Leptochiton, Gray, 1847

Sirenko, B. I., 2022, A new tiny Leptochiton (Mollusca: Polyplacophora) from the Persian Gulf, Ruthenica, Russian Malacological Journal 32 (3), pp. 115-120 : 116-119

Leptochiton persianus sp. nov.

( Figs 1–4 )

Zoobank registrtation: urn:lsid:zoobank.org:act:CBC75A2E-6A88-463B-93A5-B1E95C960829

Type material. Holotype ( ZIN No 2438), and 10 paratypes ( ZIN No 2439).

Type locality. Indian Ocean, the northern part of the Persian Gulf, the Iranian coast.

Etymology. After the Persian Gulf.

Distribution. Only known from the type locality.

Diagnosis. Animal minute, elongate-oval. Valves are rounded, not beaked, moderately elevated, while tail valve is very high with subcentral mucro, length of antemucronal area larger than length of postmucronal area, lateral area do not rise. Tegmentum sculptured with oval or rounded, flattened granules arranged in longitudinal rows in central areas of intermediate valves and in antemucronal area of tail valve. In other areas granules arranged in quincuncial pattern. Each granule with 1 megalaesthete and 2–4 micraesthetes. Girdle densely covered with dorsal scales with 13-14 ribs; sutural and marginal needles narrow, ribbed and bluntly pointed. Central and first lateral teeth of radula long, major lateral teeth of radula with tridentate cusp.

Description. Holotype 2.0 mm, elongate oval. Valves moderately elevated, dorsal elevation 0.40, dorsum evenly rounded, not beaked. Head valve semicircular. Intermediate valve short, rectangular, side margin rounded, lateral areas hardly rised; anterior and posterior margin nearly straight. Tail valve very high, mucro subcentral, length of antemucronal area larger than length of postmucronal area, antemucronal area strongly convex, postmucronal slope a little concave directly behind the mucro.

Tegmentum granulose. On head valve, lateral areas of intermediate valves, and postmucronal area of tail valve granules oval, randomly arranged. Central areas of intermediate valves and antemucronal area of tail valve with longitudinal chains of roundish, flat, weakly raised granules, in central area 20 chains of granules. Each granule with 1 megalaesthete and 2–4 micraesthetes disposed in front of megalaesthete.

Articulamentum weekly developed, apophyses small, triangular in intermediate valves and trapezoid in tail valve, widely separated by more or less flat sinus. Ratio of width of jugal sinus to width of apophyses 2.05.

Girdle of holotype very narrow (about 0.1 mm near valve V), dorsally densely covered with small bluntly pointed, ribbed (with ca. 13–14 ribs) on dorsal side scales (38 x 25 μm). Sutural needles long, strongly ribbed (60–100 x 6–7 μm). Margin armed spicules of two kinds: long, ribbed rare needles similar with sutural ones and numerous finely ribbed on dorsal side (6–7 ribs) scales (50 x 10 μm) with a sharply pointed distal end. Ventral side of the girdle clothed with two kind of scales: broad scales (36 x 18 µm) with 6–7 short ribs in the distal half of the ventral part arranged in a row at the margin, and narrow oval scales (30 x 11 μm) obtusely pointed at distal end.

Radula of holotype 0.6 mm long with 51 trans- verse rows of mature teeth. Central tooth rectangular, about 3 times as long as wide, with a narrow blade; first lateral tooth narrow, about the same length as the central one, with small blade; major lateral teeth with thin tridentate cusp, median denticle round on top and much longer than others.

Holotype with 6 gills of nearly equal length on each side extending from valve VI to valve VIII

Remarks. New species superficially strongly resembles L. muelleri , but differs primarily by having long first lateral tooth which is as long as the central tooth (vs. first lateral tooth noticeably shorter that the central tooth in L. muelleri ), subcentral mucro: length of the antemucronal area exceeds the length of the postmucronal area (vs. mucro anterior, antemucronal area is shorter than postmucronal area in L. muelleri ), hardly raised lateral areas (vs. lateral area weakly raised in L. muelleri ), and rounded tip of the median denticle of the head of the major lateral tooth of the radula (vs. sharply pointed at the top in L. muelleri ).

L. persianus sp. nov. differs from L. nierstraszi in having longitudinal arrangement of granules in entire central area of intermediate valves (vs. quin- cuncially arrangement of granules in jugal area in L. nierstraszi ), tridentate cusp of major lateral teeth of radula (vs. unidentate cusp in L. nierstraszi ).

New species differs from L. hiriensis in having widely separated granules in tegmentum (vs. closepacked granules in L. hiriensis ), and no traceable commarginal sculpture (vs. strong commarginal ridges in valves of L. hiriensis ).

L. persianus sp. nov. differs from L. pumilus in having central mucro (vs. anterior mucro in L. pumilus ), in randomly arranged granules on head valve, lateral areas of intermediate valves, and postmucronal area of tail valve (vs. in radial rows in L. pumilus ).

New species differs from L. myeikensis in having 5 pores of aesthetes in a granule (vs. 9–11 pores in L. myeikensis ), randomly arranged granules on head valve, lateral areas of intermediate valves, and postmucronal area of tail valve (vs. in radial rows in L. myeikensis ).

New species superficially resembles L. scabridus (Jeffreys, 1879) and differs from the latter, in having the tegmentum of the head valve, lateral areas of intermediate valves and postmucronal area of tail valve sculptured with granules arranged in a random manner (vs. the tegmentum of the mentioned areas is sculptured with granules arranged in radial lines in L. scabridus ), higher tail valve (vs. low tail valve in L. scabridus ), narrower dorsal scales (38 x 25 µm), without thickening of the base (vs. dorsal scales are wider (92 x 84 µm) with a noticeably thickened base in L. scabridus ), and the lateral areas which are dominated by growth lines (vs. the lateral areas are covered with radial rows of granules in L. scabridus ).

Figures

FIG. 1. Leptochiton persianus sp. nov., paratype (ZIN No.2439), Persian Gulf, Indian Ocean, BL–2.0 mm.A. Whole specimen, dorsal view.B. Valve V,VI, VII,VIII, lateral view, dorsal scales, sutural and marginal needles and marginal scales. C. Whole specimen, lateral view. D. Valve IV, V, dorsal view and sutural needles.