A FURTHER SEM STUDY OF MARINE BENTHIC DINOFLAGELLATES FROM A MANGROVEISLAND, TWIN CAYS, BELIZE, INCLUDING PLAGIODINIUM-BELIZEANUM GEN ET SP-NOV

This study indicates that bilaterally flattened, armored, benthic dino flagellates are more diverse in morphology than previously known. A ne w species, Plagiodinium belizeanum Faust et Balech gen. et sp. nov., i s described in floating detritus from Twin Cays, Belize, mangrove habi tats. Plagiodinium belizeanum cells are small, with dimensions of 26.5 -30.5 mum in length, 20-24.5 mum in width, and 6.5-8.5 mum in depth. C ells are oblong and bilaterally compressed with a posteriorly located, spherical nucleus, many chloroplasts, and spherical starch granules. The epitheca descends ventrally, is cap-shaped, and is composed of fiv e plates and a very small platelet provisionally named P(o) situated i n the center. The epitheca is narrowly oval in apical view with a poin ted truncated ventral side and a rounded dorsal side. The cingulum is composed of five plates. The hypotheca is constructed of five posterio rly elongated postcingular plates and one antapical plate. The sulcus is very short and narrow, comprised of five small plates. The thecal p late arrangement of P. belizeanum is P(o), 5', O'', 5C, 5''', 1'''', 5 C. No lists are present. Thecal plates have a smooth surface with smal l and irregularly scattered pores. The intercalary band is smooth on t he outer cell surface and broadly striated on its inner surface. We co nclude that P. belizeanum represents a new, benthic, peridinioid, armo red genus, Plagiodinium gen. nov. The taxonomic position of P. belizea num sp. nov. is compared to related sand-dwelling and bilaterally flat tened benthic dinoflagellates.