Leptochiton rissoi (Nierstrasz, 1905)

(Figs. 9–11)

Lepidopleurus rissoi Nierstrasz 1905: 6, figs 5, 52–55; Ferreira 1979: 163, figs 30–32.

Leptochiton rissoi; Kaas & Van Belle 1985: 110, fig. 48.

Type material. Lectotype, (RMNT) (designated by A. J. Ferreira, 1979).

Type locality. Celebes Sea, N of Manado, 3°27.1’N 125°18.7’E, 2053 m, Siboga St. 126 .

Material examined. Lectotype; Philippines, Sulu Sea, R / V Vitjaz, cruise 57, stn.7237, 7°39.9’– 7°31.1’N, 121°32.2’– 121°22.5’E, 4800 m, 21 spms (ZISP 2376) BL 9.0–16.0 mm, 28.02.1975.

Distribution. Indonesia (216-2053 m) and now Philippines (4800 m).

Remarks. This species is one of the largest of the genus (BL up to 40.0 mm) (Kaas & Van Belle 1985). The studied specimen is similar to the lectotype, which I have examined. Kaas & Van Belle (1985) gave a detailed description of the lectotype with drawings of the valves, armature of girdle and radula. However, there is a mistake in the description of the radula. The head of the major lateral tooth of the radula of the lectotype is not unidentate but bidentate. The Philippine specimen possesses 13 gills on each side arranged from valve VI to near the anus, and a radula that is 4.1 mm long with 53 transverse rows of mature teeth. Each granule of the tegmentum in the examined specimen has seven to nine pores of aesthetes. The lectotype has seven pores.

This species is most similar to L. vietnamensis, but differs in having granules in the central areas with seven to nine aesthete pores (vs. 18 to 21 pores in L. vietnamensis) and subcarinated valves (vs. usually rounded in L. vietnamensis). Moreover in L. rissoi, the granules on the longitudinal rows of the central areas are located at a small distance to each other; however they are very close to each other in L. vietnamensis).