Leptochiton subrugatus Sirenko & Sigwart, 2021

Leptochiton subrugatus Sirenko & Sigwart, 2021 View in CoL

( Figs. 1 - 4 View Fig View Fig View Fig View Fig ) 아"군부 ( *명승계)

Leptochiton subrugatus Sirenko and Sigwart, 2021: 3 - 8 View in CoL , figs. 1 - 4.

Lepidopleurus assimilis View in CoL : Taki, 1938: 328 - 331, pl. 14, fig. 2, pl. 16, figs. 5, 9 - 13, 15, pl. 17, figs. 9 - 11; Jakovleva, 1952: 55, fig. 16, pl. 1, fig. 4 (non Lepidopleurus assimilis Thiele, 1909 View in CoL , partim).

Leptochiton assimilis View in CoL : Saito, 1995: 100; 2000: 4, 5, fig. 1; 2017: 728, pl. 2, fig. 3 (non Lepidopleurus assimilis Thiele, 1909 View in CoL , partim).

Leptochiton ( Leptochiton) rugatus View in CoL : Kaas and Van Belle, 1985: 85 - 87, fig. 37, map 15; Dell̓Angelo et al., 1990: 32 - 34, pl. 1, figs. 1 - 6, pl. 2, figs. 1 - 7, textfig. 2 (non Lepidopleurus rugatus Carpenter View in CoL in Pilsbry, 1892, partim).

Leptochiton rugatus View in CoL : Ferreira, 1979: 146 - 149, figs. 1, 2, 7, 33, 34; Slieker, 2000: 82, 83, pl. 29, fig. 3; Qi, 2004: 3, pl. 1A; Sigwart et al., 2011; Sirenko, 2013: 148; Sigwart, 2017 (non Lepidopleurus rugatus Carpenter View in CoL in Pilsbry, 1892, partim).

Leptochiton sp. 2 : Sigwart and Chen, 2018.

Material examined. Korea: total 14 individuals: 4 individuals: Munamjin-ri, Jugwang-myeon, Goseong-gun, Gangwon-do ( 38°18 ʹ 04.4 ʺ N, 128°34 ʹ 10.8 ʺ E), collected by SCUBA diving at depth of 29 m, 05 May 2021; 7 individuals: Munamjin-ri, Jugwang-myeon, Goseong-gun, Gangwon-do ( 38°18 ʹ 02.4 ʺ N, 128°34 ʹ 12.2 ʺ E), collected by SCUBA diving at depth of 28 m, 06 May 2021; 3 individuals: Munamjin-ri, Jugwang-myeon, Goseong-gun, Gangwon-do ( 38°18 ʹ 04.2 ʺ N, 128°34 ʹ 15.0 ʺ E), collected by SCUBA diving at depth of 32 m, 06 May 2021. All specimens are deposited in the Animal Phylogenomics Laboratory at Ewha Womans University in Seoul GoogleMaps , Korea.

Description. Body elongate-oval, small in size ( Fig. 1A View Fig ; in examined specimen, Body Length 4.85 mm, Body Width 2.28 mm). Valves thin, creamy-white in color, sometimes stained with yellow-brown to black by environmental deposits. Girdle very narrow, white to dirty yellow in color. Gills arrangement adanal and merobranchial on both sides, from 6th valve to the anus ( Fig. 1B View Fig ).

Head valve semicircular with dense granules arranged in indistinct radial lines and concentric growth lines; granules very small, uniform in size, rounded oval in shape; posterior margin widely V-shaped and nearly straight ( Fig. 2A View Fig ). Intermediate valves similar from 2nd valve to 7th valve in width, broadly rectangular in shape, not beaked; anterior and posterior margins nearly straight, lateral margins rounded ( Fig. 2B, C View Fig ). Intermediate valves dorso-ventrally rounded, not carinated, and moderately elevated in frontal view ( Fig. 2E View Fig ; elevation ratio of 0.64 - 0.79 in the 5th valve); tegmentum of central area (ca) sculptured with small rounded granules densely arranged in longitudinal rows ( Fig. 2B, C, H, I View Fig ); lateral areas (la) not raised, with granules arranged in fine radial rows and several growth lines ( Fig. 2B, C, I View Fig ); each granule with 3 - 5 aesthete pores, comprising one megalaesthete (me) and two to four micraesthetes (mi). Tail valve semicircular and wider than head valve; mucro (m) antemedian, protruding, slightly pointed; sculpture of antemucronal area (ama) same as central area of intermediate valves; postmucronal area (pma) similar to head valve and lateral area of intermediate valves ( Fig. 2D View Fig ); anterior margin slightly convex; antemucronal and postmucronal slope (ams, pms) almost straight ( Fig. 2G View Fig ). Articulamentum white, no insertion plate; apophyses (ap; sutural laminae) widely separated, short, triangular in shape, and hyaline; jugal sinus (js) wide and shallow; central calluses (cc) relatively thick and prominent ( Fig. 2F View Fig ); numerous pores in radial rows, except for two central calluses connected from apophyses to ventral tegmental callus (vtc); eaves (e) very thin.

Perinotum densely covered with flat, curved, ovate scales (perinotum scale; ps: length 51.1 μm, width 31.3 μm) with blunted-tip and 13 - 18 longitudinal ribs, longer near sutures ( Fig. 3A - C View Fig ); outer margin densely covered with small marginal spicules (msp: length 77.4 μm, width 15.7 μm) with obtusely pointed tip and strong radial ribs ( Fig. 3A - C View Fig ); sporadic marginal spines (mp: length 139 μm, width 12.5 μm) long, slender, pointed, almost smooth, with faint longitudinal lines ( Fig. 3A - C View Fig ); hyponotum covered with elongate, flat, overlapping scales (hyponotum scale; hs: length 77.8 μm, width 33.1 μm) with obtusely pointed tip and 6 - 9 longitudinal ribs at the tip ( Fig. 3A, D View Fig ).

Radula teeth ( Fig. 4 View Fig ) symmetrical, measuring 2.57 mm length, with 96 transverse rows of mature teeth. Central tooth (c) narrow with a small cusp bent forward; two centro-lateral teeth (cl) long with blades bent inwardly; head (h) of major lateral teeth (mlt) unicuspid, each cusp narrow, bluntly pointed; major uncinal teeth (mu)