Juxtamusium maldivense (E. A. Smith, 1903)

Dijkstra, H. H. & Kilburn, R. N., 2001, The family Pectinidae in South Africa and Mozambique (Mollusca: Bivalvia: Pectinoidea), African Invertebrates 42, pp. 263-321 : 281-282

Juxtamusium maldivense (E. A. Smith, 1903)

(Figs 14–15)

Pecten maldivensis E. A. Smith, 1903: 622 , pl. 36, figs 19–20. Type locality: Suvadiva Atoll, Maldive

Islands, Indian Ocean, 7–80 m.

Juxtamusium maldivense ; Dijkstra, 1984: 8, fig.; idem, 1991: 47; idem, 1998: 23, pl. 3, figs 1–3; Rombouts,

1991: 60, pl. 26, fig. 7; Dijkstra & Knudsen, 1998: 64, pl. 5, fig. 22 (further references, type data,

distribution, discussion).

Description: Shell thin, height to 25 mm (average ca. 15 mm), compressed, suborbicular, higher than wide, slightly equilateral, auricles unequal, umbonal angle ca. 90°. Both valves slightly convex, RV somewhat more so than LV, with numerous fine, irregularly spaced, angular radial riblets, increasing by bifurcation and/or intercalation, and microscopic very closely spaced commarginal lamellae. Posterior auricle larger than anterior, with ca. 3–7 radial riblets, sometimes very weak. Hinge straight. Byssal fasciole narrow, byssal notch shallow. Ctenolium present along suture in both valves. Resifer

14

15

Figs 14–15. Juxtamusium maldivense (Smith, 1903) : HD 2734 (ex NMSA D8069), SE of Kosi Bay, Zululand, 65 m, pv, 23.0 x 21.2 mm. 14. LV exterior. 15. RV exterior.

oblong and oblique.Auricular crura weak. Inner surface somewhat plicated near ventral margin. Colour variable, cream to pink, with shades of red or brown and lighter and darker blotches, interior purple or reddish, RV paler; sometimes more uniform in colour.

Type material: see Dijkstra & Knudsen (1998).

Regional data: SOUTH AFRICA: Zululand (all NMSA: NMDP, selected records only): off Kosi Bay , 50 m, medium sand, algae, live (D6888); SE of Kosi Bay, 50 m, medium sand and algae, live (D6253); same loc., 65 m, sponge, gorgonians, medium sand, live (D8069); same loc., 48 m, sand and rubble, live (D8716); off Jesser Point, 70 m, medium sand, dead (D8450); off Boteler Point, 50 m, coral, sponges, live (D6839); same loc., 50 m, coral rubble, live (D7741); same loc., 78 m, marine growths, dead (S6649); same loc., 53 m, lithothamnial pebbles, sand, dead (S6875); same loc., 50 m, coral rubble, lithothamnion, live (D7429); same loc., 50 m, coral rubble, lithothamnion, dead (D9204); NE of Dog Point, 56–57 m, sand, lithothamnial pebbles, live (S5050); NE of Liefeldt’s Rocks, 50 m, lithothamnion, medium sand, dead coral rubble, dead (E4319); same loc., 50 m, lithothamnion stones, coarse sand, live (E4400) .

Distribution: Throughout tropical Indo-West Pacific (except Hawaii and Polynesia), south-western limit northern Zululand.

Habitat: Living byssally attached to coral branches, under rocks or between coral rubble on sandy bottoms at littoral to sublittoral depths.

Remarks: Juxtamusium coudeini ( Bavay, 1903) , its only congener, is morphologically very similar but attains a somewhat larger size (to ca. 30 mm high), with fewer, more regularly spaced, rounded radial riblets. For more information on functional morphology and ecology see Waller (1972: 253). Present specimens from South Africa are similar to the type material, although the angular radial riblets are slightly more prominent.