Aspidisca major (Madsen, 1931) Kahl, 1932

1. Aspidisca major (Madsen, 1931) Kahl, 1932 View in CoL ( Fig. 1 View Fig )

Material examined. Marine water (salinity 37.8‰, temperature 18.3℃) collected from Sodol beach, Jumun-ri , Jumunjin-eup , Gangneung-si, Gangwon-do, Korea (37° 54 ʹ 24.6 ʺ N, 128°49 ʹ 41.7 ʺ E) on May 15, 2023 GoogleMaps .

Diagnosis. Size 76-78 × 42-49 μm after protargol impregnation (n = 3); body bean-shaped; cortex rigid; peristomial spur and projections along left margin on ventral side lacking ( Fig. 1A View Fig ); anterior adoral zone of membranelles (AZM1) about 4 μm long with 4 membranelles, posterior adoral zone of membranelles (AZM2) about 24 μm long after protargol impregnation and with 15- 18 membranelles; invariably seven frontoventral cirri in “ polystyla -arrangement”; five transverse cirri, cilia of each transverse cirrus not separated ( Fig. 1A View Fig ); four dorsal kineties with 25-28, 18-22, 19-23, and 22-24 dikinetids in dorsal kineties 1-4, respectively ( Fig. 1B View Fig ); dorsal kinety 1 distinctly curved to right posteriorly and ends near posterior end of dorsal kinety 2 ( Fig. 1C View Fig ); two ellipsoid macronuclei, micronucleus not observed ( Fig. 1D View Fig ).

Distribution. Germany, South Korea

Remarks. The Korean population of Aspidisca major corresponds with the German population redescribed by Kahl (1932) in all available aspects. Aspidisca major is a special species among the congeners in having two macronuclei ( Fig. 1D View Fig ). Because of this feature, A. major , A. binucleata Kahl, 1932 , A. fusca Kahl, 1928 , and A. mutans Kahl, 1932 can be easily distinguished from other members of the genus Aspidisca . However, A. major differs from A. binucleata in the number of frontoventral cirri (7 vs. 9). Aspidisca mutans differs from A. major by the number of frontoventral cirri (12 vs. 7) and the number of transverse cirri (7 vs. 5) ( Kahl, 1932). Aspidisca fusca differs from A. major by the presence of a peristomial spur (present vs. absent) ( Wu and Curds, 1979). Considering the arrangement of frontoventral cirri, number of membranelles in AZM1 and the presence of peristomial spur, the Korean population of A. major is similar to A. steini however, they differ mainly in the number of macronuclei (two vs. one) and larger body size (76-78 × 42-49 μm vs. 20-35 × 15-27 μm) ( Wu and Curds, 1979; Song and Wilbert, 1997).

Voucher slides. Two slides with protargol-impregnated specimens were deposited at the National Marine Biodiversity Institute of Korea (MABIK PR00045067, MABIK PR00045068).