Leptoplax unica (Nierstrasz, 1905)

(Figs 1-4)

Acanthochites (Notoplax) unicus Nierstrasz, 1905: 62, pl. 1 fig. 20, pl. 4, figs 115–117, pl. 5, fig. 118.

Leptoplax unica – Schwabe, 2006: 104, figs 1D, 6G-L, 8-10).

Type material. Holotype, ZMA 1899.05.07.

Type locality. Indone sia, 6°32’32’S, 120°25’34’’E, 8–10 m.

Material examined. South China Sea, Spratly Islands, 8°48’27’’N, 113°56’04’’E, 30 m, SCUBA, on old corals, 1 spm. ZIN 2572, BL 18 mm, 25.05.2019, leg. B. Sirenko.

Distribution. Indonesia, Papua New Guinea and Spratly Islands, 2– 30 m.

Remarks. It is a rarely collected species, with a total of 6 known specimens. The specimen studied here is the first found in the Spratly Islands. This specimen, as well as the type specimen from Indonesia and the specimen studied by Schwabe [2006] from New Guinea, has a large number of slits on the tail valve. Its slit formula is 5/1/9. It has 11 gills on each side arrange from valve V to valve VII. The radula of this specimen is 3.0 mm long with 32 transverse rows of mature teeth. Ventral spicules are flattened with one or two oblique, irregular riblets which arranged on a lower side of the spicule.