Resting stages in the genus Bysmatrum.

The genus Bysmatrum Faust & Steidinger was erected in 1998 for three peridinoid red tide forming dinoflagellates previously placed in the genus Scrippsiella and Peridinium. Other two species were later described, B. teres and B. granulosum. This genus includes typical benthic sand-dwelling species that occur in tide pools and in sandy sediments. They are also epibiotic on macroalgae or corals. Bysmatrum species are reported from warm temperate, tropical and subtropical areas. Species belonging to this genus have not been reported so far in the Mediterranean basin. Nowadays, the life cycle of these species is not described and reproduction type is not well known, as well as any data on genetic aspect are available. Cultures established from two different cyst morphotypes isolated from the sediment of Fangar Bay (Ebre Delta, NW Mediterranean Sea) were attributed to a species of the genus Bysmatrum. The vegetative cells are 32.2- 39.7 μm long and 32.2-39.7 μm wide. They show the typical plate pattern of the genus (Po, X, 4', 3a, 7'', 6c, 4s, 5''', 2'''') with the second and third anterior intercalary plates not in contact with one another. First phylogenetic data for this genus were obtained. The dif- ferent morphology of the two progenitor morphotypes suggests the possibility of different sexual routes in the life cycle of this species.