Onithochiton stracki Sirenko, 2012 .

(Figs 3E, 16–18)

Onithochiton stracki Sirenko 2012: 85, pl. 13 B, figs 25, 26.

Type material. Holotype (ZISP 2175).

Type locality. South China Sea, off South Vietnam, Nhatrang Bay, Nok Island .

Material examined. South China Sea, China, Hainan Island. Xincun, sample 1, 1 spm, BL 17.0 mm, 19.04.1958, leg. O. Scarlato; stn 22, 18°11’46’’N, 109°29’40’’E, depth 2 m, on old corals, 1 spm, BL 5.0 mm, 21.11.2016, leg B. Sirenko; stn 26, 18°11’46’’N, 109°29’40’’E, intertidal–1.5 m, on stones, 3 spms, BL 3.0–12.0 mm, 22.11.2016, leg. B. Sirenko, S. Grebelniy.

Distribution. South China Sea, Vietnam from Phu Quy Island to Danang and Hainan.

Remarks. The studied specimen (BL 11.0 mm) has a radula 3.4 mm long with 36 transverse rows of mature teeth and 11 gills extended from valve II to valve VII. The slit formula of this specimen is 8/1/0. Specimens of this species from Hainan Island differ from Onithochiton hirasei from Guangdong Province by having a coarser sculpture of the tegmentum and larger spicules of girdle. This is the first find of O. stracki from Hainan Island.