AMPHIESMAL ULTRASTRUCTURE OF DINOFLAGELLATES: A REEVALUATION OF PELLICLE FORMATION1

The ultrastructure of the amphiesma during pellicle formation was investigated in two species of Dinophyceae, Amphidinium rhynchocephalum Anissimowa and Heterocapsa niei (Loeblich) Morrill & Loeblich using thin sections. In both species the amphiesma consists of an outermost membrane (i.e. the plasma membrane) underlain by amphiesmal vesicles. In A. rhynchocephalum the latter appear empty whereas each amphiesmal vesicle in H. niei contains a thecal plate and a thin, amorphous layer (dark-staining layer) located between, the thecal plate and the inner amphiesmal vesicle membrane. When cells of both taxa are carefully fixed, amphiesmal vesicles are always separate entities (i.e. the sutures are undisrupted). During ecdysis the following amphiesmal components are shed: the plasma membrane, the outer amphiesmal vesicle membrane, and in H. niei the thecal plates. The inner membranes of the amphiesmal vesicles then fuse with each other and form a continuous membrane (termed pellicle membrane) that remains tightly oppressed to an underlying amorphous layer (pellicular layer). In A. rhynchocephalum the pellicular layer is already present in vegetative non-ecdysed cells, whereas in H. niei it forms during ecdysis beneath the pellicle membrane. During ecdysis in H. niei, material from the dark-staining layer precipitates on the outer surface of the pellicle membrane, where it forms a characteristic honeycomb pattern. The new observations are incorporated into a revised model of pellicle formation in dinoflagellates and contrasted with earlier proposals.     

MICROMORPHOLOGY OF A SMALL DINOFLAGELLATE PROROCENTRUM MARIAE-LEBOURIAE (PARKE & BALLATINE) COMB. NOV.1,2,3

The surface structures of the bivalvate dinoflagellate Prorocentrum mariae-lebouriae are described in detail. It has an almost spheroidal shape in face-view, a compressed saucer-shape in side view, with a distinct striated band at the edge of the cell. Its surface is covered with small spines in a regular pattern, with 450 nm distance between pairs. The spines are 100–120 nm wide and 200–300 nm long. There are 600–700 spines on each valve. At the anterior cell end, one of the values has a V-shaped depression which contains a specialized structure accommodating the 2 flagellar pores. The flagellar pores are-enclosed by 8 small, thick plates held together and to the values by sutures. The flagellar pore area consists of 2 distinct structures: an apical collar possessing a curved forked plate and a larger structure composed of an unbranched, plate. There are 2 flagellar canals located between the flagellar pore plates. Beneath each flagellar canal lies a row of 11 microtubules. A row of microtubules forming a microtubular cylinder is situated adjacent to the oblong flagellar canal near a simple pusule. The microtubular cylinder encircles electron dense bodies. The bases of the longitudinal and transverse flagella appear to lie at an angle to each other. The above features are illustrated with transmission and scanning electron micrographs.     

Ecdysis and the location of the plasma membrane in the dinoflagellateHeterocapsa niei

Summary The outer membrane is the plasma membrane in the pelliculate dinoflagellateHeterocapsa niei (Loeblich) Morrill and Loeblich, except when the cell is preparing to ecdyse and is forming a new amphiesma. At maturity the theca and pellicle are enclosed within a single large amphiesmal vesicle which surrounds the cell; thus, the amphiesmal components are intracellular. The plasma membrane lies outside this vesicle and is continuous with the flagellar membrane. At ecdysis retraction of the flagella and fusion of the innermost or cytoplasmic membrane over the flagellar region facilitates the shedding of all layers external to the cytoplasmic membrane. This membrane eventually becomes the bounding membrane (plasma membrane) of the reformed amphiesma.     

THREE NEW BENTHIC SPECIES OF PROROCENTRUM (DINOPHYCEAE) FROM CARRIE BOW CAY,BELIZE: P. SABULOSUM SP. NOV., P. SCULPTILE SP. NOV., AND P. ARENARIUM SP. NOV.1

Three new benthic, sand-dwelling dinqflagellate species, Prorocentrum sabulosum, Prorocentrum scuptile, and Prorocentrum arenarium, from coral rubble are described from scanning electron micrographs. Species were identified based on shape, size, surface micromorphology, ornamentation of thecal plates, and architecture of the periflagellar area and intercalary band. Cells of P. sabulosum are oval with a cell size of 48–50 μm long and 41–48 μm wide. The areolae are round to oval and numerous (332–450 per valve) and range from 1 to 1.6 μm in size. The periflagellar area of P. sabulosum bears a wide V-shaped depression with a flat ridge and lacks ornamentation; it accommodates six pores: one large flagellar pore, an adjacent smaller auxiliary pore, and four pores of unknown function. The flagellar and auxiliary pores are surrounded by a narrow apical collar. The intercalary band of P. sabulosum is smooth. Prorocentrum sculptile cells are broadly oval, 32–37 nm long, and 30–32 μm wide in valve view with a deep-sculptured apical area. The valves are smooth and are marked with shallow depressions (856–975 per valve). Some of these depressions have a small round opening (0.13 μm in diameter). The periflagellar area is V-shaped with a deeply indented depression; it accommodates the two flagella and a thin angled apical plate. The intercalary band is smooth. Prorocentrum arenarium cells are nearly round in valve view 30–32 μm in diameter. Thecal surface is smooth with scattered kidney-shaped valve poroids (65–73 per valve) and marginal poroids (50–57 per valve). Length and width of poroids are 0.62 μm and 0.36 μm, respectively. The periflagellar area is an unornamented, broad triangle into which a large flagellar pore and a smaller auxiliary pore are fitted. Both flagella, longitudinal and transverse, protrude from the flagellar pore. The intercalary band is smooth. The presence of a peduncle-like structure (2–3 μm long) in P. arenarium was observed situated in the flagellar pore.     

MALE GAMETES OF ATRACTOMORPHA ECHINATA HOFFMAN (CHLOROPHYCEAE)1

Many naked gametes are produced in each fusiform, male gametangium of Atractomorpha echinata Hoffman and are liberated through irregularly shaped pores in the gametangial wall. They are typically biflagellate, pyriform or fusiform in shape, 6-11 μm long, and only a few micrometers wide. A mature male gamete is characterized by: (i) a nucleus with condensed chromatin and no nucleoli, (ii) a reduced, starch filled chloroplast occupying a posterior position, and (iii) a cup shaped eyespot consisting of a single layer of plastoglobuli. The flagellar apparatus includes two types of flagellar roots alternating in a cruciate pattern. One type consists of two microtubules, while the other consists of microtubules of varying number, usually eight or nine, but rarely as many as eleven. The paired basal bodies are connected anteriorly by a broad, striated distal fiber; there is no dense apical cap as reported in Sphaeroplea sperm. A unique structure, consisting of three layers of small subunits (6–8 nm diameter) arranged in a paracrystalline array, is positioned beneath each basal body. Based on the structure of its male gametes, Atractomorpha clearly demonstrates affinity with the chlorophycean rather than the ulvaphycean line of evolution. Moreover, if phylogenetic affinities for the Sphaeropleaceae are to be sought among other groups of green algae, the Chlorococcales appears the most promising candidate.     

THE FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF CARTERIA1,2

The fine structure of the flagellar apparatus of 5 species of the green quadriflagellate alga Carteria is described. The 5 species can be morphologically separated into 2 groups on the bases of cell shape and ultrastructure of the pyrenoid and flagellar apparatus. Group I cells are spherical, possess many pyrenoid thylakoids, and retain a flagellar apparatus similar to that of Chlamydomonas reinhardi. The flagellar bases are oriented at approximately 90° to one another, have distal and proximal fibers, and are associated with 4 cruciately arranged microtubule bands. Cells of group II are ellipsoid, possess few pyrenoid thylakoids, and show a complex system of microtubule bands and sigmoid-shaped, electron dense rods which extend between opposite pairs of basal bodies. The basal bodies of group II cells are directed inward in a circular pattern rather than outward as in group I cells. Unlike Chlamydomonas, the distal fiber of the Carteria species is nonstriated. The proximal fiber is striated, and both distal and proximal fibers are composed of 60–80 Å diameter microfibrils.     

GENERAL ULTRASTRUCTURE AND FLAGELLAR APPARATUS ARCHITECTURE OF WOLOSZYNSKIA LIMNETICA (DINOPHYCEAE)

The ultrastructure of Woloszynskia limnetica Bursa was examined using serial thin section electron microscopy. Sections of W. limnetica reveal numerous chloroplast profiles without any obvious pyrenoids. The extensive pusular complex consists of a "smooth" part and a part lined with electron-dense particles. The nucleus is located in the episome. A stigma (= eyespot) consisting of numerous electron-dense globules is situated beneath the amphiesmal vesicles of the sulcal groove. The longitudinal microtu-bular root extends between the stigma and the amphiesma vesicles. Subthecal fibers occur in conjunction with the microtubules and the stigma. Both flagellar exit apertures are encircled by a broad striated collar, each giving rise to a fiber that extends along the pusular canal opening. The striated collars are interconnected by the ventral ridge fiber. The basal part of the transverse flagellum has, in addition to the normal paraxonemal rod (= striated strand or fiber), a semicircular structure consisting of fibrils. The flagellar apparatus is complex but possesses components typically found in the Dinophyceae. The longitudinal mi-crotubular root is broad and is connected to both striated collars. The transverse basal body gives rise to the transverse microtubular root, which in turn is associated with microtubules that extend to the interior of the cell and with the transverse striated root. The transitional region of both basal bodies possesses a distinctive fibrous ring attached to each microtubular triplet by short fibers that collectively appear as spokes of a wheel. Not unexpectedly, the flagellar apparatus of Woloszynskia limnetica is much like that of the related Woloszynskia sp.; however, some dif ferences were discovered. A phylogenetic relationship between Woloszynskia limnetica, W. coronata ( Wolosz.) Thompson, and W. sp. is indicated based on similarities in pusule and stigma structure .     

COMPARATIVE ANALYSES OF THE DINOFLAGELLATE FLAGELLAR APPARATUS. I. WOLOSZYNSKIA SP.1

The three-dimensional structure of the flagellar apparatus in Woloszynskia sp. was determined. This recently discovered dinoflagellate possesses two basal bodies that are offset from one another and lie at an angle of approximately 110°. The transverse basal body is associated with a striated fibrous root assemblage that consists of two differently staining fibrous portions with identical striation periodicity. Unlike the transverse striated fibrous roots reported in other dinoflagellates, this assemblage extends to the cell's right beyond the proximal end of the transverse basal body. The striated fibrous root complex is attached to the anterior end of the longitudinal microtubular root by a broad striated fibrous connective. The longitudinal basal body is also associated with the longitudinal microtubular root. The flagellar opening of each emerging axoneme is surrounded by a striated collar. The striated collars are linked to one another by a striated fibrous, striated collar connective. The variations and similarities of the flagellar apparatus and the ventral ridge/striated collar connective in Woloszynskia sp. are compared to similar components in other dinoflagellates.     

THE FLAGELLAR APPARATUS OF GYMNODINIUM SP. (DINOPHYCEAE)1

The detailed structure of the flagellar apparatus has been determined in a small dinoflagellate of the genus Gymnodinium. Although diminutive, this dinoflagellate possesses a complex flagellar apparatus consisting of a posteriorly directed microtubular root, a transverse striated fibrous root, several striated fibrous connectives that attach the basal bodies to one another as well as to the different roots, and a conspicuous non-striated fibrous connective that directly links the posteriorly directded microtubular root with the extended lobe of the nucleus. This represents the second discovery of a nuclear connective linked to the flagellar apparatus in the Dinophyceae but is the first report to elucidate the spatial relationships of the connective with the flagellar apparatus and the cell. A detailed diagrammatic reconstruction is provided and the similarities between these flagellar apparatus features are compared with those known for other dinoflagellates. Additionally, the structure and displacement of the nuclear connective are compared with nuclear connectives described in other protists.     

COMPARATIVE ULTRASTRUCTURE OF ZOOSPORES WITH PARALLEL BASAL BODIES FROM THE GREEN ALGAE DICTYOCHLORIS FRAGRANS AND BRACTEACOCCUS SP.

The chlorococcalean algae Dictyochloris fragrans and Bracteacoccus sp. produce naked zoospores with two unequal flagella and parallel basal bodies. Ultrastructural features of the flagellar apparatus of these zoospores are basically identical and include a banded distal fiber, two proximal fibers, and four cruciately arranged microtubular rootlets with only one microtubule in each dexter rootlet. In D. fragrans, each proximal fiber is composed of two subfibers, one striated and one nonstriated, and each sinister rootlet is composed of five microtubules (4/1), decreasing to four away from the basal bodies. In Bracteacoccus sp., each proximal fiber is a single unit, the sinister rootlets are four (3/1) or rarely five (4/1) microtubules, and each basal body is associated with an unusual curved structure. The basic features of the flagellar apparatus of the zoospores of these two algae resemble those of Heterochlamydomonas rather than most other chlorococcalean algae that have equal length flagella, basal bodies in the V-shape arrangement, and clockwise absolute orientation. It is proposed that these algae with unequal flagella and parallel basal bodies have a shared common ancestry within the green algae.     

THE FLAGELLAR APPARATUS OF OXYRRHIS MARINA (PYRROPHYTA)1

The three-dimensional structure of the flagellar apparatus in the dinoflagellate Oxyrrhis marina has been reinvestigated and found to consist of several previously unknown components and component combinations that appear strikingly similar to those of some gymnodinoid taxa. The flagellar apparatus of this dinoflagellate is asymmetric and extremely complex consisting of a longitudinal and a transverse basal body that gives rise to eight structurally different components. The only posteriorly directed component is the large microtubular root that consists of 45–50 microtubules at its origin and is attached proximally to a perpendicularly oriented striated fibrous component. Arising from each basal body, two striated fibrous roots with different periodicities extend to the cell's left. A single stranded microtubular root with associated electron dense material emanates from the transverse basal body and also extends to the cell's left. A striated fibrous connective arises from the longitudinal basal body and extends toward the cell's right ventral surface and terminates near the sub-thecal microtubular system. A compound root consisting of microtubules and electron dense material also originates from the longitudinal basal body and extends ventrally into the anterior region of the tentacle. Structural similarities between the parallel striated fibrous roots of Oxyrrhis and Polykrikos are discussed as are flagellar apparatus similarities among other gymnodinoid dinoflagellates. A diagrammatic reconstruction of the Oxyrrhis flagellar apparatus is also presented.     

ULTRASTRUCTURE OF THE FLAGELLAR APPARATUS OF PYROBOTRYS (CHLOROPHYCEAE)1

The flagellar apparatus of Pyrobotrys has a number of features that are typical of the Chlorophyceae, but others that are unusual for this class. The two flagella are inserted at the apex, but they extend to the side of the cell toward the outside of the colony, here designated as the ventral side. Four basal bodies are present, two of which extend into flagella. Four microtubular rootlets alternate between the functional and accessory basal bodies. In each cell, the two ventral rootlets are nearly parallel, but the dorsal rootlets are more widely divergent. The rootlets alternate between two and four microtubules each. A striated distal fiber connects the two functional basal bodies in the plane of the flagella. Two additional, apparently nonstriated, fibers connect the basal bodies proximal to the distal fiber. Another striated fiber is associated with each four-membered rootlet near its insertion into the flagellar apparatus. A fine periodic component is associated with each two-membered rootlet. A rhizoplast-like structure extends into the cell from each of the functional basal bodies. The arrangement of these components does not reflect the 180° rotational symmetry that is usually present in the Chlorophyceae, but appears to be derived from a more symmetrical ancestor. It is suggested that the form of the flagellar apparatus is associated with the unusual colony structure of Pyrobotrys.     

A STUDY OF THE SPERMATOZOIDS OF DICHOTOMOSIPHON TUBEROSUS (CHLOROPHYCEAE)1

Spermatozoids of the siphonous green alga Dichotomosiphon tuberosus (A. Br.) Ernst are specialized gametes which differ in many respects from other green algal motile cells, but whose microanatomy nevertheless indicates its chlorophycean affinities. Each cell is anteriorly biflagellate and contains an irregularly shaped nucleus attached to the flagellar bases by a complex support apparatus. There is a single reduced chloroplast in each spermatozoid and numerous (50–100) minute spherical mitochondria, only 0.3 μm diam. These move vigorously in the living cell and when viewed with the light microscope they bear a striking resemblance to bacteria. Rather unexpectedly, no contractile vacuoles could be detected, even though the gametes are naked freshwater cells. Daring spermatogenesis the nucleoli of the vegetative cells disperse and are replaced by a large dense body presumably formed from either nucleolar material or condensed chromatin. The flagellar apparatus includes a cruciate flagellar root system, a feature now known to be characteristic of most green algae, exceptions being those putative ancestors of the higher plants and bryophytes. Discharge of spermatozoids from the antheridia is extremely rapid and the whole process may be finished in 30 sec. The antheridium lacks a pore apparatus, but at maturity bursts open explosively at the apex. Phyletic affinities are discussed and it is concluded that the ultrastructure of the motile cells does not, at this time, support the separation of the siphonous green algae from other green algae into a separate class.     

POLYPHYLETIC ORIGIN OF PARALLEL BASAL BODIES IN SWIMMING CELLS OF CHLOROPHYCEAN GREEN ALGAE (CHLOROPHYTA)1

The evolutionary affinities of Heterochlamydomonas Cox and Deason and Dictyochloris Vischer ex Starr were investigated using phylogenetic analyses of a combined data set of 18S and 28S rDNA sequences with those from 38 additional green algae. Previous ultrastructural studies have shown that motile cells of Heterochlamydomonas and Dictyochloris have an unusual flagellar apparatus organization in that the two flagella are of unequal length and the basal bodies are persistently parallel. Because of this similarity these taxa, along with Bracteacoccus Tereg, a third taxon with this same flagellar apparatus arrangement, are hypothesized to be closely related. We show, with maximum parsimony and Bayesian analyses, that the parallel basal bodies are not homologous in the three genera. Rather, Heterochlamydomonas is most closely related to Chlamydomonas baca in the clockwise flagellar apparatus clade, and Dictyochloris and Bracteacoccus are nested within the Sphaeropleales, which has the directly opposite flagellar absolute orientation. Surprisingly, Dictyochloris and Bracteacoccus are not supported as closest relatives. These relationships are supported by morphological features such as the presence or absence of a walled motile cell but not by the orientation of the basal bodies. In addition, our data are derived from multiple isolates of each study genera, and the analyses show that Heterochlamydomonas and Dictyochloris are each monophyletic.     

Dinophyte chloroplasts and phylogeny - A review

Dinophytes acquired chloroplasts obviously early in evolution and later lost them multiple times. Most families and genera contain both photosynthetic and heterotrophic species. Chloroplasts enveloped by three membranes with thylakoids in stacks of three, containing peridinin as the main pigment, are regarded as the original dinophyte plastids. Pyrenoids are generally present. Stigmata, if present, are usually parts of the chloroplast or are modified original plastids. The form II type RUBISCO found in the dinophytes is unique for eukaryotes, otherwise known only in some anaerobic bacteria. It is disputed whether the original dinophyte chloroplasts are derived from a prokaryotic or an eukaryotic endosymbiosis. Various dinoflagellates contain aberrant chloroplasts. Glenodinium foliaceum and Peridinium balticum have a single complete endosymbiont, originally a pcnnate diatom. Podolampas bipes houses several dictyophycean symbiont cells. The “symbionts” of Lepidodiniurn viride and Gymnodinium chlorophorum are highly reduced prasinophyte cells. The chloroplasts of Gymnodinium mikimotoi have aberrant pigments (fucoxanthin derivatives, no peridinin) and fine structure. The dinoflagellate hosts do not seem to contain any parts of the former endosymbiont except the chloroplasts. Photosynthetic Dinophysis species have cryptophycean-like chloroplasts, whereas symbiotic cyanobacteria are found in other members of the Dinophysiales, e.g., Ornithocercus. Various dinophytes, e.g. Gymnodinium aeruginosum, use kleptochloroplasts from ingested cryptophytes transiently for photosynthesis. Original or secondarily acquired chloroplasts can only be used for phylogenetic considerations in exceptionally cases: it seems unlikely that the Prorocentrales have evolved from the Dinophysiales because all Prorocentrales possess original dinoflagellate chloroplasts, whereas no member of the Dinophysiales has such chloroplasts.     

COMPARATIVE ANALYSIS OF THE DINOFLAGELLATE FLAGELLAR APPARATUS IV. GYMNODINIUM ACIDOTUM1

Gymnodinium acidotum Nygaard is a freshwater dinoflagellate that is known to harbor a cryptomonad endosymbiont whose chloroplasls give the organism an overall blue-green color. The ultrastructure of G. acidotum was examined with particular attention being given to the three dimensional nature of the flagellar apparatus. The fiagellar apparatus is composed of two functional basal bodies that are slightly offset and lie at an angle of approximately 90° to one another. As in other dinoflagellates the transverse basal body is associated with a striated, fibrous root that extends from the proximal end of the basal body to the transverse flagellar opening. At least one microtubular root extends from the proximal end of the transverse basal body, and a multi-membered longitudinal microtubular root is associated with the longitudinal basal body. The most striking feature of the flagellar apparatus of G. acidotum is the large fibrous connective that extends from the region of the proximal ends of the basal bodies to the cingulum on the dorsal side of the cell. A similar structure has been reported from only one other dinoflagellate, Amphidinium cryophilum Wedemayer, Wilcox, and Graham. The presence of this structure as well as similarities in external morphology suggest thai these two species may be more closely related to each other than either is to other gymnodinioid taxa. The taxonomic importance of dinoflagellate flagellar apparatus components is discussed.     

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.     

Biecheleria tirezensis sp. nov. (Dinophyceae,Suessiales), a new halotolerant dinoflagellate species isolated from the athalassohaline Tirez natural pond in Spain

A new euryhaline and eurythermal dinoflagellate species, Biecheleria tirezensis sp. nov., is described based on samples taken from an extreme environment, the athalassohaline and particularly sulphate-rich Tirez natural pond (Spain). This species is able to survive in salinities from almost fresh water up to 56 and over a 5–25°C temperature range. Thus, the ecological characteristics of this isolate differentiate it from other species of the same genus. Its morphology, as examined by light, scanning and transmission electron microscopy, shows that the cells are almost spherical, with several series of amphiesmal vesicles. It also has a single elongate amphiesmal vesicle (EAV) observed by SEM and the eyespot has a type E structure, typical of Biecheleria. Spherical and smooth cysts were observed in old cultures. The pigment composition is typical of a peridinin-containing dinoflagellate. Phylogeny inferred from nuclear rDNA SSU, ITS and LSU sequences showed the isolate belongs to the genus Biecheleria, closest to B. cincta and B. brevisulcata. Modelling and analysis of the secondary structure of its ITS2 region, and that of other species of the same genus and some representatives of the most closely related genera, indicated that the isolate represents a new species clearly separated from but related to B. cincta. The criterion of the presence of Compensatory Base Changes (CBCs) in the secondary structure of the ITS2 region as an indicator of species differentiation confirmed this, supporting the establishment of the Tirez pond isolate as a new species of Biecheleria.     

A new model for the structure of the centriolar satellite complex in spermatozoa

The ultrastructure of the centriolar satellite complex in the spermatozoon of the hydroid, Pennaria, is presented. The complex consists of nine spoke-like arms which emanate from the distal centriole and of nine wedgeshaped connectives which extend into the flagellum joining each of the alpha doublets and the flagellar plasmalemma. Based upon these observations a new model for the structure of the centriolar satellite complex is proposed. In addition, similar centriolar satellite complexes are reported in the spermatozoa of two echinoderms, Ctenodiscus crispatus and Thyone briareus, in support of the proposed model.