1

Nephroselmis spinosa Suda sp. nov. is described based on LM and EM observations. Two strains of N. spinosa (S222 and SD959‐3) were isolated from sand samples collected from the northwest coast of western Australia. The cells were remarkably right–left flattened and appeared ellipse or bean‐shaped when viewed from their right or left side. A single, parietal, crescent chloroplast was pale green to yellowish green and contained one conspicuous eyespot in its anterior ventral edge near the base of the short flagellum. A pyrenoid with three starch plates was located at the dorsal of the chloroplast. The cells divided by transverse binary cell division, as is common in other species of this genus. This alga possessed four types of body scales, and three scale types were similar to N. olivacea Stein and N. astigmatica Inouye & Pienaar. However, the fourth and outermost scale type was distinctive because although it was a spiny stellate scale with nine spines, one of them extended about 1 μm and was slightly curved with a hook at the end. This scale morphology, an important taxonomic characteristic, has never been described for the genus Nephroselmis. The cell's morphology, pyrenoid structure, hair scales, and cell size were distinctive from previously described Nephroselmis species, and its unique scale characteristic led me to name this newly proposed species “spinosa,” meaning spiny.     

High molecular mass glycoproteins associated with the siliceous scales and bristles of Mallomonas splendens (Synurophyceae) may be involved in cell surface development and maintenance

The elaborate scale case of Mallomonas splendens (Synurophyceae) consists of an overlapping arrangement of siliceous scales. In addition, siliceous bristles are attached to specialized base plate scales located at both the anterior and posterior ends of the cells. We have generated monoclonal antibodies against molecules associated with the scale case of M. splendens. One of these antibodies, designated MsS.H9, labelled a proteinaceous epitope of high-molecular-mass cell surface glycoproteins. Immunofluorescence and immunoelectron microscopy demonstrated that only two regions of M. splendens scale cases were labelled by MsS.H9, namely, the upper surface of the scales that contact neighboring scales and the bases of the bristles. Immunoelectron microscopy using thin sections of M. splendens cells showed these labelling sites corresponded to the amorphous material at the sites of scale-to-scale overlap and to a fibrillar complex located at scale-to-bristle attachment sites. Scales and bristles of M. splendens are formed within the cell, in silica deposition vesicles. Immunolabelling of cell sections containing developing scales and bristles showed that MsS.H9 labelling sites were present very early in the formation of these cell surface components. MsS.H9 labelling was also found associated with developing flagellar hairs whereas no labelling was detected on these structures after their deployment onto the flagellum. The location of MsS.H9 labelling sites strongly suggests that the molecule(s) recognized by the antibody plays a role in the adhesion of the individual components making up the scale case of M. splendens.Abbreviations CER chloroplast endoplasmic reticulum - ER endoplasmic reticulum - SDV silica deposition vesicle This work was supported by a grant from the Australian Research Council to R.W. We thank Dr. P. L. Beech for Fig. 13, Dr. L. Perasso for technical assistance and the Plant Cell Biology Group for the use of their monoclonal facilities.     

Multigene phylogeny of Synura (Synurophyceae) and descriptions of four new species based on morphological and DNA evidence

We used phylogenetic analyses based on multiple gene sequences (partial nr SSU and LSU rDNA, partial pt LSU rDNA, psaA and rbcL) from 148 strains (including three outgroups) and scale ultrastructure to examine phylogenetic relationships among species of the colonial genera Synura and Tessellaria. The phylogenetic tree based on the combined dataset was congruent with ultrastructural characteristics of the scales. Synura was divided into three major clades, two including species in section Synura, and one representing section Peterseniae. One clade, consisting of seven strains of S. uvella (section Synura), diverged at the base of the genus. The second clade consisted of the remaining species belonging to the section Synura. The third clade, containing organisms in the section Peterseniae and characterized by scales possessing a keel, was monophyletic with strong support values. Based on our findings, S. uvella needs to be in a separate section from other spine-bearing species, and we therefore propose new sectional ranks; Synura, Peterseniae, Curtispinae (presence of body scales with slender spines, tubular scales and caudal scales). We further propose four new species based on phylogenetic analyses and unique scale characters: S. longitubularis sp. nov., S. sungminbooi sp. nov., S. soroconopea sp. nov. and S. lanceolata sp. nov. Lastly, we propose a new genus name, Neotessella, to replace the invalid use of the name Tessellaria.     

AUXOSPORE FORMATION AND THE MORPHOLOGY OF THE INITIAL CELL OF THE MARINE ARAPHID DIATOM GEPHYRIA MEDIA (BACILLARIOPHYCEAE)1

Recent studies have led to a rapid increase in knowledge of auxospore formation in diatoms. However, these studies have been limited to centric and raphid pennate diatoms, and there is still very little information for the araphid pennate diatoms. Using LM and SEM, we studied the development of the auxospore and the initial cell of the marine epiphytic diatom Gephyria media Arnott. Auxospores were bipolar and curved in side view, as in many other pennate diatoms. SEM revealed many transverse perizonial bands, all of which were incomplete rings. There was an elongate, sprawling, silicified structure beneath the ventral suture of the transverse perizonial bands. This structure is presumably equivalent to the longitudinal perizonial band in other pennate diatoms, although we could not determine the homologous relationship between the two features. Scales were found both in the inner wall of the perizonium and around the primary perizonial bands. The presence or absence of scales may be of phylogenetic significance in diatoms, only during the final stages of auxospore formation because scales are found in early spherical stages. The distinctive finger‐like structures observed throughout all stage of G. media have not been observed before in the other diatom taxa.