3 NEW SPECIES AND A NEW RECORD OF CHAETOPHORACEAN (CHLOROPHYTA) ALGAEFROM TERRESTRIAL HABITATS IN ANTARCTICA

Descriptions are provided of cultured isolates of four species of chlo rophyte microalgae which would traditionally be assigned to the Chaeto phoraceae, Leptosiroideae (sensu Bourrelly, 1990). Light microscope ob servations are supplemented by electron microscopy, particularly of py renoid features. Three new species are described: Coccobotrys mucosus sp. nov., Dilabifilum prostratum sp. nov. and Desmococcus endolithicus sp. nov. Desmococcus olivaceus is a new record for Antarctica. Diagno stic features of the new species include extensive gelatinisation of c ell walls in old cultures of C. mucosus, growth of a well-developed ps eudoparenchymatous prostrate system in liquid cultures of D. prostratu m, and production of quadriflagellate zoospores by D. endolithicus whi ch is a new observation for this genus. Unusual and contrasting ultras tructural features of the pyrenoid are described for D. prostratum and the Desmococcus species. The former is traversed by appressed pairs o f thylakoids coated with pyrenoglobuli; the latter is traversed by sin gle thylakoids with pyrenoglobuli surrounding the pyrenoid matrix.