Raphe Sternum Research Articles

Gyrosigma dongtingense sp. nov. (Bacillariophyta) from Dongting Lake, China

Dongting Lake is China’s second largest freshwater lake; some new diatom species have been described from this lake recently. The current study describes a new diatom species from this lake, Gyrosigma dongtingense sp. nov. Gyrosigma dongtingense sp. nov. belongs to the section Strigiles sensu H. Peragallo and it is characterized by: 1) its large cell size (valves are 161–218 μm long and 24–29 μm wide), 2) having two curvatures for each half of its raphe sternum, 3) the transverse stria density (12–14 in 10 μm) lower than the longitudinal stria density (16–18 in 10 μm), 4) both the external proximal raphe fissures deflecting towards the convex side of each corresponding half-valve, 5) T-shaped internal proximal raphe fissures, and 6) a prominent axial costa presents along the primary side of the raphe sternum. The isomorphism and dimorphism of the external proximal raphe fissures are reviewed, and similar taxa are discussed.

Fallacia fawensis sp. nov., a new brackish water diatom (Bacillariophyceae) from Southern Iraq

The diatom genus Fallacia includes species having a conopeum which is a perforated thin sheath of silica lying along the apical axis on the external valve face and a hyaline lateral area in the internal valve face. In surveying the benthic diatoms of Basra, a new small brackish water species, Fallacia fawensis was found associated with fine-grained substrata on the western bank of Shatt Al–Arab River, Southern Iraq. This epipelic species is described based on light and scanning electron microscopy and characterized by having a porous conopeum covering the area between raphe sterna and mantle, narrow elongated marginal striae, and a structure similar to lateral hyaline areas in the valve internal side. The terminal raphe endings on the external valve face, below valve apex, the raphe sternum inner margins come close to each other, blocking raphe canal but leaving a lacuna-like thin groove for connection with the deflected upper part of the open raphe canal. These features separated this species from allied taxa of the genus and also from closely related genera, Pseudofallacia and Germaniella. Notes on the ecology and distribution of the new species as well as the associated diatom taxa are provided.

<p><strong><em>Scoliolyra</em> <em>elliptica</em> gen. et sp. nov. (Bacillariophyceae), a new marine genus from sandy beach in Southern China</strong></p>

Observation of sand samples collected from an estuarine sandy beach in Southern China revealed the presence of a new biraphid diatom. It is characterized by the presence of a twisted raphe system, apically elongate areolae, and striae interrupted by longitudinal H-shaped lateral areas in a form of valve face depressions, as well as girdle composed of open, plain copulae. The structure of valve outline, the raphe sternum and striae bears some resemblance to some established genera including e.g., Lyrella, Fallacia, Scolioneis, Scoliopleura and Scoliotropis, however, these characters are uniquely combined in this novel taxon. The new species, Scoliolyra elliptica, belongs to a new biraphid genus, Scoliolyra, and it is tentatively placed within the family Scolioneidaceae.

Halamphora primus (Bacillariophyta): a new diatom species from the Gulf of California, Mexico

A new diatom species, Halamphora primus sp. nov. is here proposed, and described based on comparison of morphological traits. This new taxon has semi-lanceolate valves, strongly dorsiventral. Its ventral margin goes from slightly concave in the mid part to lightly convex toward the eccentric parts. Unlike most species of Amphora sensu lato that have the raphe distal ends curved dorsally, in H. primus these are curved ventrally. A ledge is present on the dorsal side of raphe, and a short conopeum extends along the raphe sternum fading before reaching the apices. A dorsal fascia is absent. Specimens were collected along with a highly diverse taxocoenosis (S=281) from the skin of stonefish in the Gulf of California, Mexico. However, the scarceness of H. primus frustules in the sampled taxocoenosis strongly suggests that it is not an epizoic form of the stonefish.

Gyrosigma xiamenense sp. nov. (Bacillariophyta) from the middle intertidal zone, Xiamen Bay, southern China

Gyrosigma xiamenense sp. nov., a new diatom species from the middle intertidal zone, Xiamen Bay, southern China, was studied by light and scanning electron microscopy. The valves are large and sigmoid, with parallel sides. The raphe sternum has single curvature. Externally, a row of round pores is present on the mantle; isomorphic proximal raphe fissures turn first in opposite directions, then both final parts of the fissures run nearly parallel to the longitudinal striae. Internally, a row of areolae closest to the raphe sternum is capped by small projections on the primary side whilst these are absent on the secondary side; proximal raphe endings are first club-shaped, then the final parts of the two raphe endings form two T-shaped slits being separated from the club-shaped part by a tiny bridge; there is a vermiform bar in the middle of the raphe nodule. G. xiamenense is epipelic and lives in marine habitats.

A comparative study of Pleurosigma subrectum and P. acus (Bacillariophyta)

In continuation of an earlier paper on Pleurosigma species with an (almost) non-sigmoid valve and raphe sternum, a comparative study was made in LM and SEM of Pleurosigma subrectum and P. acus. For P. subrectum, slides and a subsample of the type material were examined. For P. acus no unmounted material permitting SEM investigation is extant; a sample containing specimens fully matching the type in LM was therefore used as epitype material for SEM. The original data on striation of P. acus are emended. No morphological differences indicating separate specific status of these two taxa were observed and P. acus is therefore here designated a heterotypic synonym of P. subrectum. From the data now available, this is a very widely distributed species. The study demonstrates the indispensable role of collections for investigations on the diversity and distribution of diatom species.

Madinithidium gen. nov. (Bacillariophyceae), a new monoraphid diatom genus from the tropical marine coastal zone

:We studied a group of monoraphid diatom species (Bacillariophyceae, Achnanthidiaceae) found in the marine coastal environment of tropical islands of the Caribbean Sea, western Atlantic Ocean, Indian Ocean, South Pacific Ocean, the Adriatic Sea and the Black Sea. Based on light and electron microscope examination, Madinithidium was formally described as a genus new to science with the generitype defined as Madinithidium undulatum. The characteristic features of the valve structure are a strongly developed sternum and raphe sternum, transapical striae formed by a single areola (macroareolae) positioned in small depressions, elevated virgae and coaxial internal central raphe endings. Furthermore, the striae of both raphe and sternum valves are closed by finely perforated hymenes. Madinithidium and Achnanthidium species are difficult to identify correctly with light microscopy since their valves are small and finely structured. Four species recently described from the western Indian Ocean and assigned to Achnanthidium sensu lato – Achnanthidium capitatum, A. flexuistriatum, A. pseudodelicatissimum and A. scalariforme – possessed morphological features permitting their placement into Madinithidium gen. nov. The above-mentioned species were formally transferred to the new genus.

Morphological and molecular phylogenetic analysis of the high triglyceride‐producing marine diatom, Fistulifera solaris sp. nov. (Bacillariophyceae)

SummaryFistulifera sp. strain JPCC DA0580, a marine pennate diatom, contains extremely high levels of intracellular triglyceride and has been suggested as a promising source of feedstock for biodiesel fuels. JPCC DA0580 was isolated from a mangrove swamp located in Sumiyo Bay below the mouths of the Sumiyo and Yakugachi Rivers in Amami‐Ohshima, Kagoshima, Japan. In this study, the morphology and the 18S rDNA sequence of JPCC DA0580 were compared with those of other Fistulifera strains. JPCC DA0580 possesses morphological characters of the genus Fistulifera, namely lightly silicified frustules, a distinct median costa (raphe sternum), and a wart‐like central pore (fistula). Morphometric analysis revealed that JPCC DA0580 differs from other Fistulifera species by the presence of a valve with coarser striation and coarser areolation. On the basis of 18S rDNA phylogeny, JPCC DA0580 formed a well‐supported clade with other members of the Fistulifera species complex, although the number of nucleotide substitutions was highest in JPCC DA0580. Our results led us to propose the taxonomic name Fistulifera solaris sp. nov. for JPCC DA0580.

Typification and taxonomy of Gyrosigma tenuissimum (W. Sm.) J.W. Griffith & Henfr., comparison with Gyrosigma coelophilum N. Okamoto & Nagumo and description of two new taxa: Gyrosigma tenuissimum var. gundulae var. nov. and Gyrosigma baculum sp. nov. (Pleurosigmataceae, Bacillariophyta)

Gyrosigma tenuissimum (W.Sm.) J.W.Griffith & Henfr. was examined in the original material and an emended description is presented. Its protologue contains an error of taxonomic significance: in the type material, the valve and raphe sternum do not show the considerable flexure described and illustrated in Smith (1853). A comparison with Gyrosigma coelophilum N. Okamoto & Nagumo revealed that the latter, although similar in several characters, differs sufficiently in others to warrant separate specific status. Descriptions of two new taxa are given: Gyrosigma tenuissimum var. gundulae var. nov. and Gyrosigma baculum sp. nov. Both show very fine longitudinal striae at or beyond the limit of ordinary light microscopy and are practically non-sigmoid

Pleurosigma guarreranum, sp. nov. (Pleurosigmataceae, Bacillariophyta), from the Gulf of San Matías, Argentina, and comparison with the allied species Pleurosigma exemptum and P. obesum

A new marine diatom, Pleurosigma guarreranum Sar, Sterrenburg & Sunesen, sp. nov., is described with light and electron microscopy from material collected in coastal waters of the Gulf of San Matías, Río Negro Province, Argentina. Pleurosigma guarreranum resembles P. exemptum and P. obesum from the Philippines. Isotypes of P. exemptum and P. obesum deposited in the Albert Mann Collection, National Museum of Natural History, Smithsonian Institution (US), were examined with light microscopy. The observations supported a previous suggestion to include P. obesum as a heterotypic synonym of P. exemptum, which has priority. Since there is no available unmounted original material of P. exemptum, a comparative light microscopical analysis of P. guarreranum and the type material of P. exemptum was made. Despite some similarities, there are subtle differences in morphometric data, valve outline, raphe sternum pattern, and morphology of the central area. But especially, the two species consistently differ in the angle of intersection of the oblique striae, justifying a separate taxonomic position. Pleurosigma guarreranum was also compared with another species belonging to the section Formosi, P. decorum, similar in valve outline, raphe sternum pattern and angle of intersection of the oblique striae.

Cocconeis thalassiana sp. nov., a new alveolate diatom (Bacillariophyta) from the Mexican Caribbean

Based on light and scanning electron microscopy observations, a detailed description of a new marine alveolate Cocconeis Ehrenberg, C. thalassiana sp. nov., is presented. This large Cocconeis was found in samples collected from a shallow marine coastal lagoon of the Mexican Caribbean, as an epiphyte on the marine seagrass Thalassia testudinum Banks ex König. Among alveolate Cocconeis, the presence of long alveoli for every stria opening into the frustule interior by two long internal apertures of the sternum valve (SV) is a unique character. Other typical frustule features are: bilayered, convex SV thicker than the concave raphe–sternum valve (RSV), the inner face of the SV with hyaline areas between the two apical rows of apertures, the monolayered RSV with a narrow submarginal hyaline area following the valve outline, and the girdle consisting of only two valvocopulae (one for each valve).

SCALY INCUNABULA, AUXOSPORE DEVELOPMENT, AND GIRDLE POLYMORPHISM IN SELLAPHORA MARVANII SP. NOV. (BACILLARIOPHYCEAE)(1).

Uniparental auxosporulation was observed in a monoclonal culture of a Sellaphora clone isolated from the epipelon of a fishpond in the Czech Republic. The cox1 sequence for the clone confirmed that it belonged to the Sellaphora pupula-bacillum species complex but showed significant differences from all previously characterized Sellaphora species, and it is therefore described as S. marvanii sp. nov. Protoplast, valve, and girdle structure resembled those of other Sellaphora species, but a novel finding for all diatoms was a change in girdle structure during the life cycle: the most advalvar girdle band (valvocopula) bore a single line of pores in enlarged postauxospore cells but was entirely plain in small cells and gametangia. The young auxospores were covered by incunabula containing large, delicate, ± circular scales, resembling those of centric diatom auxospores; similar scales have been reported in a few other raphid diatoms (Pseudo-nitzschia multiseries, Diploneis sp.) but contrast with the strip incunabula of some Nitzschia and Pinnularia and the helmet-like caps of Neidium. The scales persisted during auxospore expansion, mostly as two caps over the auxospore poles. The transverse perizonium comprised a very wide, closed primary band, flanked by numerous secondary bands whose open ends were strongly incurved toward the center. Initial valves were differentiated from their immediate descendants by the very strong external demarcation of the raphe sternum, irregular shape, and curved transapical profile.

Encyonema exuberans sp. nov. (Bacillariophyceae) from southern Brazilian lotic systems

Abstract: Despite the relatively large number of species illustrated in the recent freshwater flora of South America, specific studies concerning cymbelloid taxa are still rare in the continent. The analysis of several samples collected in the southern region of Brazil (states of Parana and Rio Grande do Sul) revealed the existence of an interesting Encyonema living in the epilithon of lotic environments. This paper describes and illustrates in detail the morphology of the new diatom Encyonema exuberans examined with light and scanning electron microscopy. Distinctive morphological features of this new species include valve shape, the strongly radiate and denser striation near the poles and the indistinct intermissio. The rostrate ends are always ventrally bent. The striae are composed of areolae with different sizes and shapes and are often uniseriate. Double rows of areolae are visible on the dorsal ends and near the raphe sternum. In external view, the central stria ends in a round stigmoid. The transapical dorsal ribs and the areolation patterns are a unique combination of features not known in any diatom belonging to the genus Encyonema, making them decisive taxonomic characters to distinguish this species within this genus.

Morphological observation of Epithemia ocellata (Ehr.) Kütz. (Bacillariophyceae) from China

The species of Epithemia ocellata (Ehr.) Kutz. from Northeastern China were observed by scanning electron microscopy (SEM). The studies on silica valve formation in different stages were made. At the early stage, a Y-shaped raphe sternum was found. Areolae were made from virgae and vimines. In immature valves, the canal formation before the raphe fissure is visible. The raphe system, virgae and vimines (areolae) might be the early siliceous elements of the valve during morphogenesis. The formations of virgae and vimines are similar to that of Gephyria media W. Arnott. Rows of silica papillae formed gradually on the face of the valve. After the areolae were covered with silica and form rows of papillae, the outer valve surface could become mature. Details of the internal costae were observed in mature valves.

Studies on Amphora subgenus Halamphora (Bacillariophyta): the revision of some species described by Hustedt using type material

As part of an analysis of type material of Amphora species described by Hustedt, the lectotypes of Amphora fontinalis, A. rugosa and A. schroederi and the holotype of A. subturgida were analysed. Light microscopy showed that all these tropical freshwater taxa are similar in frustule and valve outline, position of the raphe, appearance of the dorsal striae and thickening of the central dorsal virgae. Scanning electron microscopy allowed reliable differentiation between the four, based on the morphology of dorsal striae, dorsal areolae, conopeum, proximal raphe fissures, presence or absence of an inner longitudinal rib close to the raphe sternum, and degree of thickening of the central dorsal virgae. Previous reports of A. fontinalis from Tahiti and Moorea were confirmed while reports of this species from Australia and of A. subturgida from Mauritius, Papua and Israel were refuted. Based on our results, species descriptions are emended and the distributions of these four species are revised. Comparisons of these species and others of the subgenus Halamphora are presented.

Valve Morphogenesis in the Diatom Genus Pleurosigma W. Smith(Bacillariophyceae): Nature's Alternative Sandwich

The loculate ("chambered") valve structure of centric diatoms like Triceratium favus Ehrenberg has been mentioned time and again in the nanostructure literature. Here we draw attention to the fundamentally different alternative sandwich model nature developed in the genus Pleurosigma, where it is nonloculate. This has so far been overlooked in nanostructural studies. We suggest some mechanical aspects that would offer interesting avenues for experimental testing. The first description of the natural fabrication process ("morphogenesis") is presented. This begins with the development of the raphe sternum, which then acts as a rigid backbone. The inner layer of the sandwich-structured valve develops next, with relatively large +/- round single internal foramina not yet closed by a sieve membrane, in offset arrangement. This serves as a substrate for rows of stubby hollow pillars, also in offset arrangement. Then the outer layer of the sandwich develops and two different patterns ("coarse-mesh" and "stellate bridges") have been observed. At first, the external areolar foramina are relatively large and +/- oval, gradually filling up until the tiny slits characteristic of the genus remain. In Pleurosigma species with double internal areolar foramina, small bridges grow from the opposite margins of the single foramina until they fuse. The sieve-membranes then close the internal areolar foramina. The finished valve is a lightweight structure expected to offer excellent strength with parsimonious expenditure of the raw material-silica.

VARIATION IN PATTERNS OF VALVE MORPHOGENESIS BETWEEN REPRESENTATIVES OF SIX BIRAPHID DIATOM GENERA (BACILLARIOPHYCEAE)

Scanning electron microscopic studies of silica valve formation in naviculoid diatoms representing six different genera revealed that the precise sequence of depositional events varied among genera. Valve deposition begins with the formation of the raphe sternum, from which virgae (lateral outgrowths) extend. Areolae (pores) are formed between the virgae by the fusion of cross‐extensions (vimines). In most of the species studied (Craticula ambigua (Kützing) D. G. Mann, Frustulia vulgaris (Thwaites) De Toni, Craspedostauros australis E. J. Cox, and Gomphonema truncatum Ehrenberg), areola (pore) formation began near the raphe sternum before completion of the valve margin, but in Pinnularia gibba Ehrenberg the valve margin fused before the areolae were formed. Silica deposition in all these taxa was mainly distal to proximal (with respect to the cytoplasm), but in Haslea sp. it was mainly proximal to distal. Haslea also differed in that areolae were defined as the valve margin was completed. These data have also contributed to the interpretation of taxonomically important features, such as raphe endings. In P. gibba the internal central raphe fissures were laterally deflected but subsequently obscured by additional silicification of the valve, whereas in G. truncatum they were initially straight, becoming laterally deflected as valves mature. External raphe fissures in Frustulia became Y‐shaped only just before maturity; in immature valves they were dotlike, as in Amphipleura Kützing. The comparison of developmental pathways in diatoms is a useful adjunct to morphological and other approaches in diatom systematics and warrants renewed attention.

Diploneis sejuncta (Bacillariophyta) and some new species from an ancient lineage

A group of unusual Diploneis species has been examined using light and scanning electron microscopy. Diploneis sejuncta is peculiar in Diploneis because its longitudinal canals are separated from the raphe sternum furrows, whereas in most other species they are adjacent. Diploneis sejuncta f. constricta has also been examined and is elevated to specific rank as D. solea. A fossil member of the group, Navicula sejuncta var. baldjikiana from upper Miocene deposits from eastern Europe is intermediate in morphology between D. sejuncta and D. solea and is elevated to specific level as D. praesejuncta. Three other species related to D. sejuncta are described for the first time: D. pneumatica, D. biremijormis, and D. colae. All members of this group share a distinctive zig-zag arrangement of internal pores; the same arrangement is present in D. totarae, an upper Eocene diatom described from Oamaru, New Zealand, suggesting that this species lineage is at least 37 million years old. The implications of this are discussed with respect to current trends in species-level diatom taxonomy. The generic position of D. sejuncta and its relatives is discussed in relation to the peculiar longitudinal canal and pore features, and it is argued that more characters link the group with Diploneis than with any other known genus and that the current understanding of that genus is too poor to make a sound judgement as to whether or not a new genus is justified.

STUDIES ON THE GENERAGYROSIGMAANDPLEUROSIGMA(BACILLARIOPHYCEAE) RULES CONTROLLING RAPHE FISSURE MORPHOGENESIS INGYROSIGMA

The type of central raphe fissure deflection distinguishes two major sections of the genus Gyrosigma: one containing dimorphic, the other isomorphic species. Both dimorphism and isomorphism are governed by strict rules. Isomorphic species exclusively show deflection to the convexity of the raphe sternum, dimorphic Gyrosigmas exhibit a “handedness”, i.e. the central raphe fissures exclusively deflect to the left in all species examined.

STUDIES ON THE GENERAGYROSIGMAANDPLEUROSIGMA(BACILLARIOPHYCEAE)

The intersection angle of the oblique striae in Pleurosigma, the difference in the densities of the longitudinal and transverse striae in Gyrosigma and the single or double curvature of the raphe sternum in both Gyrosigma and Pleurosigma permit distinction of subgroups in these genera. Four new light microscopical criteria: the colour in darkfield, the raphe angle, the apical details and the position of the terminal areas, are suitable for taxonomy. Additional light microscopical features are discussed. The findings are based on populations of different origins for 31 species. A new species, Pleurosigma curiosa van den Heuvel is described.