Euplotes orientalis Jiang 2010

3. Euplotes orientalis Jiang et al., 2010 Material examined. Marine water (salinity 34‰) collected from Udo-myeon, Jeju-si, Jeju-do, Korea (33°29 ʹ 47 ʺ N, 126°57 ʹ 59 ʺ E) on May 29, 2024. Diagnosis. Body size 32.1-34.3 × 15.5-17.9 μm after silver nitrate impregnation (n = 5), shape rotund; 21-23 adoral membranelles; 10 frontoventral (including 2 nonciliated reduced cirri), 5 transverse, 2 caudal and 2 marginal cirri (Fig. 3A). 7 dorsal kineties with 6 or 7 dikinetids in the middle one; dorsal argyrome pattern of doublepatella -I type (Fig. 3B). Distribution. China (Jiang et al., 2010) and Korea (present study). Remarks. The Korean population corresponds well with the Chinese type population described by Jiang et al. (2010) in several characteristics: body size after silver impregnation (32.1-34.3 μm vs. 32-42 μm); number of adoral membranelles (21-23 vs. 18-25), frontoventral cirri (8 vs. 8), caudal cirri (2 vs. 2), marginal cirri (2 vs. 2), dorsal kineties (7 vs. 6 or 7), dikinetids in the mid-dorsal row (6 or 7 vs. 6-8); dorsal argyrome pattern (double- patella -I); and habitat (marine). Among the approximately 160 congeners, the presence of a reduced cirrus is a unique feature, with only eight species exhibiting this trait (Do et al., 2024). Of these species, Euplotes raikovi Agamaliev, 1966 is similar to E. orientalis but can be distinguished by the number of frontoventral cirri (7 vs. 8) and reduced cirri (1 vs. 2). Euplotes pseudoraikovi Alekperov, 2005 also resembles E. orientalis, but differs in the number of frontoventral cirri (8 vs. 6). Voucher slides. Four slides with silver nitrate-impregnated specimens (MABIK PR00045072-PR00045075) were deposited at the National Marine Biodiversity Institute of Korea.