Morphology and Infraciliature of a New Marine Ciliate Euplotidium smalli n. sp. with Description of a New Genus, Paraeuplotidium n. g. (Ciliophora, Euplotida)

The morphology and infraciliature of a new hypotrichous ciliate, Euplotidium smalli n. sp., isolated from eutrophic coastal water in Korea, were observed in living cells and investigated using the protargol impregnation technique. This new ciliate bears 13–14 frontoventral cirri, 7 transverse cirri, and 5–6 dorsal kinetics. Neither left marginal cirrus nor caudal cirrus is present. The new species differs from the related species, Euplotidium agitatum Noland, 1937 in the different number of frontoventral and transverse cirri and different body shape. With the exception of Euplotidium agitatum , the known species of the genus Euplotidium Noland, 1937 with the presence of left marginal cirrus are assigned to a new genus, Paraeuplotidium n. g. Diagnosis of Paraeuplotidium is: Gastrocirrhidae with funnel‐shaped buccal cavity; with frontoventral and transverse cirri; left marginal cirrus present. Paraeuplotidium itoi (Ito, 1958) n. comb. is designated here the type species. Four additional species are included: Paraeuplotidium psammophilus (Vacelet, 1961) n. comb., Paraeuplotidium arenarium (Magagnini & Nobili, 1964) n. comb., Paraeuplotidium helgae (Hartwig, 1980) n. comb., and Paraeuplotidium prosaltans (Tuffrau, 1985) n. comb. An improved generic diagnosis of Euplotidium is suggested based on morphology and infraciliature characters: marine hypotrichs with a funnel‐shaped buccal cavity; with frontoventral and transverse cirri; neither left marginal cirrus nor caudal cirri present.