Bysmatrum granulosum sp. nov., a new benthic dinoflagellate from the southwestern Indian Ocean

A new benthic marine dino¯agellate, Bysmatrum granulosum Ten-Hage, Turquet, Quod & Couté, sp. nov., was obtained from sediment and coral samples from sites of La Réunion Island (SW Indian Ocean). This new species is described and illustrated by light and scanning electron micrographs. Cells are 40-50 µm long and 40-46 µm wide. The epitheca is conical and smaller than the hypotheca, which is trapezoidal with convex sides. Plate tabulation is typical for the genus (Pₒ, X, 4', 3a, 7'', 6c, 5s, 5''', 2''''); epithecal plates 3’ and 4’’ separate the intercalary plates 2a and 3a. Thecal plates are perforated by pores and covered by both small and minute wart-like projections, linearly arranged, radiating from the apical pore. This new species differs from the three others of the genus Bysmatrum in the following characters: cell shape and size, size of the apical pore complex and features of thecal plates (plate shapes and ornamentations

Phytoplankton of lentic waters from the campus of Santa Catarina University (Florianópolis, SC, Southern Brazil)

Phytoplankton of lentic waters from the Campus of Santa Catarina University (Florianópolis, SC, Southern Brazil). Phytoplankton of lentic waters from the Campus of Santa Catarina University was studied from September 1993 to March 1994 and September 1994 to March 1995, excepting the class Bacillariophyceae. Samples were taken from three ponds, namely Horto Botânico, Centro de Convivência and Hospital Universitário. Forty two genera were identified, including 78 species, verieties and formae. Cellular measurements, occurrence at the sampling stations and pictures are given for each infrageneric taxon. In general, species composition of the ponds changed slightly from one period to another. Chlorophyta was the richest taxonomic group in the three localities; among them, the order Chlorococcales, which often abounds in eutrophic waters, prevailed in richness and frequency of species. The majority of the identified taxa is widespread throughout the world.Fitoplâncton de águas lênticas do Campus da Universidade Federal de Santa Catarina (Florianópolis, SC, Brasil meridional). Estudou-se o fitoplâncton de águas lênticas do Campus da Universidade Federal de Santa Catarina, excetuando-se a Classe Bacillariophyceae, de setembro de 1993 a março de 1994 e de setembro de 1994 a março de 1995. As amostras foram coletadas em três estações, denominadas «lagos» do Horto Botânico, Centro de Convivência e Hospital Universitário. Identificaram-se 42 gêneros, incluindo 78 espécies, variedades e formas. Para cada táxon infragenérico são fornecidas as medidas celulares, ocorrência nas estações de coleta e ilustrações. Em geral, a composição florística dos corpos d'água apresentou poucas modificações de um período a outro. Chlorophyta mostrou a maior riqueza taxonômica nas três localidades; dentre as algas verdes, a Ordem Chlorococcales, normalmente abundante em águas eutróficas, predominou em riqueza e freqüência de espécies. A maioria dos táxons identificados é cosmopolita

Voronoi Growth Model of Sheet Nacre.

The aim of this work was to study the tiling mode of nacre tablets in the 'brick and mortar' array of sheet nacre. For that purpose, incipient shell nacre (Pinctada margaritifera) was analysed by electron microscopy (SEM) and Raman spectroscopy. Experimental observations pointed out the key role of the stairs-like growing front in sheet-like nacre not only for its long range ordering but also as controlling the hierarchy of local mechanisms. A morphogenesis sequence is proposed taking into account the dynamics of the environment. First, the mantel cells are organised to synthesise and discharge alternatively the extrapallial fluid as batches. Because of the stairs-like feature of the growth front, the extrapallial fluid organizes as successive 'biological films', each of them delayed from the underlying one by 10 to 15µm. Each film is a compartment to prefigure a nacre layer. Then, after individualisation, this film undergoes nucleation and crystallisation of tablets. Finally, the biological film transforms progressively as mature nacre following self assembly mechanisms. The resulting tablets have a shape which responds to a Voronoi growth model, this is shown for the first time: aggregation at the same speed in all directions around single growth centers. This is an efficient model to understand the growth mechanism and rationalise all the experimental observations we have obtained

Sheet nacre growth mechanism: a Voronoi model.

Xavier Bourrat is in ISTO's lab since January 2005International audienceShell nacre (mother of pearl) of Pinctada margaritifera was analyzed by scanning electron microscopy. The originality of this work concerns the sampling performed to observe incipient nacre on the mantle side. The whole animal is embedded in methyl methacrylate followed by separation of the shell from the hardened mantle. It is revealed this way how each future nacre layer pre-exists as a film or compartment. Experimental observations also show for the first time, the progressive lateral crystallization inside this film, finishing under the form of a non-periodic pattern of polygonal tablets of bio-aragonite. It is evidenced that nuclei appear in the film in the vicinity of the zone where aragonite tablets of the underlying layer get in contact to each other. A possible explanation is given to show how nucleation is probably launched in time and space by a signal coming from the underlying layer. Finally, it is evidenced that tablets form a Voronoi tiling of the space: this suggests that their growth is controlled by an "aggregation-like" process of "crystallites" and not directly by the aragonite lattice growth

An extremely radioresistant green eukaryote for radionuclide bio-decontamination in the nuclear industry

International audienceNuclear activities generate radioactive elements which require processes for their decontamination. Although biological remediation has proved efficient in industrial applications, no biotechnology solution is currently operational for highly radioactive media. Such a solution requires organisms that accumulate radionuclides while withstanding radioactivity. This paper describes the potentialities of an extremophile autotrophic eukaryote, Coccomyxa actinabiotis nov. sp., that we isolated from a nuclear facility and which withstands huge ionizing radiation doses, up to 20,000 Gy. Half the population survives 10,000 Gy, which is comparable to the hyper-radioresistant wellknown prokaryote Deinococcus radiodurans. Cell metabolic profile investigated by nuclear magnetic resonance was hardly affected by radiation doses of up to 10,000 Gy. Cellular functioning completely recovered within a few days. This outstanding microalga also strongly accumulates radionuclides, including 238U, 137Cs, 110mAg, 60Co, 54Mn, 65Zn, and 14C (decontamination above 85% in 24 h, concentration factor, 1,000-450,000 mL g-1 fresh weight). In 1 h, the microalga revealed as effective as the conventional physico-chemical ion-exchangers to purify nuclear effluents. Using this organism, an efficient real-scale radionuclide bio-decontamination process was performed in a nuclear fuel storage pool with an important reduction of waste volume compared to the usual physico-chemical process. The feasibility of new decontamination solutions for the nuclear industry and for environmental clean-up operations is demonstrated

Some taxonomical and nomenclatural changes in the genus Trachelomonas Ehrenb. emend. Defl. (Euglenophyta)

This paper deals with the taxonomic and nomenclatural revision of some species and infraspecific taxa of the genus Trachelomonas (Euglenophyceae). Twelve changes are suggested. Among them, we propose new synonyms for the following four taxa: Trachelomonas acanthophora var. minor Balech et Dastugue, T. acanthophora var. speciosa (Defl.) Balech, T. hispida (Perty) Stein emend. Defl. and T. superba var. swirenkiana Defl.; the identification of an unnamed but previously illustrated and described individual: T. amphoriformis var. granulosa Couté et Iltis; a new variety: T. megalacantha da Cunha var. paucispina Couté et Tell, and five new status and new combinations: T. crateriphora (Conforti et Ruiz) Couté et Tell, T. duplex (Defl.) Couté et Tell, T. rugulosa var. paralella fo. paralella (Tell et Zalocar) Couté et Tell and T. rugulosa var. paralella fo. minima (Conforti et Ruiz) Couté et Tell.Fil: Couté, Alain. Museum National D'histoire Naturelle; FranciaFil: Tell, Hector Guillermo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin