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While conducting a systematic investigation of phytoplankton assemblages in the northeastern Gulf of Mexico (GOM) in the aftermath of the Deepwater Horizon blowout we took the opportunity to collect sediment samples from off the coast of Pensacola Bay, Florida. These samples contained sufficient numbers of a monoraphid diatom initially identified as Achnanthes controversa Hustedt (Navicula marginulata Cleve) to examine its fine structure in detail. The results of these investigations clearly show that this taxon could not be accommodated in Achnanthes as currently understood, or in any currently described genus in the Achnanthidiaceae. We, therefore, propose a new genus, Vallithidium, with Vallithidium marginulatum (Cleve), J.A. Nienow & A.K.S.K Prasad as the generitype. Our investigations also show that the taxon Hustedt illustrated from Campeche Bay is not the same as the taxon described from the northeastern Gulf. We therefore describe it as a separate species in the new genus, Vallithidium campechianum sp. nov. [ABSTRACT FROM AUTHOR]

During a survey of benthic diatoms from the coral reefs of the Indian Ocean (Scattered Islands) and Pacific Ocean (Tuamotu Archipelago), an interesting monoraphid diatom was observed and examined by light microscopy and various electron microscopy methods including Focus Ion Beam milling. Our thorough analysis revealed the similarity of this diatom to Bennettella R.W. Holmes, which we reference in the name: Xenobennettella Witkowski & Riaux-Gobin gen. nov., with Xenobennettella coralliensis Witkowski & Riaux-Gobin sp. nov. as the generitype. The type habitat for this new species is the sublittoral coral reef of Juan de Nova in the Mozambique Channel. The sternum valve of the new genus is characterized by an alveolate ultrastructure with the rim of the alveola opening along the valve margin, resembling the sternum valve of Bennettella. Internally, Xenobennettella differs from the latter by possessing a cavum (horseshoe-shaped chamber) on one side of the valve, in a central axial position. The raphe valve of Xenobennettella has small, marginal, apically elongate chambers, which are internally delineated by transapical ribs that are very similar to Bennettella. However, the raphe in the new genus is different from the latter, resembling some Cocconeis and Planothidium with internal raphe endings bent in the opposite direction, while resembling some Planothidium taxa externally by ending on the apical part of the mantle. This contrasts to Bennettella, which has a unique raphe system, with external raphe endings below the apices, a prominent axial structure and a transapically expanded central area. Likewise, the external surface of Bennettella is different from that of the new genus with a complex mantle structure and biseriate striae. In Xenobennettella, the valve mantle of the raphe valve is simple and perforated by areola. The transapical striae occur in the valve margin and the axial area is ornamented along its course with a single row of densely packed areola on both sides. The characteristics of the raphe valve and alveolate sternum valve place the new genus among the Achnanthidiaceae. [ABSTRACT FROM AUTHOR]

Six species of the genus Achnanthidium Kütz. with straight terminal raphe fissures including Achnanthidium caledonicum (Lange-Bert.) Lange-Bert., A. sieminskae Witkowski, Kulikowskiy & Riaux-Gob., Achnanthidium neomicrocephalum Lange-Bert. & F.Staab and Achnanthidium minutissimum (Kütz.) Czarn. were studied using light and scanning electron microscopy, and shape analysis. The type of Achnanthes microcephala f. scotica J.R.Carter (synonym: A. caledonica) and a population of A. neomicrocephalum from its type locality were investigated. Two new species, Achnanthidium tirolense sp. nov. and Achnanthidium lacuslustense sp. nov., found in two oligotrophic lakes in Germany and Austria, were described. Achnanthidium tirolense sp. nov. is distinguished by its rhombic-lanceolate valves with a slightly inflated valve centre and an acute-angled fascia on the raphe valve, and Achnanthidium lacuslustense sp. nov. by its large capitate poles, broad fascia on the raphe valve and strongly curved frustules. The distribution of A. caledonicum, A. sieminskae, A. neomicrocephalum and A. minutissimum in relation to land use and their species associations were investigated in 52 rivers, streams, and lakes of Scotland. Achnanthidium sieminskae, A. caledonicum, and A. neomicrocephalum were found in areas with low human impact where seminatural vegetation was dominant. The latter two species are typical in mountainous areas. In contrast, A. minutissimum sensu stricto was found in locations where human impact was greater. Although further data are required to determine which environmental variables underlie these distributions, our results suggest that the treatment of these species should be revised in ecological status assessments, and taxa aggregated under A. minutissimum sensu lato should be distinguished in ecological and biogeographical studies. [ABSTRACT FROM AUTHOR]

Приводятся результаты анализа литературных и оригинальных данных по экологии и географическому распространению 5 видов рода Eucocconeis P.T. Cleve во флоре водорослей Западной Сибири. Для каждого вида приводятся сведения по отношению к галобности, активной реакции воды, сапробности и географическому распространению.

A new freshwater species, Achnanthidium longissimum sp. nov., is described from Jiuzhai Valley, Sichuan Province (Southwest China), based on light and scanning electron microscopy. This species belongs to the 'Achnanthidium pyrenaicum complex', based on having transpically elongated areolae and deflected distal raphe fissures. Achnanthidium longissimum sp. nov. possesses a unique combination of features that includes having the longest valves in the genus (nearly 50 µm long), capitate ends, and raphe vestiges near the apices of the rapheless valve. Furthermore, the mantle has a single row of linear areolae, and a narrow hyaline area at the valve face - mantle junction on both valves. Achnanthidium longissimum is compared with morphologically similar species. The new species is known from epilithic and epiphytic collections from three alkaline lakes in Jiuzhai Valley. [ABSTRACT FROM AUTHOR]

A small marine benthic diatom pertaining to the order Achnanthales (Bacillariophyta) was observed from the Scattered Islands ('Eparses', Mozambique Channel, Indian Ocean) and from Napuka Atoll (North of the Tuamotu Archipelago, South Pacific). The latter taxon has unique characteristics (e.g., raphe valve striae composed of small areolae versus macroareolae on the sternum valve, low and plain mantle, simply hooked terminal raphe endings, high and complex cingulum composed of plain and open cingular bands, presence of a vestigial raphe) matching none of the genera split from Achnanthidium Kützing sensu lato (e.g., Planothidium Round & Bukhtiyarova, Karayevia Round & Bukhtiyarova ex Round, Psammothidium Bukhtiyarova & Round, Rossithidium Round & Bukhtiyarova), neither the new genus Madinithidium Witkowski, Desrosiers & Riaux-Gobin from which the striae of both valves are composed of macroareolae and the terminal raphe endings are doubly hooked. Pseudachnanthidium megapteropsis sp. nov and gen. nov is proposed. Due to its small size and to the fact that its striation is not discernible using light microscopy, the new taxon probably escaped the attention of taxonomists in the past. This taxon is found along with Madinithidium flexuistriatum that has close but distinctive morphology, clearly marked off under scanning electron microscope (SEM). Observation with a SEM is essential to differentiate the two latter small-celled and elusive taxa that have overlapping ecological niches. It remains unknown whether Pseudachnanthidium megapteropsis is a cosmopolitan-tropical taxon or if its environmental tolerance is wider. Two other small taxa possibly pertain to the same new genus: one from Reunion Island (Mascarene Archipelago, Indian Ocean) and the second from the Scattered Islands (Mozambique Channel). [ABSTRACT FROM AUTHOR]

O trabalho visa contribuir com o conhecimento da biodiversidade de diatomáceas no Estado de São Paulo e, particularmente, do gênero Lemnicola. Foram examinadas 96 amostras coletadas em 64 municípios distribuídos no Estado de São Paulo, incluindo materiais planctônicos e perifíticos de ambientes lóticos e lênticos. A única espécie do gênero, L. hungarica (Grunow) Round & Basson, foi documentada invariavelmente associada a superfícies submersas. Distribuiu-se em três municípios (Itapura, São Paulo e Reginópolis), indicando ter pequena distribuição no estado. O gênero é citado pioneiramente para o Estado de São Paulo, bem como são inéditas as descrições e ilustrações de características ultra-estruturais (MEV) para material brasileiro.