Taxonomy and ecology of parasites on zooplankton, in particular, copepods

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The host-specificity, ultra-structure and life-cycle of the apostome ciliate Vampyrophyra pelagica parasitic on pelagic copepods were studied in the Seto Inland Sea. Completion of its life cycle usually needs feeding by invertebrate predators such as chaetognaths on copepods with phoronts of the ciliates. In contrast predation by fish larvae was not involved in it. Cilia of the ciliates are formed within the phoront, which guarantees quick excystation. Numerous thick membranes detected in the cytoplasm are considered to be precursors of food vacuole membranes of the trophont, and totally disappeared in the fully-grown cell. The morphology of the cytostome was newly revealed with SEM and TEM. Relationships between water temperature and duration of each stage of the ciliate were investigated in the laboratory. The maximum time from phoront hatching to tomite appearance at the lowest temperature (10℃) was nearly 20 times as long as the minimum time at the highest temperature (25℃), which seems to be caused by prolongation of the tomont. Apostome phoronts were broadly found from copepods collected from oceanic islands, deep-sea hyperbenthic layers, and brackish waters. This strongly suggests their paramount importance in marine food webs.A nicothoid copepod and an epicaridean isopod were newly described from the marsupium of the mysid Siriella okadai in the Seto Inland Sea. The maximum incidences of these parasites were up to 11 and 19 %, respectively. These parasites may compete severely with the same habitat and food.Intersex individuals of the shrimp Acetes sibogae and the mysid Siriella japonica izuensis were discovered, in the latter of which it seems to have been caused by infection of ellobiopsids. The occurrence of the dinoflagellate Oodinium inlandicum on pelagic chaetognaths in Korean and of the ellobiopsid Thalassomyces marsupii on the amphipod Scina vosseleri were also reported for the first time.