Leptochiton sigwartae Sirenko, 2015

Sirenko, Boris & Sellanes, Javier, 2016, Update of the genus Leptochiton (Mollusca: Polyplacophora) in Chilean deep waters: three new reports and description of two new species, Zootaxa 4173 (3), pp. 259-279 : 264

Leptochiton sigwartae Sirenko, 2015 .

( Figs 1 C, D, 5–8)

Type material. Holotype (ZISP 2205).

Type locality. Peru, 06°41’S, 80°48’W, 822 m depth.

Material examined. Off Chile, near Chiloe, 42.3504°S, 74.4809°W, 502 m depth, RV Sonne, st. SO-156, 7176-5, 1 spm ( ZISP 2275 ), BL—33.0, 2 spms (SCBUCN 4137), BL—33.0– 33.5 mm, 0 2.05.2001.

Distribution. Off Peru and Chile, 502–822 m depth. This find off Southern Chile extends the distribution of this species considerably.

Amended description. Specimen 33.5 mm. Valves thick, carinated, very highly elevated (elevation ratio 0.53 in valve V), slightly beaked. Valves slope slightly concave. Color of tegmentum white with black deposits on old parts of valves.

Head valve semicircular, slightly wider than tail valve (ratio of width of tail valve to width of head valve 0.95). Intermediate valve beaked, anterior margin decidedly curved inward, lateral areas slightly raised, lateral margin rounded. Tail valve with somewhat swollen, subcentral mucro, postmucronal slope concave.

Tegmentum uniformly sculptured with raised, quincuncially arranged granules. Each granule with one megalaesthete and four micraesthetes in front, megalaesthetes slightly larger than micraesthetes.

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

Girdle narrow (about 2.3 mm near valve V), dorsally covered with sharply pointed, smooth, slightly curved scales (86 x 22 µm), and scattered long needles (260 x 26 µm). Intersegmental needles similar but longer (292 x 24 µm). Marginal needles shorter than dorsal and sutural needles (210 x 22 µm). Ventrally girdle covered with elongate smooth, sharply pointed scales (93 x 20 µm).

Radula of specimen studied 8.5 mm long with 31 transverse rows of mature teeth. Central tooth wide with rounded base. Major lateral teeth with sharp unidentate cusps.

Fifteen gills per side arranged from valve VII to anus.

Remarks. The present material shows some differences to the type material and so we have decided to include an amended description. The new specimens differ from type specimens of L. sigwartae in having the tail valve narrower than the head valve (tail valve wider than the head valve in holotype), smooth dorsal scales or with up to three indistinct ribs (two ribs in holotype). In our opinion, the differences described above fall within the limits of intraspecific variability.

Figures

FIGURE 1. Complete specimens of Leptochiton belknapi Dall, 1878. BL— 23 mm, RV Melville, st. INSPIRE, AGT- 3 _ 533, 724 m, SCBUCN 4136 (A, B), Leptochiton sigwartae Sirenko, 2015. BL— 33 mm, RV Sonne, st. SO- 156. 7176 - 5, 502 m, ZISP 2275 (C, D), Leptochiton laurae Schwabe & Sellanes, 2010. BL— 11,5 mm, RV Melville, st. INSPIRE, AGT- 2, 583. 497 – 574 m, ZISP 2276 (E, F), Leptochiton ibanezi sp. nov., holotype, BL— 21 mm, MNHNCL 400187 (G, H). A, C, E, G. Dorsal view; B, D, F, H. Lateral view. Scale bars 2 mm.