Leptochiton clarki, Sigwart, Julia D. & Sirenko, Boris I., 2012

Sigwart, Julia D. & Sirenko, Boris I., 2012, Deep-sea chitons from sunken wood in the West Pacific (Mollusca: Polyplacophora: Lepidopleurida): taxonomy, distribution, and seven new species, Zootaxa 3195, pp. 1-38 : 22-23

Leptochiton clarki n. sp.

Figures 4 F, 15, 16

Type material. Holotype ( MNHN 23701) disarticulated, consisting of mounts of shell, perinotum and radula, 5 paratypes ( MNHN 23702) and 1 paratype ( ZISP).

Type locality. Solomon Island, 9°10.4'S, 159°53'E, 749–799 m; Salomon 1 sta. CP1751.

Etymology. Named after Roger Clark, of the Santa Barbara Museum of Natural History, USA, who is a specialist on eastern Pacific chitons.

Material examined. 14 specimens in 5 lots from the Solomon Islands.

Distribution. Off Solomon Islands, 305–1135 m. Found living and feeding on sunken terrestrial plant remains.

Diagnosis. Animal small, up to 10.5 mm, valves white, carinated, not beaked, tail valve with subcentral mucro. Tegmentum sculptured with oval raised granules, arranged quincuncially each granule with 1 megalaesthete and 4 micraesthetes in front. Girdle covered with elongate bluntly pointed scales, intersegmental and marginal bristles up to 450 μm. Major lateral teeth with three sharp cusps. Four gills on each side.

Description. Holotype 8.0 × 4.2 mm. Shell carinated, elevated (dorsal elevation ratio 0.43) not beaked. Head valve semicircular anterior slope straight. Intermediate valves short, lateral areas slightly depressed near apex, anterior margin jugally slightly excavated, side margins somewhat rounded, posterior margin straight, apices in conspicuous, side slopes evenly, rounded. Tail valve slightly smaller than head valve, with subcentral mucro, anterior margin produced, between the apophyses, posterior margin evenly rounded, postmucronal slope slightly concave. Tegmentum sculptured with raised oval granules (51 μm) arranged in quincunx throughout, except for pleural areas where granules arranged in several longitudinal rows, slightly diverging posteriorly. Each granule with 1 megalaesthete and 4 micraesthetes in front. Colour of tegmentum white older parts of valves covered with black deposit.

Articulamentum weekly developed; apophyses wide apart, narrowly triangular in intermediate valves, jugal sinus rather wide.

Girdle narrow relative to valves, about 0.5 mm wide near valve V, dorsally densely clothed with elongate bluntly pointed scales 100 × 25 μm. Intersegmental areas with 3–4 chitinous bristles (up to 450 μm), the same type of long bristles found in the marginal fringe (most numerous in the posterior region of the animal). Each bristle with small spicule up to 60 μm at distal end. Marginal fringe also with scanty spines (up to 100 μm). Ventral side (hyponotum) clothed with pointed scales 67–70 × 21–23 μm.

Radula of holotype 2.7 mm long, with 35 transverse rows of mature teeth. Central tooth is short with a rounded 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. Leptochiton clarki bears a close resemblance to L. dykei , L. vitjazi , L. vanbellei , L. deforgesi and L. thandari . It differs from the four latter species by having long intersegmental and marginal chitinous bristles. The new species has four micraesthetes in each aesthete group whereas L. vitjazi and L. vanbellei have only two micraesthetes per megalaesthete. Leptochiton clarki differs from L. dykei in having shorter intersegmental chitinous bristles (450 and 1000 μm respectively); higher dorsal elevation (0.43 in L. clarki and 0.30 in L. dykei ); smaller granules of tegmentum (51 and 70 μm, respectively), and in L. clarki the interstices between longitudinal rows of granules on pleural areas are smaller.

Figures

FIGURE 4. Preserved specimens of the seven new species described. In all pictures, anterior is at top and scale bars are 1 mm. A. Leptochiton consimilis n. sp., lateral view of right side, Solomon Islands, Salomon 2 sta. CP 2216. B. Leptochiton angustidens n. sp., lateral view of right side (at left) and dorsal view (at right). Specimen is from Vanuatu, Boa 1 sta. CP 2432. C. Leptochiton dykei n. sp., lateral view of right side (at left) and dorsal view (at right), Vanuatu, Boa 1 sta. CP 2412. D. Leptochiton samadiae n. sp., lateral view of right side (at left) and dorsal view (at right), Solomon Islands, Salomon 2 sta. CP 2285. E. Leptochiton longisetosus n. sp., lateral view of right side (at left), Vanuatu, Boa 1 sta. CP 2422. F. Leptochiton clarki n. sp., paratype, lateral view, Solomon Islands, Salomon 1 sta. CP 1751. G. Leptochiton schwabei n. sp., paratypes, right lateral view (at left), and dorsal view (at right) in different specimens, both from Solomon Islands, Salomon 1 sta. CP 1783.