Leptochiton sigwartae, 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 : 193-195

Leptochiton sigwartae n. sp.

( Figs 37–39 )

Types. Holotype (ZISP 2205), 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 one paratype (ZISP 2206).

Type locality. Peru, RV Akademik Alexander Karpinskiy, st. 105, 06°41’S, 80°48’W, 822 m.

Etymology. Named after Dr. Julia Sigwart, Queen’s University Belfast, Marine Laboratory, Northern Ireland, who is a good specialist on primitive chitons.

Material examined. Holotype, BL— 17 mm and paratype BL— 17 mm, from type locality, September 1987, leg. O. Alexeeva.

Distribution. Only known from type locality.

Diagnosis. Animal medium in size, elongate oval. Valves very highly elevated, carinated. Tail valve distinctly wider than head valve, with central mucro. Tegmentum with raised granules, closely adjacent and arranged quincuncially. Each granule with one megalaesthete and four micraesthetes in front. Dorsal scales with two distinct riblets. Central teeth of radula wide and with scissura low on base. Third uncinal teeth narrow distally. Major lateral teeth with unidentate head. Thirteen gills per side from valve VI to anus.

Description. Holotype 17.0 x 6.0 mm. Valves thick, carinated, very highly elevated (elevation ratio 0.62 in valve V), slightly beaked. Color of tegmentum white. Head valve semicircular, narrower than tail valve (ratio of width of tail valve to width of head valve 1.1). Intermediate valve rectangular, lateral area not raised, anterior margin concave, lateral margins rounded, posterior margin slightly beaked. Tail valve triangular, mucro central, postmucronal slope slightly concave.

Tegmentum uniformly sculptured with raised, hardly separated, quincuncially arranged granules, except for pleural areas where granules arranged in oblique rows. Each granule with one megalaesthete and four micraesthetes in front, pores of megalaesthete (8 µm) a little larger than micraesthetes (5–6 µm).

Articulamentum well developed, apophyses small, widely separated.

Girdle narrow (about 0.5 mm near valve V 9.4% of total width, dorsally covered with sharply pointed scales (68– 70 x 25 µm) with two distinct riblets and numerous scattered long needles (150 x 18 µm). Marginal needles shorter than dorsal ones (110–113 x 17 µm). Ventrally girdle covered with elongate, smooth, bluntly pointed scales (80 x 18 µm).

Radula of holotype 4.7 mm long with 25 transverse rows of mature teeth. Central tooth wide and with basal notch. Major lateral teeth with unidentate cusps. Distal part of third uncinal teeth narrowed.

Thirteen gills per side arranged from valve VI to anus.

Remarks. The new species superficially resembles Leptochiton belknapi , L. giganteus , and L. japonicus but differs from them in having much higher valves and a triangular tail valve which is wider than the head valve. Moreover it differs from L. belknapi in having more micraesthetes per megalaesthete and a narrowed distal part of third uncinal teeth of the radula and from L. japonicus by fewer riblets on the dorsal scales and in the arrangement of granules which are closer to each other. Leptochiton sigwartae differs from L. giganteus in having a wider jugal sinus, a shorter antemucronal area, a higher shell and two ribs on the dorsal scales (no ribs in L. giganteus ). Leptochiton halistreptus differs from the new species in having an extensive row of gills arranged from the anus to valve V, two ribs on the ventral scales and a less elevated shell. For differences of L. sigwartae from L. macleani and L. mutschkeae see in the remarks to those species.

Figures

FIGURE 37. Leptochiton sigwartae n. sp. Holotype, (ZISP 2205). Peru-Chile Trench, RV Akademik Karpinskiy, st. 105, BL— 17.0 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 38. Leptochiton sigwartae n. sp. Holotype, (ZISP 2205). Peru-Chile Trench, RV Akademik Karpinskiy, st. 105, BL— 17.0 mm. A. Valve VIII, detail of tegmentum in antemucronal area; B, C. Dorsal, marginal and ventral scales and needles; D. Central portion of radula.

FIGURE 39. Leptochiton sigwartae n. sp. Holotype, (ZISP 2205). Peru-Chile Trench, RV Akademik Karpinskiy, st. 105, BL— 17.0 mm. A. Sutural needle; B. Dorsal scale; C. Marginal needle; D. Ventral scale; E. Aesthete group in central area; F. Central and first lateral teeth; G, H. Heads of major lateral tooth. Scale bar 100 µm (A – D, F – H).