Crepidoodinium australe n. sp., an ectoparasitic dinoflagellate, is described from the gills of Sillago cjliata (sand whiting) from the coast of New South Wales, Australia. Large, flat trophonts with a pointed apex, up to 820 X 235 pm in size, are attached to the gill filaments. Grown trophonts detach from the host, sink to the bottom, round up, and secrete a cyst envelope. Inside, the trophont divides into dinospores of Gyrod~niurn type, 17 X 12 pm, which migrate to new hosts. C. australe differs in morphology, hosts and area of distribution from C. cyprinodontum, the only species known of the genus. C. australe is ectocommensal. It has a strongly developed plastid system and is attached to the surface of the epithelial cells of the gills by means of tiny cytoplasmic projections, rhizoids. Thus a firm adherence to the host is ensured. However, no obvious injury is inflicted upon the host cells. C. australe is characterized by numerous pits in the surface theca, on the bottom of which are clusters of cisternae, each cluster being comparable to a small pusular system. The large nucleus of the trophont lacks condensed interphase chromosomes and reveals a n internal network of canalicules representing numerous invaginations of the nuclear envelope.
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Lom et al. (1993) studied this question.