Metaurostylopsis rubra Song and Wilbert 2002

2. Metaurostylopsis rubra Song and Wilbert, 2002 (Fig. 2) Material examined. Marine water (salinity 36.1‰, temperature 16.8℃) collected from Sanyang-eup, Tongyeong-si, Gyeongsangnam-do, South Korea (34°49 ʹ 16 ʺ N, 128°26 ʹ 27 ʺ E) on April 17, 2023. Diagnosis. Size 68-77 × 49-58 μm after protargol impregnation (n = 3); body oval to ellipsoidal with brick-reddish color; body flexible and slightly contractile; adoral zone of membranelles occupies about 50% of body length; 36-44 adoral membranelles; 1 buccal cirrus; 3 frontal, 8-9 frontoterminal, and 5-6 transverse cirri; 13- 16 midventral pairs and a midventral row with about 8-12 cirri, extending to the midline of body; 10-12 left and 6-7 right marginal rows (Fig. 2A); three dorsal kineties (Fig. 2B); and about 70 macronuclear nodules. Distribution. Antarctic, South Korea Remarks. The Korean population of Metaurostylopsis rubra is similar to the type population of M. rubra described by Song and Wilbert (2002) in most features except for the slightly non-overlapping number of midventral pairs (13-16 vs. 8-11) and left marginal rows (10- 12 vs. 6-9) (Song and Wilbert, 2002). Metaurostylopsis rubra can be easily distinguished from other congeners by the cell color and the number of midventral pairs and left marginal rows (Fig. 2A). Since the number of living cells were not enough to examine in detail, we cannot determine whether the reddish color of the cells is due to the reddish cytoplasm or the cortical granules. Among the congeners, there is no species with more than six right marginal rows (Song et al., 2020). Also, only two species, M. struederkypkeae and M. parastruederkypkeae Lu et al., 2016, have reddish body color like M. rubra, but they differ from the present Korean population by the number of right marginal rows (3 vs. 3-5 vs. 6-7) (Shao et al., 2008b; Lu et al., 2016; Song et al., 2020). Voucher slides. Two slides with protargol-impregnated specimens were deposited at the National Marine Biodiversity Institute of Korea (MABIK PR00045065, MABIK PR00045066).