Propeamussium meridionale (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 : 126

Propeamussium meridionale (E. A. Smith, 1885)

Figs 4D–E,G–H

Amussium meridionale Smith, 1885: 316 , pl. 24, figs 1–1a.

Amusium (Propeamusium) [sic] malpelonium Dall, 1908: 405 , pl. 6, fig. 9.

Propeamussium meridionale (Smith) .–Grau, 1959: 12, pl. 1; Knudsen, 1970: 94, pl. 12, figs 5–9, text-fig. 58; Dell, 1990: 37; Dijkstra, 1995b: 19, figs 15–18, 143–146 [lectotype]; Dijkstra, 2001: 78; Dijkstra & Marshall, 2008: 3, figs 1, 3A–G; Dijkstra & Maestrati, 2008: 83; Spencer et al., 2009: 198; Dijkstra & Janssen, 2013: 187, figs 13–14; Dijkstra & Maestrati, 2013b: 470.

Propeamussium malpelonium (Dall) .–Grau, 1959: 14, pl. 2, fig. 1.

Varlamussium [sic] meridionale (Smith) .– Powell, 1960: 175.

Propeamussium (Propeamussium) malpelonium (Dall) .– Clarke, 1962: 59.

Verlamussium [sic] meridionale (Smith) .–Clarke, 1962: 60.

Amussium meridionale Smith.– Knudsen, 1967: 277, pl. 1, fig. 16, text fig. 17.

Amusium (Propeamusium) [sic] malpelonium Dall. –Boss et al., 1968: 197.

Propeamussium (Propeamussium) meridionale (Smith) .– Dijkstra, 1990a: 2, 9, pl. 1, figs 1–2.

Type data. Amussium meridionale : lectotype (pr) NHMUK 1887.2 .9.3337, designated by Dijkstra (1995b: 19), 2 paralectotypes (lv) NHMUK 1887.2.9.3335/1–2. Type locality: Southern Indian Ocean, 50°01'S 123°E, alive, 3292 m (Challenger stn 158) .

Amusium (Propeamusium) [sic] malpelonium : 16 syntypes (7 pr + 9 v) USNM122871, type locality: Panama, SW of Isla Jicarón , 06°17'N 82°05'W, alive, 3058 m (Albatross stn 3360) ; 17 syntypes (8 pr + 9 v) USNM122872, type locality: Panama, S of Punta Burica , 06°10'N 83°06'W, alive, 2690 m (Albatross stn 3361); 20+ syntypes (pr) USNM122873, type locality: Colombia, SW of Isla De Malpelo, 02°35'N 83°53'W, alive, 3354 m (Albatross stn 3374) ; 6 syntypes (pr) USNM122874, type locality: Colombia, NE of Isla de Malpelo, 04°56'N 80°52'30"W, alive, 3241 m (Albatross stn 3381) .

For comments on the type material of Propeamussium meridionale see Dijkstra (1995b: 19), and for P. malpelonium see Kabat (1996: 13).

Extralimital material examined. There are no records from the continental shelf of Australia. Smith (1885:316) recorded Propeamussium meridionale from Challenger Expedition stn 158 (50°01'S 123°04' E) in the northern region of the Southern Ocean , south of Western Australia in 1800 fathoms [3292 m], outside the continental shelf of the mainland. — NEW CALEDONIA: 24°28'S 168°08'E, 2160 m, alive (2 pr, ZMA Moll.145142). — TASMAN SEA: Lord Howe Rise, 27°13.34'S 160°43.41' E, 1989 m, grey ooze, alive (1 pr, C.165413); 36°55.7'S 159°31.5'E, 4954–4981 m, alive (2 pr, ZMA Moll. 145035). — NEW ZEALAND: Three Kings Rise, Tasman Basin, and Bounty Trough (to 46°38.80' S 178°30.03'E, 2780 m), living at 760–4981 m (Dijkstra & Marshall, 2008:5, fig. 1) .

Description. Shell up to c. 15 mm high, fragile, somewhat inequivalve, almost circular, left valve slightly more convex than right valve, auricles equal, umbonal angle about 120°. Prodissoconch c. 200 µm high ( Knudsen, 1967). Pellucid white.

Left valve sculptured with delicate radial lirae, commencing at 3 mm shell length, extending almost to ventral margin. Prominent commarginal lamellae extend to ventral margin, intersected by radial lirae to produce a somewhat reticulate sculpture. Auricles equal, with antimarginal striae. Some delicate lamellae near anterior and posterior margins.

Right valve covered with evenly spaced commarginal lirae, more close-set near margins. Auricles differently sculptured: anterior with more prominent antimarginal lirae than posterior, commarginal lamellae present near dorsal margin. Internal riblets variable in number, 12 in most specimens, without distinct terminal nodules. Dorsal margin straight with fine scales along margin. Resilifer triangular. No byssal notch.

Habitat. Living in the bathyal and abyssal zones, free on soft muddy bottoms.

Distribution. Southern Western Australia, 3292 m; East of Marion Island, Indian Ocean, 2516 m ( Smith, 1885); northern Arabian Sea, 1893 m; Zanzibar area, East Africa, 2926 m; Maldive Islands , 1829–2051 m; Gulf of Aden, 2000 m ( Knudsen, 1967); Indian Ocean, 3390–4820 m; Tasman Sea, 4670 m; Kermadec area, 2470–2640 m ( Knudsen, 1970); Chesterfield Islands , Coral Sea, 1100 m; New Caledonia, 690–920 m, 2160–2470 m, and Loyalty Islands , 760–2350 m (Dijkstra, 1995b, 2001);

Wallis and Futuna Islands , 700–900 m; Vanuatu , 641–786 m (Dijkstra, 2001); Norfolk Ridge, 923 m (dead); Fiji , 650–707 m; Tonga , 200–983 m (dead) (Dijkstra & Maestrati, 2008). The maximum depth range of live-taken specimens is 641–4954 m. Present specimens from the Tasman Sea living at 1989 m and 4954 m.

Remarks. Knudsen (1970: 96) considered that the present species is morphologically identical to Propeamussium malpelonium (Dall, 1908) , recorded from abyssal depths in the tropical eastern Pacific. Dijkstra (1990a: 2) suggested that Propeamussium zoniferum (Dautzenberg & Bavay, 1912) , known from bathyal depths off Indonesia, is very similar to P. meridionale and differs only a little in the sculpture of the left valve ( P. zoniferum is almost smooth and hyaline, P. meridionale opaque with delicate radial and commarginal sculpture).

Hicks & Marshall (1985: 228) stated that most gut samples of this carnivorous species contain harpacticoid copepods. Knudsen (1970: 96) also found crustaceans in the stomach. For information on reproduction and biology of the present species see also Knudsen (1970: 96).