Terminal Raphe Fissures Research Articles

Three new Eunotia (Bacillariophyta) species from Acadia National Park, Maine, USA

Three new species in the diatom genus Eunotia were found in the freshwater ponds and streams of Acadia National Park, Maine, USA. Eunotia novaeangliae sp. nov. belongs to the E. incisa group, species with nose-like apices and terminal raphe fissures distant from the ends. It is most similar to E. tenelloides in that species cluster, although differs in the valve shape, geographical distribution, several ultrastructural details and slight but consistent differences in valve dimensions and striae density. Eunotia panda sp. nov. is in the E. bilunaris group, species with slight even curvature and smooth margins of the valves. However, E. panda can be distinguished from E. bilunaris by dorsally slightly recurved apices with rounded ends, ultrastructural details and noticeably constant valve width. Eunotia spatulata sp. nov. is most similar to E. eurycephala, but differs from that taxon by having straighter and significantly larger valves with more swollen apices. All three taxa were sufficiently abundant in the samples collected from the park that they could be found in both SEM and LM microscopes. Eunotia novaeangliae and E. panda have both been illustrated in other publications before but not named. All three species occurred in waters of low conductivity and pH, typical for the genus. Acadia National Park appears to be a hotspot for Eunotia species diversity, and further study of the oligotrophic waters of this site is certainly warranted.

Análisis de los materiales tipo de Pleurosigma formosum y P. decorum (Pleurosigmataceae, Bacillariophyta).

Análisis de los materiales tipo de Pleurosigma formosum y P. decorum (Pleurosigmataceae, Bacillariophyta). Los materiales tipo de Pleurosigma formosum W. Smith y P. decorum W. Smith fueron examinados. Ambas especies fueron separadas hasta ahora por el rango de tamaño, la forma de la valva y la densidad de las estrías sobre la base de su análisis con microscopio óptico (MO). Sin embargo, los materiales tipo muestran alguna superposición en los rangos de tamaño y densidad de estrías, con sutiles diferencias en el ángulo de intersección de las estrías oblicuas, el cual es algo más pequeño en P. decorum. El análisis con microscopio electrónico de barrido (MEB) muestra que ambas especies comparten algunos caracteres ultraestructurales tales como el engrosamiento en forma de silla de montar del nódulo central del rafe, la amplia superposición de las fisuras centrales del rafe, la forma de las fisuras terminales del rafe, en gancho corto, la morfología general de los poros internos ocluidos por un himen cruzado por una barra hundida y la presencia de algunos pares esparcidos de poros más profundamente excavados, carentes de barra. Sin embargo, los especímenes tipo difieren en la morfología interna de los poros areolares ocluidos por un himen. Estos son circulares, cruzados por una barra hundida y con bordes engrosados en P. formosum y sub-circulares a elípticos, cruzados por una barra menos hundida y sin bordes engrosados en P. decorum. Los resultados del análisis con MEB apoyan el punto de vista de Hendey acerca de que P. decorum y P. formosum son especies separadas pero cercanamente relacionadas.

Morphology, ecology and biogeography of Stauroneis pachycephala P.T. Cleve (Bacillariophyta) and its transfer to the genus Envekadea

Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA) and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are described in this article. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the valves and copulae is smooth and lacks ornamentation. We also examined the type material of S. pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectotype is designated.

Pleurosigma hinzianum sp. nov. and P. frenguellianum sp. nov. (Pleurosigmataceae, Bacillariophyta) from Argentinean coastal waters, in comparison with P. amara Stidolph and P. elongatum W. Smith

Two new marine diatom species from Argentinean coastal waters, Pleurosigma hinzianum Sterrenburg, Sunesen & Sar, sp. nov. and P. frenguellianum Sunesen, Sterrenburg & Sar, sp. nov., are described. The characters permitting their identification are specified, based on comparison with type material of the morphologically similar species P. amara Stidolph and P. elongatum W. Smith in the light (LM) and scanning electron microscope (SEM). New information on the type material of P. elongatum is presented and its taxonomic concept is emended. The main criteria for separation of the species discussed here are: valve outline, path of the raphe-sternum, raphe angle and angle of intersection of the oblique striae in LM; and external central and terminal raphe fissures, internal details of the central area, external and internal apical structure, and morphology of the hymen-occluded internal pores in SEM. The occurrence of these (and probably other) species in the genus Pleurosigma in net samples is adventitious and not indicative of a true planktonic mode of life.

Achnanthidium palmeti (Bacillariophyta, Achnanthidiaceae), a new freshwater species from Réunion Island

Recent survey of the epilithic diatoms in the running waters of Réunion Island led to the discovery of a new species of Achnanthidium. Achnanthidium palmeti sp. nov. belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to the same side of the valve. The new species differs from other taxa in this group by a higher stria density and the areolae morphology along the axial area; moreover, apart from Achnanthidium latecephalum H. Kobayasi, A. palmeti sp. nov. is the only species having raphe vestiges. The new species was found in oligotrophic waters with very low conductivity and circumneutral pH.

Achnanthidium delmontii sp. nov., a new species from French rivers.

A new freshwater diatom species belonging to the genus Achnanthidium KĂźtz. has been found in several French rivers namely those of the Languedoc-Roussillon and Rhin-Meuse regions. Achnanthidium delmontii sp. nov. is described based on light and scanning electron microscopy observations. This species belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to the same side of the valve and it is compared to the most related species: Achnanthidium pfisteri Lange-Bertalot, Achnanthidium pyrenaicum (Husdedt) Kobayasi, Achnanthidium temniskovae Ivanov et Ector and Achnanthidium zhakovschikovii Potapova. The assessment of its ecology was made through physicochemical analysis carried out on sites which are part of water quality monitoring networks. Some comments are made on the rapid expansion of Achnanthidium delmontii sp. nov.

New species and combinations in monoraphid diatoms (family Achnanthidiaceae) from North America

This article clarifies the taxonomy and nomenclature of several monoraphid diatom species found in rivers and lakes of North America. The morphology of these diatoms is studied with light and electron microscopy. A new combination Rossithidium anastasiae (Kaczmarska) Potapova is introduced for a species common in both Europe and North America and often misidentified as Achnanthes linearis (W. Smith) Grunow or R. linearis (W. Smith) Round et Bukhtiyarova. Achnanthes harveyi Reimer, often found in eastern North America, is transferred to Psammothidium Bukhtiyarova & Round on the basis of the convex raphe valve, uniseriate striae, and raphe structure. A new Psammothidium species, P. pennsylvanicum Potapova is described and compared with the most similar taxon, P. semiapertum (Hustedt) Aboal. Diatoms originally described as Achnanthes lutheri Hustedt and A. stewartii Patrick are transferred to the genus Platessa Lange-Bertalot on the basis of biseriate striae, flat valves, and the absence of terminal raphe fissures. Two new Platessa species, P. kingstonii Potapova and P. bahlsii Potapova are described from the eastern USA and compared with most similar species, P. lutheri (Hustedt) Potapova and P. conspicua (A. Mayer) Lange-Bertalot, respectively. Achnanthes lanceolata var. abbreviata Reimer, found in the southeastern USA, is shown to possess multiseriate striae and relatively long terminal raphe fissures characteristic for the genus Planothidium Round & Bukhtiyarova, to which it is transferred.

New Amphicocconeis species off Mascarenes (Western Indian Ocean) and related taxa

Two new species were found on coral sediments of Mascarene archipelago: Amphicocconeis mascarenica sp. nov., relatively frequent in Réunion and rare in Rodrigues Islands, and A. rodriguensis sp. nov., relatively rare in Rodrigues and scarce in Réunion. Comparison was made with A. disculoides and A. debesii (Hustedt) De Stefano, and with species pertaining to Psammococconeis Garcia (P. brasiliensis and P. disculoides sensu Garcia). The Mascarenes taxa do not have simple raphe endings but terminal raphe fissures bent to the same side, which is a characteristic feature shared by Amphicocconeis taxa. Amphicocconeis rodriguensis has a raphe valve relatively similar to that of A. debesii (Hustedt) De Stefano, but with a denser striation; furthermore, the valvocopula of the sternum valve is narrow with simple to chiselled fimbriae. Amphicocconeis rodriguensis sternum valve is close to that of A. debesii (Hustedt) De Stefano. Amphicocconeis mascarenica shows a number of striae relatively low on both valves and both valvocopulae are generally extended and present rows of alternated small holes, which seems a unique feature for Amphicocconeis.

Achnanthidium zhakovschikovii sp. nov. (Bacillariophyta) and related species from rivers of Northwestern Russia

Achnanthidium zhakovschikovii is described as a new epiphytic species from spring-fed rivers near St. Petersburg, Russia. This species belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to one side of the valve. The new species differs from other taxa in this group by the broadly linear to elliptical shape of the valve and the wide sternum of the rapheless valve. Achnanthidium zhakovschikovii and two other Achnanthidium species with curved raphe fissures, A. pyrenaicum (Hustedt) Kobayasi and A. thienemannii (Hustedt) Lange-Bertalot, are found in the St. Petersburg region, mostly in waters of relatively high mineral content.

TWO COMMON NORTH AMERICAN DIATOMS, ACHNANTHIDIUM RIVULARE SP. NOV. AND A. DEFLEXUM (REIMER) KINGSTON: MORPHOLOGY, ECOLOGY AND COMPARISON WITH RELATED SPECIES

Two species of Achnanthidium, which are fairly common in benthic samples collected from North American rivers, have posed considerable identification problems for analysts enumerating diatoms for water quality assessment programs in the United States. Both diatoms belong to the apparently diverse and insufficiently studied group of Achnanthidiumspecies with terminal raphe fissures sharply bent to the same side of the valve. The goal of this study was to clarify the taxonomic position of these taxa and document their morphology, ecology and distribution. One of these, Achnanthidium rivulare Potapova & Ponader sp. nov., is especially abundant in soft-water, phosphorus-poor rivers of coastal regions of North America, and has been confused in the past with various species of Achnanthidium and Rossithidium. This species is most similar to Achnanthidium convergens (Kobayasi) Kobayasi known from Japan and A. crassum (Hustedt) Potapova & Ponader comb. nov. Achnanthidium crassum is a poorly known species; therefore, SEM observations of its type material from Sumatra and another population from Hawaii are presented here. A second problematic North American species is A. deflexum (Reimer) Kingston, a diatom very similar in its morphology to A. pyrenaicum (Hustedt) Kobayasi. Study of the type materials and a number of other collections of these species with SEM and morphometric analysis of selected populations allowed us to conclude that A. deflexum, known from North America, and A. pyrenaicum, reported from Europe and Japan, are not conspecific. The shape and size of the frustule and the shape of the external areolae foramina are consistently different between the two species. Both A. deflexum and A. pyrenaicum are alkaliphilous, calciphilous diatoms, found mostly in phosphorus-poor waters.

NEIDIUM ALPINUMVAR.QUADRIPUNCTATUM(HUSTEDT) COMB. NOV., AN IMPORTANT ACIDOBIONTIC TAXON FROM NORTHEASTERN NORTH AMERICA

Navicula quadripunctata Hustedt, which has sometimes been synonymized with Neidium alpinum Hustedt, is distinct and recognized here as Neidium alpinum var. quadripunctatum (Hustedt) Hamilton, comb. nav. This taxon is distinguished from the nominate variety by its robust size, elliptical-linear shape, and narrowly rounded apices (length: 12–33 μm width: 3–7 μm; striae 30–38 in 10 μ). From SEM observations, it is evident that the bifurcate appearance of the terminal raphe fissures corresponds to a siliceous flap that covers the polar raphe endings, which are simple and straight. N. alpinum var. quadripunctatum is acidobiontic, commonly found in lakes and streams of pH 4.5–5.9. In North America, this diatom has been found in Ontario (Canada) and Alaska, Michigan, Minnesota, New Hampshire, New York, Pennsylvania and Wisconsin (U.S.A.).