Propeamussium caducum (E. A. Smith, 1885 )

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 : 124-125

Propeamussium caducum (E. A. Smith, 1885)

Figs 1B–C,I, 2

Amussium caducum Smith, 1885: 309 , pl. 23, figs 1–1c; Smith, 1894: 173; Smith, 1895: 18; Smith, 1904: 13; Smith, 1906: 255; Melvill & Standen, 1907: 807; Thiele & Jaeckel, 1931: 7; Winckworth, 1940: 26.

Amussium electrum Pelseneer, 1911 : pl. 12, figs 4A–B, 5 [syn. nov.].

Amussium weberi Dautzenberg & Bavay, 1912: 32 , pl. 28, figs 9–13.

Propeamussium nakazawai Kuroda, 1932: 87 , figs 101–102 (nomen nudum).

Parvamussium (Flavamussium) caducum (Smith) .– Oyama, 1951: 81, pl. 13, figs 11–12; Kira, 1967: 138, pl. 49, fig. 15.

Propeamussium caducum (Smith) .–Hayami, 1988a: 476; Okutani et al., 1989: 58, figs; Dijkstra, 1991: 6, figs 1–2; Dijkstra, 1995b: 15, figs 9–10, 129–132; Dijkstra & Kastoro, 1997: 247, figs 5–8; Hayami, 2000: 913, pl. 454, fig. 1; Dijkstra, 2001: 75; Wang, 2002: 152, pl. 2, fig. 2; Dijkstra & Maestrati, 2008: 82; Xu & Zhang, 2008: 77, fig. 208; Huber, 2010: 223; Dijkstra & Janssen, 2013: 187, figs 10–12; Dijkstra & Maestrati, 2015: 589, figs 1E–F.

Propeamussium (Propeamussium) caducum (Smith) .– Wang, 1984a: 599, pl. 1, figs 3–4, text fig. 2; Dijkstra, 1990a: 9–10.

Comments on synonyms. Synonymy established by Oyama (1951), and subsequently followed by Knudsen (1967) and Habe (1977).

Type data. Amussium caducum Smith: lectotype (pr) designated by Dijkstra (1995b: 17) NHMUK 1887.2.9.3310,

Figure 2. Distribution of Propeamussium alcocki (Smith) (circles), P. caducum (Smith) (stars) and P. siratama (Oyama) (triangles).

4 paralectotypes (pr) NHMUK 1887.2.9.3311/1-4. Type locality: Philippine Islands , W of Luzon , 12°21'N 122°15'E, alive, 1280 m (Challenger stn 207) .

Amussium electrum Pelseneer, 1911 : holotype (only soft parts figured) KBIN not traced (see Remarks).

Amussium weberi Dautzenberg & Bavay : lectotype (pr) designated by Dijkstra (1995b: 17), figured by Dautzenberg & Bavay (1912: figs 9–10, 12–13 [text incorrect, should be “Mer de Bali, drag. 538 m ”) ZMA Moll.3.12.013 ( Siboga stn 316); paralectotypes: 5 pr KBIN IG10.591 (stn 314), pr MCZ064492 (stn 314), 2 v RMNH.MOL.112107 (stn. 316), 2 pr + 7 v ZMA Moll.3.12.014 (stn 316), pr ZMA Moll.3.12.015 (stn 85), pr ZMA Moll.3.12.016 (stn 87), 4 v ZMA Moll.3.12.017 (stn 212), 7 v ZMA Moll.3.12.018 (stn 314). Type locality: Indonesia, Bali Sea, 7°19.4'S 116°49.5'E, alive, 538 m ( Siboga stn 316).

Propeamussium nakazawai Kuroda : holotype not seen. Type locality: Japan, Suruga Bay , alive, 549–732 m.

Comments on type data. The anterior and posterior margins of the left valve and the marginal apron of the right valve of the lectotype of Amussium caducum are broken off; consequently the measurements differ slightly from the original ones. The ventral apron (skirt) of the right valve is thin and frequently broken on all Propeamussium species.

Although Kuroda (1932: 87) proposed a new species name with type figures, measurements and type locality, it was not described nor compared with any other species. According to ICZN (1999, Article 13.1), Propeamussium nakazawai is a nomen nudum.

Additional material examined. — AUSTRALIA: NEW SOUTH WALES: off Ulladulla,35°30' – 35°32'S 150°48' – 150°47'E,dead, 549 m (4 v,C.165479). WESTERNAUSTRALIA: off Port Hedland ,160 mls NW, 18°42'S 116°21'E – 116°23'E, alive, 694–704 m (1 pr, WAM 552.91 ) .— JAPAN: Aichi Prefecture, Mikawa, Issiki ,alive, 200–250 m (3 pr, ZMA Moll. 144707); off Kii Peninsula, Wakayama,alive, 137–183 m (1 pr, ZMA Moll. 144720); off Mie Prefecture,alive, 400 m (3 pr, ZMA Moll. 141585) . — PHILIPPINE ISLANDS : off Cebu, alive, 680 m (1 pr, ZMA Moll. 144706) . — INDONESIA: N of Sumbawa, Bay of Sanggar, 08°18.7' S 118°18'E, alive, 500–550 m (2 pr, ZMA Moll. 144585); Tanimbar Islands , 08°36'S 131°33'E, alive, 676–699 m (12 pr, ZMA Moll. 139806) . — NEW CALEDONIA: S New Caledonia, 22°10'S 166°02'E, alive, 650–724 m (1 pr, ZMA Moll. 146247) .

Description. Shell fragile, glossy, translucent or opaque, up to c. 25 mm high, inequivalve, equilateral, somewhat higher than wide, left valve slightly more convex than right, with lateral gape, umbonal angle c. 90°, prodissoconch c. 215 µm in height ( Knudsen, 1967). Cream or brownish, right valve more deeply coloured than left.

Left valve smooth, with commarginal growth lines, no radial striations. Auricles small, also smooth, somewhat raised near margins.

Right valve with wide-set commarginal lirae, commencing at 3 mm shell height and extending to submarginal area, with interstitial microscopic radial scratches. Auricles with very delicate commarginal striae, prominent scales produced on marginal areas of hinge. Dorsal margin straight near umbo, then rising near anterior and posterior ends. Internal riblets 10 in number in most specimens, 9 or 11 in a few, slightly nodulose at distal ends. Riblets of right valve somewhat more prominent than in left valve. No byssal notch.

Habitat. Living in the bathyal zone, free on soft sediment (sand and mud).

Distribution. Gulf of Aden, 1295 m; Zanzibar area, 786 m, now extended further southwards to the northwestern area of Madagascar, 243–1020 m; Arabian Sea and Bay of Bengal, 691–1483 m; Japanese waters, c. 200 m and Philippine Islands , 548–1500 m ( Knudsen, 1967; Dijkstra & Maestrati, 2015); Indonesian Archipelago, 452–840 m ( Knudsen, 1967; Dijkstra, 1991; Dijkstra & Kastoro, 1997); New Caledonia, 450–960 m (Dijkstra, 1995b, 2001); Vanuatu, 602–650 m (Dijkstra, 2001); Solomon Islands , 367–696 m (Dijkstra & Maestrati, 2008). Now also known from Australia (New South Wales and Western Australia). Present material from Australia alive at 694– 704 m. Maximum depth range of live-taken specimens is c. 200–1500 m.

Remarks. Pelseneer (1911) did not describe or figure the shell of Amussium electrum ; he described and figured only the soft parts, which he had used for his comprehensive anatomical study. These valves and soft parts have not been recovered in the KBIN. The specific epithet is probably reduced from Bavay’s manuscript name Amussium electricum [in KBIN], which he later changed to Amussium weberi . However, as the anatomy was described by Pelseneer (1911), A. electrum is an available name, a further synonym of P. caducum . Propeamussium weberi is morphologically similar to P. caducum , although in typical material the coloration ( P. caducum hyaline and whitish, P. weberi hyaline and creamy) and internal riblets ( P. caducum 8, P. weberi 7) are slightly different. However, intermediate variations are also observed.

Propeamussium caducum is a new record for Australia and in all morphological characters Australian specimens are identical to the type specimens from the Philippine Islands .