Craspedostauros gen. nov., a new diatom genus for some unusual marine raphid species previously placed in Stauroneis Ehrenberg and Stauronella Mereschkowsky

Based on light and electron microscopical investigations, a new genus Crasp edostauros is described for a group of marine biraphid diatoms previously p laced in Stauroneis Ehrenberg. The genus Stauronella Mereschkowsky had been erected for one of these species, Amphiprora constricta sensu W. Smith, bu t Mereschkowsky's name cannot be used for nomenclatural reasons. Craspedost auros species can be recognized by the possession of cribrate areolae, a st auros that is usually narrower than the fascia, many girdle bands with doub le rows of cribrate areolae and two chloroplasts, fore and aft of the centr al cytoplasm, each with a central pyrenoid. The genus shows similarities in its pore structure and chloroplast type and arrangement to Mastogloia Thwa ites ex W. Smith and Aneumastus Mann & Stickle, suggesting that it is more closely related to these than to other naviculoid genera with a stauros, i. e. Stauroneis, Staurophora Mereschkowsky, Meuniera Silva and Haslea Simonse n. The stauros is a feature that probably arose a number of times. A descri ption of the genus and its currently recognized members is given, with a ke y to their identification. Four new species are described, the types of whi ch have been deposited in the Natural History Museum, London. The status of Stauronella constricta var, linearis Mereschkowsky remains unclear in the absence of any material from the Black Sea. Some marine stauroneid diatoms that do not belong in Craspedostauros are briefly discussed.