Entomoneis vertebralis sp nov (Bacillariophyceae); a new species from hypersaline environments

A hyaline Entomoneis species was isolated during a study of microbial mats from hypersaline environments in the Exportadora de Sal salt works, Guerrer o Negro (Mexico). Morphological, ultrastructural and ecophysiological chara cteristics of the species were investigated. Live cells contained two plast ids. In girdle view the frustules appeared bilobate, deeply constricted, wi th a junction line visible only neat the central nodule. The margin of the wings was fibulate with 19-23 fibulae in 10 mu m, some of which, at irregul ar intervals, appeared longer and ended in small puncta. After mild cleanin g, neither valve body nor the sigmoid connecting bands appeared ornamented under the light microscope. Scanning electron microscopy revealed membranac eous valves without ornamentation and a strongly silicified fibulate keel. Furthermore, keels were the only part of the cell which could be found and recognized in cleaned field samples. This diatom species was able to grow o ver a salinity range of 15-50 parts per thousand and hence could be conside red a euryhaline marine species. (C) ADAC/Elsevier, Paris.