Leptochiton macleani, 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 : 188-190

Leptochiton macleani n. sp.

( Figs 34–36 )

Types. Holotype (ZISP 2221), now disarticulated consisting of SEM stub of valves I, V, VI, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, and two paratypes (ZISP 2222, 2223).

Type locality. Peru-Chile Trench, RV Akademik Kurchatov, cruise 4, st.240, 23°50’0’’S, 71°06’0’’W, 4600 m, 23.09.1968.

Etymology. After my colleague Dr. James H. McLean, Los Angeles County Museum, Los Angeles, U. S. A., who is a skilled taxonomist of marine gastropods and chitons.

Material examined. Holotype, BL— 10 mm; RV Akademik Kurchatov, cruise 4, st. 554, 22°05’0’’S, 71°26’0’’W 3980 m, paratype ( ZISP 2222), BL— 10 mm; RV Akademik Alexander Karpinskiy, st. 155, 10°03’09’’S, 86°11’04’’W, 4255 m, paratype ( ZISP 2223), BL— 17 mm, 0 9.1987, leg. O. Alexeeva.

Distribution. Peru-Chile Trench, 3980–4600 m

Diagnosis. Animal of small size. Shell low, subcarinated. Head valve wider than tail valve. Mucro central, indistinct. Tegmentum with granules of irregular shape arranged quincuncially. Each granule with one megalaesthete and two micraesthetes in front. Dorsal scales sharply pointed with one riblet. Major lateral teeth of radula has unidentate head. Nine gills per side.

Description. Holotype 10.0 x 4.9 mm. Valves subcarinated, moderately elevated (elevation ratio 0.39 in valve V), not beaked. Color of tegmentum white. Head valve semicircular, wider than tail valve. Intermediate valves rectangular, lateral areas slightly raised, anterior margin convex, posterior margin straight, not beaked. Length of tail valve shorter than half the width, mucro indistinct, antemucronal and postmucronal slopes weekly convex.

Tegmentum uniformly sculptured with quincuncially arranged granules of irregular shape, each granule with one megalaesthete and two micraesthetes in front, all three aesthete pores of approximately equal size.

Articulamentum well developed, apophyses small, widely separated.

Girdle very narrow (about 0.3 mm near valve V, 6.5 % of body width), dorsally covered with elongate, sharply pointed scales (85 x 26 µm) with one distinct riblet. Intersegmental areas with long needles (180 x 16 µm). Marginal needles 151 x 15 µm. Ventrally, the girdle is covered with elongate smooth scales (107 x 28 µm).

Radula of holotype 3.8 mm long, with 26 transverse rows of mature teeth, central teeth oval, major lateral teeth with unidentate heads.

Nine gills per side arranged from valve VII to anus.

Remarks. Leptochiton macleani n. sp. is similar to L. belknapi , L. alveolus , L. giganteus , L. sigwartae , L. halistreptus and L. mutschkeae . It differs from L. belknapi in having one rib on the dorsal scales (two in L. belknapi ), an indistinct mucro (distinct in L. belknapi ) and the absence of a small inner denticle on the cusp of the major lateral radula tooth (large outer and small inner denticle in L. belknapi ). Leptochiton mcleani differs from L. alveolus in having three pores in the aesthete group (five in L. alveolus ), one rib on the dorsal scales (two in L. alveolus ), an indistinct mucro (distinct in L. alveolus ) and a subcarinated shell (rounded in L. alveolus ). Leptochiton mcleani differs from L. sigwartae in having three pores in the aesthete group (five pores in L. sigwartae ), an indistinct mucro (distinct in L. sigwartae ), a tail valve narrower than the head valve (tail valve distinctly wider than head valve in L. sigwartae ), one rib on the dorsal scales (two in L. sigwartae ) and a low shell (high shell in L. sigwartae ). Leptochiton mcleani differs from L. mutschkeae in having three pores in the aesthete group (five pores in L. mutschkeae ), one rib on the dorsal scales (two in L. mutschkeae ) and shorter granules on the tegmentum (elongated granules in L. mutschkeae ). The new species differs from L. giganteus in having an indistinct mucro (distinct in L. giganteus ), a wider jugal sinus and a shorter antemucronal area. Leptochiton halistreptus differs from L. mcleani by having an extensive row of gills arranged from the anus to valve V, two ribs on the ventral scales and a tail valve which is wider than the head valve.

Figures

FIGURE 34. Leptochiton mcleani n. sp. Holotype, (ZISP 2221). Peru-Chile Trench, RV Akademik Kurchatov, st. 240, BL— 10.0 mm. A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Valve VI, ventral view; E. Valve V, detail of tegmentum surface of central area; F. Valve VIII, lateral view; G. Valve V, rostral view.

FIGURE 35. Leptochiton mcleani n. sp. Holotype, (ZISP 2221). Peru-Chile Trench, RV Akademik Kurchatov, st. 240, BL— 10.0 mm. A, C. Dorsal and ventral scales; B, D. Central portion of radula.

FIGURE 36. Leptochiton mcleani n. sp. Holotype, (ZISP 2221). Peru-Chile Trench, RV Akademik Kurchatov, st. 240, BL— 10.0 mm. A. Sutural needle; B. Dorsal scale; C. Marginal needle; D. Ventral scale; E. Central and first lateral teeth; F. Heads of major lateral tooth; G. Aesthete group in central area. Scale bar 100 µm (A – F).