Leptochiton laurae Schwabe & Sellanes, 2010

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 : 264-271

Leptochiton laurae Schwabe & Sellanes, 2010

( Figs 1 E, F, 9–11)

Type material. Holotype (ZSM Mol 20070760).

Type locality. Chile, off Concepcion , 36°22.19’S, 73°43.36’W, 846 m.

Material examined. Off Chile, RV AGOR Vidal Gormáz, st. VGO7-02, AGT-04, 34.4284– 34.4267°S, 72.2309 –72.2247°W, 922–949 m, 1 spm, BL— 10.5 mm, 30.09.2007; RV Melville st. INSPIRE, AGT-2_583, 46.54115°S, 75.35997°W , 497–574 m depth, 1 spm (ZISP 2276) BL—9.5, 6 spms (SCBUCN 4138), BL—9.5–15.0 mm, 0 6.03. 2010; st. INSPIRE, AGT-1_594, 46.55216°S, 75.34852°W, 460 m depth, 1 spm (SCBUCN 4139), BL— 8 mm, 06.03.2010; INSPIRE, AGT-3_ 533 m, 36.22523°S, 73.43115°W, 724 m depth, 8 spms (SCBUCN 4140), BL—11.0–15.0 mm, 0 9.03.2010.

Distribution. Off Chile, from 34.4284°S to the Magellan Strait and Beagle Channel, South Orkney, South Shetland, Kerguelen and Crozet Islands, 88–1200 m. The present report extends the previously known distribution of this species.

Amended description. Specimen 10.0 x 4.9 mm. Valves thick, rounded, moderately elevated (elevation ratio 0.44 in valve V) not beaked. Color of tegmentum white. Head valve semicircular. Intermediate valves rectangular, not beaked, lateral area not raised, anterior margin concave, posterior margin slightly convex, lateral margins rounded. Tail valve same size as head valve, triangular; mucro anterior, antemucronal slope convex, postmucronal slope concave. Head valve, lateral areas and postmucronal area with distinct growth line.

Tegmentum sculptured with distinct oval granules, arranged in longitudinal rows on central area of intermediate valves and antemucronal area of tail valve, in radial rows on head valve and in indistinct radial rows on lateral areas of intermediate valves, and in a random manner on postmucronal area of tail valve. Each granule with one megalaesthete and two micraesthetes in front; megalaesthetes larger than micraesthetes.

Articulamentum well developed, anophyses small, widely separated, narrower than jugal sinus (ratio of width of sinus to width of apophyses 1.6).

Girdle narrow (about 0.5 mm near valve V), dorsally covered with sharply pointed scales (63– 64 x 20 µm) with three distinct riblets and scattered long needles (145–195 x 15–20 µm) Sutural needles longer (245 x 20 µm). Marginal needles shorter than dorsal (112 x 17 µm). Ventrally the girdle covered with elongate, smooth, bluntly pointed scales (71– 82 x 16–17 µm).

Radula of 10 mm long specimen with 35 transverse rows of mature teeth. Central tooth elongate, major lateral teeth with bidentate cusp, inner denticle shorter than outer one.

Ten gills per side arranged from valve VII to anus.

Remarks. The new material shows some differences to the types and to some specimens studied by Sirenko (2015). Therefore, we provide an amended description including features shown by the new specimens. The specimens studied differ from the holotype and specimens reported by Sirenko (2015) by having a narrower body and three ribs on dorsal scales [vs. 1–2 ribs or smooth scales in the specimen studied by Sirenko (2015) and 6–8 very faint longitudinal ribs in the holotype ( Schwabe & Sellanes, 2010)]. In our opinion there is a variability of the number of ribs and dorsal scales in this species. The specimens inhabiting the southern portion of the area (South Shetland Islands) have smooth scales, those from Magellan region have 1 or rarely 2 ribs and the specimens from 46.5411°S have 3 ribs.

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.