Leptochiton mutschkeae, Sirenko, Boris, 2015

Sirenko, Boris, 2015, Shallow and deep-sea chitons of the genus Leptochiton Gray, 1847 (Mollusca: Polyplacophora: Lepidopleurida) from Peruvian and Chilean waters, Zootaxa 4033 (2), pp. 151-202 : 195-197

Leptochiton mutschkeae n. sp.

( Figs 40–42 )

Types. Holotype (ZISP 2214), now disarticulated consisting of SEM stub of valves I, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, and 6 paratypes ZISP (2215–2220).

Type locality. Peru-Chile Trench, RV Akademik Kurchatov, cruise 4, st. 241, 23°50’0’’S, 70°56’6’’W, 2900 m.

Etymology. Named after Dr. Erika Mutschke, Instituto de la Patagonia de la Universidad de Magallanes, Punta Arenas, Chile, who supported my field trip to Chile in 2000.

Material examined. Peru-Chile Trench, RV Akademik Kurchatov, cruise 4, st. 237, 23°19’5’’S, 70°57’1’’W, 3840 m, 1 paratype, BL— 27 mm, 30.09.1968; st. 239, 23°50’6’’S, 71°06’7’’W, 4550 m, 1 paratype, BL— 16 mm, 28.09.1968; st. 239’, 23°51’0’’S, 71°00’0’’W, 3960 m, 1 paratype, BL— 26 mm, 29.09.1968; type locality, holotype, BL—14.0 mm, and 1 paratype, BL—17.0 mm, 24.09.1968; st. 271, 17°42’0’’S, 78°59’0’’W, 3080– 2710 m, 1 paratype, BL— 17 mm, 20.10.1968.

Distribution. Peru-Chile Trench, 2900–4550 m.

Diagnosis. Animal moderate size. Shell low and carinated. Tail valve slightly wider than head valve. Mucro subcentral and vague. Tegmentum with distinctive, elongate, raised granules arranged quincuncially. Distance between granules nearly equal to width of granule. Each granule with one megalaesthete and four micraesthetes in front. Dorsal scales with two weak riblets. Central teeth of radula elongate with angular tip, major lateral teeth with unidentate cusp.

Eleven gills per side arranged from valve VI to anus.

Description. Holotype 17.0 x 7.7 mm BL, elongate oval in outline. Valves carinated, moderately elevated (elevation ratio 0.40 in valve V), not beaked. Color of tegmentum white. Head valve semicircular, slightly narrower than tail valve. Intermediate valves rectangular, tapering towards sides, lateral areas not raised, side slopes nearly straight. Tail valve with indistinct central mucro, antemucronal slope slightly convex, postmucronal slope straight.

Tegmentum uniformly sculptured with elongate-oval, raised quincuncially arranged granules, distance between granules nearly equal to width of granule. Each granule with one megalaesthete and four micraesthetes in front, aesthete group located at granule’s front part.

Articulamentum well developed, apophyses small, widely separated, subtriangular in valves II–VII, more or less trapezoidal in tail valve.

Girdle narrow (about 0.6 mm near valve V, 8% of total width), dorsally covered with elongate, sharply pointed scales (90 x 30 µm) sculptured with two very week riblets, sutural needles smooth (196 x 21 µm), dorsal needles (190 x 20 µm) smooth, randomly scattered between scales. Marginal needles up to 200 x 19 µm, smooth. Ventral scales lanceolate, flat, smooth (100 x 23 µm).

Radula of holotype 6.3 mm long with 28 transverse rows of mature teeth, central teeth elongate with angular tip, major lateral teeth with unidentate cusp.

There are eleven gills per side extending from valve VII to anus.

Remarks. Leptochiton mutschkeae n. sp. belongs to the L. belknapi group and superficially resembles L. belknapi , L. japonicus , L. alveolus , L. giganteus , L. macleani and L. sigwartae . Leptochiton mutschkeae differs from L. macleani in having five pores in the aesthete group (three pores in L. macleani ), two ribs on the dorsal scales (one rib in L. macleani ) and a straight postmucronal slope (convex in L. macleani ). Leptochiton mutschkeae differs from L. sigwartae in having a vague mucro (distinct mucro in L. sigwartae ), a tail valve narrower than the head valve (wider in L. sigwartae ) and a moderately elevated shell (highly elevated in L. sigwartae ). Leptochiton mutschkeae differs from L. belknapi in having a vague mucro (distinct mucro in L. belknapi ), five pores in the aesthete group (three pores in L. belknapi ), an unidentate cusp of the major lateral tooth (large outer and small inner denticle in L. belknapi ) and a straight postmucronal slope (concave in L. belknapi ). Leptochiton mutschkeae n. sp. differs from L. japonicus , L. alveolus and L. giganteus in having a vague mucro (distinct mucro in the three mentioned species). Leptochiton mutschkeae differs from L. japonicus in having two ribs on the dorsal scales (6–8 ribs in L. japonicus ). Leptochiton mutschkeae differs from L. alveolus by having a shorter antemucronal area, a narrower jugal sinus and by lacking an additional denticle on the cusp of the major lateral teeth of the radula. Leptochiton mutschkeae differs from L. giganteus in having a shorter antemucronal area, two ribs on the dorsal scales ( L. giganteus lacks ribs on the scales) and wider jugal sinus.

Figures

FIGURE 40. Leptochiton mutschkeae n. sp. Holotype, (ZISP 2214). Peru-Chile Trench, RV Akademik Kurchatov, st. 241, BL— 14.0 mm. A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Valve VIII, detail of tegmentum surface; E. Valve V, detail of tegmentum surface of central area; F. Valve VIII, lateral view; G. Valve V, rostral view.

FIGURE 41. Leptochiton mutschkeae n. sp. Holotype, (ZISP 2214). Peru-Chile Trench, RV Akademik Kurchatov, st. 241, BL— 14.0 mm. A, C. Dorsal, marginal and ventral scales and needles; B. Dorsal scales in intersegmental area; D. Central portion of radula.

FIGURE 42. Leptochiton mutschkeae n. sp. Holotype, (ZISP 2214). Peru-Chile Trench, RV Akademik Kurchatov, st. 241, BL— 14.0 mm. A. Sutural needle; B. Dorsal scale; C. Dorsal needle; D. Marginal needle; E. Ventral scale; F. Central and first lateral teeth of radula G. Heads of major lateral tooth; H. Aesthete group in central area. Scale bar 100 µm (A – G).