Propeamussium siratama ( Oyama, 1951 )

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 127-128

Propeamussium siratama ( Oyama, 1951)

Figs 1F–H,J,N, 2

Ctenamusium (Micramussium) siratama Oyama, 1951: 80 , pl. 13 figs 5–7.

Propeamussium siratama (Oyama) .–Dijkstra & Kastoro, 1997: 253, figs 20–23; Hayami, 2000: 913, pl. 454 fig. 6; Dijkstra, 2001: 81, figs 21–24; 2013: 15, pl. 2, figs 1a–d, pl. 4, fig. 5; Dijkstra & Maestrati, 2008: 85; 2009: 39, pl. 1 figs 1–4; 2012: 392.

Type data. Holotype (H 7.4 mm, pr). The type material is possibly in the Toba Aquarium at Toba , Japan, but Oyama (pers. comm.) could not trace it there. Type locality: Japan, Sagami Sea, off Manazuruzaki, 159–128 fathoms [= 291– 234 m], alive.

Additional material examined. — AUSTRALIA: QUEENSLAND: E of GBR, 18°11.01'S 147°25.5'E, alive, 472–490 m (2 pr + 1 v [lv:smooth], C.165218) . WESTERN AUSTRALIA: W of Rottnest Island , 31°02'S 114°48'E,dead, 275–285 m (4 v, WAM 443.91 ) ; NW of Cape Leveque , 14°49.0'– 14°50.8' S 121°36.1' – 121°35.6'E, dead, 300–302 m (3 v, WAM 465.91 ) . — JAPAN: Mie Prefecture, Kii Peninsula, off Owase City , alive, 500 m, dredged (3 pr, ZMA Moll. 145634) . TAIWAN: NE–coast, off Tashi , 24°48.8'N 122°06.0' E, alive, 367–424 m, dredged (many prs, MNHN) . — PHILIPPINES: Luzon, Balayan Bay , 13°49'N 120°50' E, alive, 299–320 m, dredged (1 pr, ZMA Moll. 145105) . — INDONESIA: Kei Islands , 05°23'S 132°27'E, alive, 413–436 m, trawled (many prs, MNHN) . — PAPUA NEW GUINEA: SE Manus Island , 02°14'S 147°16'E, alive, 611–618 m, trawled (3 pr, MNHN) . — SOLOMON ISLANDS : Choiseul Island , 06°34.7'S 156°10.5' E, alive, 609–625 m, trawled (3 pr, MNHN) .— NEW CALEDONIA:E New Caledonia , 20°34'S 164°57'E,alive, 497–520 m, dredged (2 pr, MNHN) .— FIJI: SE Viti Levu , 17°30.9'S 178°53.3'E,alive, 879–897 m, trawled (3 pr, MNHN) .

Description. Shell fragile, up to c. 19 mm high, most specimens up to c. 10–12 mm in height, circular, nearly equivalve, equilateral, slightly inflated, auricles equal in shape and size, umbonal angle 110–115°. Prodissoconch c. 200 µm in height. Colour whitish or pale-brown transparent.

Left valve weakly sculptured (or almost lacking) with fine, irregularly spaced radial lirae from early growth stage until beyond central part of disc, with microscopic regularly spaced commarginal lamellae, smooth central part and periphery. Auricles frequently smooth, sometimes with fine commarginal lirae.

Right valve sculptured with delicate, regularly spaced commarginal lirae, more prominent near ventral margin. Inner surface with 7–9 ribs, with a riblet on each side near the auricles. Hine line straight. No byssal fasciole, or byssal notch. Ctenolium lacking.

Distribution. Japan: 100–300 m (Hayami, 2000: 913), Taiwan: 310–440 m (Dijkstra & Maestrati, 2009: 39); Philippines: 400–602 m (Dijkstra, 2013: 15); Indonesia: 283–285 m (Dijkstra & Kastoro, 1997: 253), Solomons and Fiji: 273–1004 m (Dijkstra & Maestrati, 2008: 85); New Caledonia: 316–533 m (Dijkstra, 2001: 82); Vanuatu: 509–659 m (Dijkstra & Maestrati, 2012: 392).

Present material from Australia alive in 472–490 m. The bathymetric range of live-taken specimens is 100–1004 m .

Remarks. The present specimens from Australia fit the original description (type material untraceable) and studied material from Japan (ZMA, NSMT), but differ in having fewer internal riblets (7 + 2 small auricular riblets, typically 8 + 2 small auricular riblets). Other morphological characters are identical. Oyama (1951) did not state the etymology of the species name, but did not decline it, whereas all other species name in his paper are declined to agree with the generic name. We follow Oyama (1951), assuming it is an indeclinable noun.

Propeamussium siratama is a new record for Australia.