Leptochiton wui, Sirenko, 2018

Sirenko, Boris, 2018, Taiwanese deep-water chitons (Mollusca: Polyplacophora) and survey of chiton fauna of Taiwan, Zootaxa 4422 (3), pp. 301-344 : 322-325

Leptochiton wui n. sp.

( Figs 26–28 , 36B, C )

Type material. Holotype (MNHN IM-2000-33788) now disarticulated consisting of SEM stub of valves I, IV, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves.

Type locality. Taiwan, off Tashi, 24°35.1’N, 122°05.8’E, 221 m (Fishing Boat “ Chung Tung Long N26 ”, “ TAIWAN 2000”, stn CP58, 04.08.2000).

Etymology. Named in honour of Dr. Shi-Kuei Wu (UCM) who has studied chitons of Taiwan and Japan.

Material examined. Known only from the holotype.

Distribution. Near Taiwan, 221 m.

Diagnosis. Animal of small size, lowly elevated, valves carinated, not beaked, mucro of tail valve anterior, lateral areas of intermediate valves not raised, tegmentum of central areas of intermediate valves and antemucronal areas of tail valve sculptured with longitudinal rows of small granules, tegmentum of head valve, lateral and postmucronal areas sculptured with radial rows of small granules, each granule with 7–9 aesthetes, dorsal scales elongate sculptured with 7–9 longitudinal ribs, on one side, central teeth of radula rather long with straight sides, major lateral teeth with tridentate cusp, four gills on each side.

Description. Holotype (BL 6.5 mm) elongate oval in outline, shell carinated, low elevated in valve V (elevation ratio 0.34) not beaked, tegmentum white in color.

Head valve semicircular, posterior margin v-shaped, intermediate valves broadly rectangular with straight side slopes, anterior margin slightly emarginated, posterior margin straight, not beaked, lateral areas not raised, tail valve semicircular, narrower than head valve, mucro anterior, posterior slope almost straight.

Tegmentum finely granulose, head valve, lateral areas of intermediate valves and postmucronal area of tail valve sculptured with noticeable radial rows of granules, central area of intermediate valves and antemucronal area of tail valve sculptured with longitudinal rows of granules (42 rows in central area of intermediate valve), aesthete pores on each granule seven more often nine.

Articulamentum moderately developed, apophyses short, widely separated triangular in valves II–VII and trapezoidal in tail valve.

Girdle narrow, ca. 0.3 mm in width near valve V, densely clothed with elongated scales (53 x 21 µm) sculptured with 7–9 fine riblets, and interspersed with slender, smooth needles (102 x 10 µm). Intersegmental areas with longer scales (68 x 21 µm) of the same type as main dorsal armature, and long smooth needles (100 x 10 µm). Marginal needles of two kinds: long, smooth (85 x 10 µm) and ribbed (95 x 20 µm). Ventral side covered with imbricated, elongate, striated scales (60 x 19 µm), one row near outer margin occupied with larger scales (70 x 13 µm).

Four gills of equal size on each side, extending from valve VII to near anus.

Radula of the holotype 2.5 mm long with 31 transverse rows of mature teeth. Central teeth elongate, rectangular with straight side and narrow blade on top, head of major lateral teeth short, tricuspid, median denticle larger than others.

Gut contents containing cellulose woody material of brown colour.

Remarks. Leptochiton wui n. sp. forms a group with Leptochiton samadiae Sigwart & Sirenko, 2012 . Characteristics of this group are four gills, a radula with a central tooth that is elongate and rectangular with straight sides, tricuspid heads of major lateral teeth, dorsal scales with riblets on the dorsal side, and longitudinal rows of small granules in central area of intermediate valves and antemucronal area of tail valve.

Leptochiton wui n. sp. superficially strongly resembles Leptochiton samadiae and L. torishimensis ( Wu & Okutani, 1984) . Leptochiton wui n. sp. differs from L. samadiae by having dorsal scales with 7–9 riblets (vs. 4–5 in L. samadiae ), 7–9 aesthete pores in each granule (vs. 5 in L. samadiae ), radial rows of granules on the head valve, lateral areas of intermediate valves and antemucronal area of tail valve (vs. granules arranged in quincunx order in L. samadiae ).

The new species differs from L. torishimensis by having 4 gills on each side (vs. 10 gills in L. torishimensis ), head valve broader than tail valve (vs. head valve narrower than tail valve in L. torishimensis ), dorsal scales with 7–9 riblets (vs. 5–6 riblets in L. torishimensis ).

Figures

FIGURE 26. Leptосhitоn wui n.sp., holotype, Таiwаn, stn CP58, ВL 6.5 mm: А. Vаlve I, dorsаl view; В. Vаlve V, dorsаl view; C. Vаlve VIII, dorsаl view; D. Vаlve IV, ventrаl view; E. Vаlve V, detаil of tegmentum in centrаl аreа; F. Vаlve V, rostrаl view; G. Vаlve VIII, lаterаl view.

FIGURE 27. Leptосhitоn wui n.sp., holotype, Таiwаn, stn CP58, ВL 6.5 mm: А. Dorsаl scаles, mаrginаl needles аnd ventrаl scаles; В. Dorsаl scаles in suture; C. Dorsаl scаles; D. Rаdulа.

FIGURE 28. Leptосhitоn wui n.sp., holotype, Таiwаn, stn CP58, ВL 6.5 mm: А. Suturаl needle; В. Suturаl scаle; C. Dorsаl scаle; D. Ribbed mаrginаl needle; E. Smooth mаrginаl needle; F. Ventrаl scаle neаr mаrgin; G. Ventrаl scаle in centrаl pаrt; H. Heаd of mаjor lаterаl tooth of rаdulа; I. Centrаl аnd lаterаl teeth of rаdulа; J. Аesthete group in centrаl аreа. Scаle bаr 100 µm (А–I).

FIGURE 36. Complete specimens of species of genus Leptосhitоn: А. L. sp., Таiwаn, stn CP38, ВL 14 mm; В, C. L. wui. n. sp., holotype, Таiwаn, stn CP58, ВL 6.5 mm; D. L. lоngisetоsus, Таiwаn, stn CP38, ВL 8.5 mm; E, F. L. соnsimilis, Таiwаn, stn CP53, ВL 7.7 mm; G, H. L. bergenhayni, Таiwаn, stn CP81, ВL 7.5 mm; А, В, D, E, G. Dorsаl views. C, F, H. Lаterаl views. Scаle bаrs 2 mm.