OBSERVATIONS ON THE THECA OF THE MOTILE PHASE OF FREE-LIVING AND SYMBIOTIC ISOLATES OF ZOOXANTHELLA-MICROADRIATICA (FREUDENTHAL) COMB NOV

A strain of Zooxanthella microadriatica (Freudenthal) comb.nov. has been isolated from decaying Chondrus crispus (L.) Stackh. The ultrastructure of this isolate has been compared to that of Z. microadriatica inhabiting Cassiopea Peron & Lesueur, 1809, sp. In an aqueous medium the cell cycle of both isolates consists of a coccoid non-motile phase alternating with a thecate motile phase. A smooth unornamented wall surrounds the non-motile phase. The motile phase has an amphiesma consisting of an outer membrane and a layer of overlapping thecal vesicles located above an irregular system of vacuoles which enclose the organelle bearing cytoplasm. The thecal plates are unornamented except for scattered perforations. Material of unknown composition extruded from the cells may be released through the pores. A pellicular layer is absent. The thecal plates are arranged in a recognizable pattern. The epitheca has a thick suture homologous to the acrobase of nonthecate species. The cingulum is composed of a double row of thecal plates. A peduncle is located between the emergence of the two flagella. The systematics of genera proposed for dinoflagellates symbiotic with animals is discussed and Symbiodinium Freudenthal is placed in synonymy of Zooxanthella Brandt. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.