MORPHOLOGY AND ECOLOGY OF THE MARINE DINOFLAGELLATE OSTREOPSIS-LABENSSP-NOV (DINOPHYCEAE)

A new species, Ostreopsis labens Faust et Morton sp. nov., is describe d from three marine habitats: lagoonal water and Lagoonal sand from th e barrier reef of Belize, and associated with macroalgae from coral re ef habitats of Oshigaki and Iriomote Islands, Japan. Dimensions of Ost reopsis labens cells are 60-86 mu m long, 70-80 mu m wide, and 81-110 mu m in dorsoventral depth. Cells are broadly ovoid, anterioposteriorl y compressed bearing a spherical nucleus and many chloroplasts. The ep itheca is convex and composed of three apical plates, seven precingula r plates, and an apical pore plate. The cingulum is composed of six pl ates. The hypotheca is constructed of five posticugular plates, one po sterior intercalary and two antapical plates. The sulcus is small, rec essed, and hidden and exhibits a ventral pore and a ridged, curved pla te. The thecal arrangement of O. labens is P-o, 3', 7 '' 6C, 6S(?), V- p, R(p), 5, 1p, 2 ''''. Only one sulcal list is present. The thecal pl ates have a smooth surface with distinct round pores. The intercalary band between the thecal plates is smooth. A row of marginal pores line the lipped cingulum. Ostreopsis species are anteroposteriorly flatten ed, photosynthetic, benthic dinoflagellates that are more diverse in e cology than previously known. Ostreopsis labens is capable of living i n three, marine habitats: in the water column, in sand, and on macroal gal surfaces. It was most numerous in sand and less in lagoonal waters , and only a few cells were associated with macroalgae. Light and scan ning electron microscopy studies revealed engulfed cells within O. lab ens, which indicates mixotrophic/phagotrophic behavior. A ventral open ing situated in the cinglum of O. labens exhibits size variability; It may serve as an opening for engulfing food particles because it varie s in size. We propose that ingestion of prey by O. labens occurs throu gh the ventral opening the proposed feeding apparatus of this species, which is similar to the function of the peduncle-bike structure of mi xotrophic dinoflagellates. The behavior of O. labens appears similar t o that previously described for Dinophysis species.