Raphid Valve Research Articles

Freshwater Cocconeis species (Bacillariophyceae) from Southeastern Brazil, and description of C. amerieuglypta sp. nov.

ABSTRACTCocconeis Ehrenberg is a monoraphid diatom genus included in the Family Cocconeidaceae. It occurs in marine and freshwater environments, living attached to a substrate by the raphid valve. Through the documentation of the taxa found in LM and SEM analyses, this study aims to increase the knowledge about freshwater Cocconeis species occurring in Brazilian waters. In addition, one new species is formally described here. Seven samples were chosen from a total of 346 samples investigated for monoraphid diatoms in São Paulo state, Brazil, due to their representativeness for Cocconeis biodiversity. These samples include periphytic, metaphytic and surface sediment materials. One sample from Ivory Coast was also analysed to compare a similar taxon with the taxa found. The biodiversity and the occurrence of the genus Cocconeis were low in our study material (nine taxa) despite the great amount of samples analysed for monoraphid taxa. Nevertheless, one taxon was considered a new species, being described here. Finally, this study was based on morphological characters of the frustule observed in LM and SEM analysis, showing the importance of both to better understand the variability of each species and to separate similar taxa.

Оn taxonomic position of two species of achnanthoid diatoms (Achnanthidiaceae, Bacillariophyceae)

Results of light and scanning electron microscopy investigations of valves of two freshwater achnanthoid diatoms are provided. Based on the structure of external terminal raphe endings, represented by simple pores, and cocconeoid habitus Achnanthes joursacensis Hérib. is transferred to the genus Platessa. Achnanthes rostellata A. Cleve is transferred to the genus Lemnicola due to presence of stauros on raphid valve and external terminal raphe fissures curved in opposite directions.

<p align="left">Cocconeis tortilis: a new marine diatom (Bacillariophyta, Cocconeidaceae) from Japan

A new species of Cocconeis, C. tortilis, was found on some seaweed collected from the Izu and Okinawa Islands of Japan. Its morphology was examined using both light and electron microscopy; details are described herein. This small diatom is characterized by: 1) a concave raphid valve with a straight raphe inclined from the apical axis, central area forming stauros, and uniseriate striae consisting of circular areolae occluded by hymens: 2) a twisted convex araphid valve with a narrow lanceolate sternum inclined from the apical axis, and uniseriate striae consisting of several loculate areolae occluded by hymens: and 3) a cingulum consisting of three non fimbriated girdle bands including a valvocopula.

<p class="HeadingRunIn"><strong><em>Cocconeis</em> <em>churalis</em>: a new marine diatom (Bacillariophyta, Cocconeidaceae) from Japan</strong></p>

A new species of Cocconeis, C. churalis, was found on a red seaweed collected from the Southwest Islands of Japan. Its morphology was examined with both light and scanning electron microscopy and the details are described here. This small diatom is characterized by the concave raphid valve with a slightly sigmoid raphe and uniseriate striae consists of circular areolae occluded by hymenes with perforations arranged in centric array type, the convex araphid valve with uniseriate striae consists of several alveoli occluded hymenes with perforations arranged in a parallel array type, and the cingulum consists of four non-fimbriated girdle bands including a valvocopula.

A NEW MARINE MONORAPHID SPECIES, ACHNANTHES PSEUDOLONGIPES SP. NOV., FROM MIYAGI, JAPAN

A new monoraphid marine species, Achnanthes pseudolongipes, is described. The structure of its valves and girdle resemble those of A. longipes Agardh, as well as the shape of the plastid. However, A. longipes has biseriate striae on both valves, whereas A. pseudolongipes has uniseriate striae on the raphid valve and biseriate (or triseriate) on the araphid valve. In the genus Achnanthes sensu stricto, only A. pseudolongipes possesses both uniseriate and biseriate striae. The number of striae between costae is one of the most effective features of the valve for the identification of taxa in the genus Achnanthes sensu stricto.

LEMNICOLA HUNGARICA (GRUNOW) ROUND & BASSON FROM SOUTHERN BRAZIL: ULTRA-STRUCTURE, PLASTID MORPHOLOGY AND ECOLOGY

Lemnicola hungarica (Grunow) Round & Basson taken from brackish and freshwater environments in Southern Brazil was studied for its ultra-structure details, plastid morphology, and ecology. Previously undescribed details are given: a ring of elongated areolae on the mantle of L. hungarica and its plate-like plastid that lies on the araphid valve where it reaches the valve margin and curves itself towards the raphid valve. Lemnicola hungarica thrives in truly freshwater conditions where conductivity values are below 300 μS/cm, and where floating plants are also present.

Fine-structure of the vegetative frustule, perizonium and initial valve of Achnanthes yaquinensis (Bacillariophyta)

This study clarifies the fine structure of the vegetative and initial valves of Achnanthes yaquinensis and briefly compares them to other Achnanthes species. It also elucidates the structure of the perizonium, based on auxospore development in short-term cultures. The araphid valve has marginal ridges and terminal spines that allow connecting valves to form a chain. The terminal spines develop from the rapheless sternum. The complete cingulum consists of 3–5 split bands with two rows of areolae. These features can be used to discriminate species within the genus. Sexual reproduction is isogamous with two mother cells producing two auxospores, which are enclosed in mucilage. The perizonium develops on one side of an auxospore only, comprising one large central longitudinal band and four closed bands. There are no transverse perizonial bands. The raphid valve of the initial cell forms first, underneath the longitudinal perizonium, followed by the araphid valve, which is not covered by any perizonial bands. The araphid valve of the initial cells lacks a marginal spine, and the rapheless sternum lies more centrally than in the vegetative cell. The relationship of the genus Achnanthes to other monoraphid diatoms is discussed briefly.

Morphology and taxonomy of Amphicocconeis gen. nov. (Achnanthales, Bacillariophyceae, Bacillariophyta) with considerations on its relationship to other monoraphid diatom genera

SEM and TEM observations on the cleaned material used by Hustedt for the preparation of the type of the marine diatom Cocconeis disculoides Hustedt and on living specimens of the species scraped from Posidonia oceanica (L.) Delile leaves collected in different coastal areas of the Mediterranean Sea revealed structures that differentiate this species from the genus Cocconeis Ehrenberg. The external apical raphe endings have marked terminal fissures; valvocopulae extend over a large part, or all, of the valve surface and bear rounded perforations arranged differently in the two bands; areolae are occluded by simple hymenes with irregularly distributed, rounded perforations. Recently, C. disculoides Hustedt was transferred to Psammococconeis Garcia, a new genus found in sediment samples from Port Belo Peninsula (Brazil), as P. disculoides (Hustedt) Garcia. However, the genus Psammococconeis lacks the raphe terminal fissures, shows two types of areolae in the sternum valve mantle and an extended valvocopula with perforations only in the raphid valve. Furthermore, in P. disculoides, the areolae are occluded by fimbriate hymenes in both valves. These observations lead us to propose the new genus Amphicocconeis, which at present includes only A. disculoides (Hustedt) comb. nov. The elements of Hustedt's type material examined by Garcia should be the lectotype of a new species of Psammococconeis.

PSAMMOCOCCONEIS, A NEW GENUS OF BACILLARIOPHYTA FROM BRAZILIAN SANDY BEACHES

The new genus is characterised by the presence of a valvocopula with straight and smooth margins and by round and transapically elongated pores on its surface. The valvocopula fits beneath the raphe valve and covers the valve areolae and even sometimes the raphe. The internal and external raphe ends are simple. The areolae are occluded by fine porous hymenes on the raphid valve and they are coarser on the araphid valve. Two types of areolae are present around the margin of the araphid valve. The new genus is described from Brazilian sandy beaches (Porto Belo, Brazil) and Cocconeis disculoides Hustedt is transferred to Psammococconeis, establishing a new combination.

Distribution of living and dead diatoms in tidal wetlands of northern Japan: relations to taphonomy

This paper presents the results of a survey of the contemporary diatom distributions in four tidal marshes of eastern Hokkaido, northern Japan. Distribution of living diatom cells, as defined by cluster analysis, have relations to vegetation and substratum, and clearly to tide level. Comparison between living and dead diatoms in each cluster provides synecological information relating to diatom taphonomy in the tidal wetland environments. Four assemblages are recognized and they are summarized as follows. (1) An upland assemblage consisting of autochthonous freshwater diatoms adapted to relatively dry conditions. (2) A high marsh assemblage formed at or slightly above mean high tide level (MHTL) with only few allochthonous components. (3) A low marsh assemblage formed below MHTL. Dead valves within this assemblage are repeated widely redistributed by tidal processes. This assemblage is therefore a ‘mixed assemblage’ comprising a combination of allochthonous and autochthonous diatoms. (4) A tidal flat assemblage. On death diatom valves in tidal flat are immediately redistributed by tidal currents, and the dead diatom assemblage here has the characteristics of an ‘autochthonous’ or ‘residual’ assemblage. Autecological perspectives based on the distribution patterns can advance these interpretations. Dead valves of the epiphytic diatom Cocconeis scutellum, which possesses a raphid valve (R-valve) and a rapheless valve (P-valve), are common on two transects but only P-valves are widely distributed beyond the seaweed zone which represents the actual habitat of this species. Such selective processes are related mainly to the life form characteristics of monoraphid species: only R-valves remain attached to their substratum on death. The tychoplankton Paralia sp. is also a widely distributed species. In the case of Paralia, their long chains float more readily than other specimens are transported easily by tidal currents, and then trapped in entire tidal environments. These observations suggest it is likely that concentrations of only P-valves of C. scutellum or Paralia in the tidal marsh deposits should be treated as allochthonous components in the diatom assemblage.

Morphology of the marine epiphytic diatom Cocconeis heteroidea (Bacillariophyceae)

SUMMARY The morphology and fine valve structure of the marine epiphytic diatom Cocconeis heteroidea Hantzsch have been investigated. The entire frustule, including the internal and external structure of the raphid valve (RV) and araphid valve (AV), and the complete cingulum, are described using light microscopy and scanning and transmission electron microscopy, using a bleaching method. The strongly sigmoid raphe terminates in elongate hooked helictoglossae internally. The hymenes, with perforations arranged in a centric array, are located near the internal openings of the areolae in the RV. The striae in the AV consist of alveoli occluded by hymenes, that have perforations arranged in a parallel array and are located near the outer surface. The complete cingulum of AV consists of three open bands without fimbriae: a valvocopula, a copula with a ligula and a pleura with a small ligula. The RV has only a valvocopula which is open type and not fimbriate.

A new marine diatom, Cocconeis shikinensis sp. nov. (Bacillariophyceae) from Japan

SUMMARY A new species of Cocconeis has been found growing on the green seaweed Caulerpa racemosa (Forsskal) J. Agardh var. laete-virens (Montagne) Weber van Bosse from Shikine Island in the Izu Islands on the Pacific coast of Japan; we propose the name Cocconeis shiki-nensis Hid. Suzuki and describe the species by light microscopy (LM) and electron microscopy (EM). This taxon was also collected from the plastic plates used for rearing in seed production systems of the abalone Nordotis discus hannai Ino and the horned turban Turbo cornutus Solander in the Toyama Prefectural Fisheries Research Institute facing the Sea of Japan. The main morphological features of C. shikinensis are as follows. The valves are elliptic. The valve face of the raphid valve (RV) is slightly concave and that of the araphid valve (AV) is complementary to the RV and convex. The single plastid is flat, C-shaped and elaborately lobed. The raphe on the RV is straight. The each terminal area expands to both sides along the valve margin, forming an arrowhead-shaped, thickened hyaline area. The striae consist of small, round areolae and are radiate and uniseriate. On the AV, the striae consist of several alveoli. Each alveolus opens internally by means of a circular foramen. The valvocopula of each valve is fimbriate and open. The cingulum attached to the AV consists of three girdle bands; a valvocopula and two bands (copula and pleura), which are open and have ligulae. The relationship between C. shikinensis and similar members of the genus Cocconeis is discussed.

MORPHOLOGY OF THE MARINE DIATOM COCCONEIS PSEUDOMARGINATA GREGORY VAR. INTERMEDIA GRUNOW

The morphology and fine valve structure of the marine attached diatom Cocconeis pseudomarginata Gregory var. intermedia Grunow was investigated. The entire frustule, internal and external structures of the raphid and araphid valves and complete cingulum are described using not only the light microscope and scanning and transmission electron microscope but also bleaching method and the focused ion beam technique. The raphe that terminates with a comma-shaped helictoglossa internally is slightly sigmoid. The hymenes, with perforations arranged in a centric array, are located near the internal openings of the areolae in the raphid valve (RV). The striae in the araphid valve (AV) consist of alveoli occluded by hymenes that have perforations arranged in a parallel array and locate near the outer surface. The complete cingulum of AV consists of an afimbriate, open valvocopula and two bands with small ligula. The RV has only a valvocopula which is open type and not fimbriate.

SEXUAL REPRODUCTION AND AUXOSPORE FORMATION OF THE MARINE MONORAPHID DIATOM COCCONEIS PELLUCIDA

Sexual reproduction and auxospore formation of Cocconeis pellucida have been observed using a laboratory culture. This diatom was monoecious. Auxospores occurred at 18°C and 14°C, but not at 5°C. One gamete is formed in a gametangium, without cytokinesis. Each gametangium secretes gelatinous material near where it contacts the other gametangium. Sexual reproduction occurs via behavioural anisogamy and the single auxospore expands spherically. Sexual reproduction and auxospore formation corresponds to Type IIB1 of Geitler's system. The perizonium consists of transverse bands, which exhibit a marked dorsal angle on the dorsal side of the auxospore. The open ends of the transverse bands converge towards the centre of the ventral side of the auxospore, instead of forming a suture as in other pennate diatoms. The auxospore forms first a raphid concave valve and then an araphid convex valve. The initial cell is like a vegetative cell, except for the presence of two plastids. C. pellucida differs from C. placentula in the presence of a raphid valve in the initial cell, the absence of unequal cytokinesis during gametogenesis, delay in the division of the initial cell until after it has left the perizonium, and survival of both daughter cells following division of the initial cell. Cocconeis is unique among pennate diatoms in the formation of a spherical auxospore and die proportional decrease of valve length and width during the life cycle, which are otherwise characteristic of centric diatoms.

COCCONEIS SEDIMENTARIASP. NOV. (BACILLARIOPHYTA), A MARINE DIATOM FROM THE SOUTHEASTERN COASTAL WATERS OF THE PACIFIC OCEAN

Cocconeis sedimentaria sp. nov. usually occurs associated with SE Pacific bottom sediments but is also epiphytic on green macroalgae. The valves are frequently orbicular, 13-35 μm long and the transapical axis 10-27 μm wide. The sternum valve (or araphid valve) is only submarginally convex, depressed towards the margins and concave towards the sternum. The raphe-stemum valve (or raphid valve) is submarginally concave, elevated towards the sternum and the valvar margin. The raphe is straight and filiform and lies in a narrow sternum. The valvocopula is open at one end and bears fimbriae. Both valves have uniseriate striae. Morphological and structural relationships with similar taxa are discussed.

SEQUENTIAL VALVE DEVELOPMENT IN THE MONORAPHID DIATOMACHNANTHES MINUTISSIMAVAR.SAPROPHILA

Valve development has been examined in Achnanthes minutissima var. saprophila H. Kobayasi & Mayama. The formation of the raphid valve (RV) proceeds in the same sequence as has previously been described for Navicula. Early development of the araphid yalve (AV) is remarkably similar to that of the RV, in that a primary central rib and primordial central nodule are initiated, followed by the development of secondary arms from the centre and the recurring of the primary rib at the poles. Therefore raphe slits appear both at the centre and poles during the early development of the AV. However, thin fin-like depositions arise along the primary central rib between the secondary arms extending out from the centre and the centripetal extensions of the primary central rib recurring from the poles. The fins then fuse with the secondary arms and the in-turned primary central rib, so that the initially-formed raphe slits do not develop any further and are filled in: an axial area devoid of a raphe is thus formed. The ...

Observations on the valve structure of marine species of the diatom genus Cocconeis Ehr.

The valve structure of three marine diatom species, Cocconeis molesta var. crucifera, C. dirupta and C. pellucida was studied by transmission and scanning electron microscopy. In all Cocconeis examined, the areolae are occluded by hymenes located near the internal openings in the raphid valve and near the internal openings in the araphid valves.

VALVE MORPHOGENESIS IN THE PENNATE DIATOM ACHNANTHES COARCTATA

ABSTRACTMitosis and valve morphogenesis in the pennate diatom Achnanthes coarctata (Bréb. in W. Sm.) Grun. are described. After cytokinesis, both daughter nuclei and their microtubule centers (MCs) are found near one side of the cell. Each new tubular silica deposition vesicle (SDV) arises centrally, forming a single rib running the length of the cell. Each MC then migrates around its nucleus and positions itself directly adjacent to the new SDV. The enlarging silicalemmas with their associated MCs, nuclei, microtubules (MTs) and microfilaments (MFs) appear in mirror image in the daughter cells. Both SDVs soon generate a second longitudinal rib alongside the first; the gap between the ribs ultimately becomes the future raphe fissure. The MC, MTs and nucleus are associated with each fissure. However, the subsequent behavior of the valve secreting machinery now becomes quite different in the daughter cells. In the cell that will form a raphid valve, the silicalemma, flanked by MFs, expands laterally in both directions over the cleavage furrow. Within the expanding SDV, silica secretion continues, eventually generating the structure of the mature valve, and during this phase the raphe fissure becomes delineated as in other raphid diatoms. In the other daughter cell, however, the MC and its MTs withdraw from the silicalemma, and the SDV moves laterally across the cleavage furrow until the double rib is at the corner of the cell. As silica is secreted into this expanding SDV, the raphe fissure completely fills in. This valve, therefore, lacks a raphe when mature and has a symmetry quite different from that of the valve formed in the other daughter cell. These events are compared with the course of morphogenesis described for other raphid diatoms.

STRUCTURE, LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). IV. CORRELATION OF SIZE REDUCTION WITH CHANGES IN VALVE MORPHOLOGY OF RH. GENUFLEXA1

ABSTRACT Rhoicosphenia Grun. is a relatively isolated genus among the biraphid diatoms. Morphological changes in an isopolar member of the genus, Rh. genuflexa (Kütz.) Medlin, were investigated using light and scanning electron microscopy. The fully raphid valve showed changes in its flexure that could be correlated with size reduction during its life history from the initial cells to the smallest cells found in the population. Bands showed changes in number (from three to one) related to size reduction. Rh. genuflexa is morphologically similar to Rh. abbreviata (C. Ag.) Lange‐Bert. (=Rh. curvata (Kütz.) Grun.), although the two are distinct taxa. These observations support previous contentions that Rhoicosphenia is a natural taxonomic grouping.

Variability in the structure of the genus Cocconeis Èhr. (Bacillariophyta) with special reference to the cingulum

The morphology and fine structure of six species of the monoraphid diatom genus Cocconeis Ehr. have been investigated. The raphid valve is concave and thinner than the convex araphid valve. The vel...