Juxtamusium coudeini (Bavay, 1903)

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 : 198-199

Juxtamusium coudeini (Bavay, 1903)

Figs 40B,D,F,H,K, 42, 43B,E–F,H

Pecten (Chlamys) coudeini Bavay, 1903: 401 , pl. 8, figs 3–4; Bavay, 1904a: 206; Dautzenberg & Bavay, 1912: 17.

Juxtamusium oblectatum Iredale, 1939: 368 , pl. 5, figs 27–27a; Waller, 1972a: 250, 252, 254, pl. 8, figs 128–133, 135.

Chlamys (Juxtamusium) oblectata (Iredale) .–Hertlein, 1969: N357, fig. C.80.4a–b.

Juxtamusium coudeini (Bavay) .– Waller, 1984: 211; Dijkstra, (1983–1989) 1984: 8, figs; Dijkstra, (1983–1994) 1985: 10, figs; Dijkstra, 1990: 3, figs; Dijkstra, 1998a: 22; Dharma, 2005: 250, pl. 100, fig. 9; Raines & Poppe, 2006: 124–125, lower figs; pl. 74, figs 2, 4, 6–7; Huber, 2010: 200; Raines, 2010: 608, pl. 995, figs 12, 14–15; Dijkstra, 2013: 44, pl. 11, figs 3a–d, pl. 27, figs 2a–b.

Type data. Pecten (Chlamys) coudeini Bavay : holotype (pr) KBIN IG10591. Type locality: New Caledonia.

Juxtamusium oblectatum Iredale : holotype (pr) AM C.075282 (Fig. 40H, K). Type locality: Australia, N QLD, 0.5 miles W of North Direction Isle , 36.5 m (Great Barrier Reef Expedition stn 16).

Additional material examined. — AUSTRALIA: QUEENSLAND: GBR, E of Snake Reef , 14°29'S 145°03'E, dead, 24 m (1 v, C.119793) ; Lizard Island, Granite Bluff , 14°39'S 145°27'E, dead, 23 m (3 v, C.338775) ; Lizard Island, Watsons Bay , 14°40'S 145°27' E,alive, 12 m (1 pr,C.343927) ; 0.5 ml SE of Lizard Island , 14°41'S 145°29' E, dead, 35 m (1 v, C.157730) ; 05. ml W of North Direction Isle , 14°45'S 145°30' E, 36 m (1 pr, alive, C.075282; 3 v, dead, C.157731) ; Cairns Reef lagoon & between Cairns Reef & Hope Island , 15°42'S 145°30'E, dead, 9–18 m (7 v, C.027533) ; N of Cairns , 16°33'S 146°09'– 146°09.6'E, dead, 55 m (3 v, C.157660) ; Michaelmas Cay, 16°36'S 145°59'E, dead (4 v, C.119792); off Townsville , 6–7 mls E of Keeper Reef, 18°45'S 147°23'E, dead, 43 m (1 v, C.338776) . — PHILIPPINE ISLANDS : Bohol, Calituban Island , alive, 20–30 m (1 pr, ZMA Moll.139895) . — INDONESIA:

Description. Shell small, up to 32 mm high, most specimens c. 20 mm; rather thin, circular to ovate, flattened (left valve almost flat, right valve weakly inflated), inequivalve, almost equilateral, auricles unequal in shape and size, umbonal angle c. 85–95°; left valve brightly coloured with white, red, yellowish or brown blotches, right valve paler.

Both valves sculptured with almost obsolete, evenly spaced radial costae and minute, closely spaced commarginal striae continuing across costae throughout. Auricles with only commarginal microsculpture, as on disc. Weak internal expressions of external radial costae with sharply raised edges near ventral margin, but not carinate. Functional right and left ctenolia very weak or even lacking. Byssal notch and fasciole absent. Resilium oblong and oblique.

Dimensions. Illustrated specimens: QLD, GBR, NE of Cairns, 55 m, two unmatched valves ( AM C.157660): rv: H 14.8, L 14.5 mm; lv: H 19.3, L 18.5 mm; QLD, GBR, Keeper Reef, off Townsville, 43 m ( AM C.338776): lv: H 20.6, L 20.8 mm. Iredale (1939: 368) stated the dimensions of the holotype of Juxtamusium oblectatum as H 22.5, L 22, D 6 mm .

Habitat. Living in the intertidal to sublittoral zones amongst coral rubble or algae on flat sandy bottoms.

Distribution. Throughout the tropical Indo-West Pacific from the Philippines to northern Australia and westwards to the central Indian Ocean (not recorded from the western Indian Ocean), and eastwards to the Fiji Islands (Raines & Poppe, 2006: 126); Philippines, 20–80 m ( Raines, 2010: 608); Philippines, 12–20 m; Marshall Islands , 45–54 m; Indonesia, Papua, 2 m; New Caledonia, 7–22 m, Palau Islands , 45–54 m (Waller, 1972: 254 [as Juxtamusium oblectatum ]; Papua New Guinea, 20–35 m (Dijkstra, 1998a: 22). Maximum depth range of live-taken specimens is from the intertidal zone to 75 m. Present specimens from Australia alive at 12– 36 m.

Remarks. The present specimens are indistinguishable from the type material of Juxtamusium coudeini . The closely related, smaller congener Juxtamusium maldivense ( Smith, 1903) differs somewhat in having more prominent radial sculpture, which is more unevenly spaced, and in having more persistent ctenolia.

For information on functional morphology (in particular, of the left and right ctenolia and oblique resilium) see Waller (1972a: 253) and Thayer (1975: 447).

Figure 43. A, C, Gloripallium pallium (Linnaeus) , specimen in Fig. 40C, I; rv exterior (A), rv interior (C). B, E, F, H, Juxtamusium coudeini (Bavay) ; (B) specimen in Fig. 40B, rv interior; (E) specimen in Fig. 40D, lv exterior; (F, H) specimen in Fig. 40F, lv interior (F), lv exterior (H). D, Juxtamusium maldivense (Smith) , specimen in Fig.40J; rv exterior.G, J, Mirapecten moluccensis Dijkstra ,pair,WAM S43978 , SE side Scott Reef,WA, 10 m; rv exterior (G), lv exterior (J). I, K, Mirapecten rastellum (Lamarck) , rv only, AM C.153123, No Name Reef, GBR, QLD, 15–20 m; rv interior (I), rv exterior (K). Scale bars represent 30 mm (A, C), 10 mm (B, D–H, J), 20 mm (I, K).