Cocconeis nosybetiana sp. nov. from Nosy Be Island (Madagascar) and allied taxa

International audienceCocconeis nosybetiana sp. nov. is described from Nosy Be Island (Madagascar, IndianOcean). This taxon is characterized by its sternum valve (SV) with ‘diabolo-like’ areolae (hymenes/supported by two transapical pegs), by its round valve shape and its raphe valve valvocopula(RVVC) with irregular short fimbriae and simple papillae. The raphe valve (RV) of the new taxonshares many similarities with that of Cocconeis scutellum Ehrenberg, except for its RVVC. Com-parison of the new species with allied taxa, particularly C. scutellum var. posidoniae f. decussata,is provided. In this case, the two taxa mainly differ in the structure of the SV areolae, which havean apical complete bar in place of transapical short pegs in C. nosybetiana. Furthermore, the shapeof the valve, the RV stria density, as well as the fimbriae and papillae of the RVVC are differentbetween the two latter taxa. The role of recent EM technologies on the morphological discrimina-tion of close taxa is discussed