Leptochiton schwabei Sigwart & Sirenko, 2012, n. sp.

Leptochiton schwabei n. sp.

Figures 4 G, 17, 18

Type material. Holotype (MNHN 23703) disarticulated, consisting of mounts of shell, perinotum and radula, 15 paratypes (MNHN 23704) and 1 paratype (ZISP).

Type locality. Solomon Islands, 8°32.8'S, 160°41.7'E, 399–700 m; Salomon 1 sta. CP1783.

Etymology. Named after Enrico Schwabe of the Zoologische Staatssammlung München (Germany), who is an expert on chitons and other molluscs.

Material examined. 4 specimens in 2 lots from Vanuate, 34 specimens in 7 lots from the Solomon Islands.

Distribution. Vanuatu (641 m, 900 m) and the Solomon Islands, 500– 839 m. Found living and feeding on sunken terrestrial plant remains.

Diagnosis. Animal small, up to 11.0 mm. Shell subcarinate, the sides weakly convex, valves not beaked, mucro of tail valve subcentral. Tegmentum sculptured with rounded, weakly raised granules arranged quincuncially throughout; each granule with 1 megalaesthete and 4 micraesthetes in front. Girdle densely covered with long scales with 3–4 ribs, long chitinous bristles with needle-like spines at their tip. Major lateral teeth of radula with tridentate cusps. Four equal gills on each side.

Description. Holotype 8.0 × 4.5 mm. Valves subcarinate, moderately elevated (dorsal elevation ratio 0.33 in valve II). Head valve semicircular. Intermediate valves rectangular, anterior margin slightly concave, posterior margin straight, sides rounded, apex not projecting. Tail valve as wide as head valve, mucro subcentral, posterior slope concave. Tegmentum sculptured with rounded slightly raised granules (56 μm) arranged quincuncially throughout. Each granule with 1 megalaesthete and 4 micraesthetes with caps protruding from aesthetes openings. Colour of tegmentum white, older parts of valves covered with black deposit near the apex.

Articulamentum white, weakly developed, apophyses narrow, triangular in the intermediate valves, trapezoidal in tail valve. Jugal sinus wide almost straight.

Girdle rather wide relative to valves, about 0.6 mm wide near valve V, dorsally densely covered with long scales (up to 57–60 × 12 μm) with 3–4 ribs. Intersegmental areas each with 3–4 long (up to 300 μm) chitinous bristles with needle-like spines (73–85 × 10 μm) at their tip. The same bristles in the marginal fringe, most numerous and longest in the posterior area of the animal. Marginal fringe also with occasional long spines (95 × 11 μm). Ventral side (hyponotum) clothed with pointed scales (62 × 15 μm).

Radula of holotype 3.2 mm long, with 40 transverse rows of mature teeth. Central tooth elongate with narrow blade, major lateral tooth with tricuspid dental cap.

Holotype with 4 equal gills on each side, extending from valve VII to near the anus.

Remarks. This new species is similar to L. longisetosus It differs from L. longisetosus by having caps protruding from the aesthetes openings, the form of its central radula tooth, and L. schwabei has more numerous micraesthetes in each aesthete group (four micraesthetes in L. schwabei and two micraesthetes per megalaesthete in L. longisetosus). Leptochiton schwabei differs from L. clarki also by having caps protruding from aesthetes openings, and the arrangement of granules on the valve pleural areas.