Decatopecten amiculum ( Philippi, 1851 )

Dijkstra, H. H. & Kilburn, R. N., 2001, The family Pectinidae in South Africa and Mozambique (Mollusca: Bivalvia: Pectinoidea), African Invertebrates 42, pp. 263-321 : 276-277

Decatopecten amiculum ( Philippi, 1851)

(Figs 10–11)

Pecten amiculum Philippi, 1851: 89 . Type locality: Madagascar (Malagasy Republic).

Decatopecten amiculum ; Dijkstra & Knudsen, 1998: 55, pl. 5, fig. 25, pl. 9, figs 42–43 (references and synonymy, type data, distribution).

Description: Shell up to 45 mm high, usually ca. 30–35 mm, solid, suborbicular, RV slightly more convex than LV, equilateral, auricles small and subequal, umbonal angle 90–95°. Both valves laterally compressed, sometimes tumid or commarginally inflated by growth interruptions, with several radial plicae (7–11), radially striated, also on interspaces. Microsculpture of closely spaced commarginal lamellae. Hinge small, straight. Byssal fasciole small or absent, byssal notch weak. Active ctenolium with few rudimentary teeth (to 5) on suture, sometimes absent; inactive ctenolium present. Resilifer elongate, triangular. Auricular crura strongly developed; resilial teeth weak or absent. Inner surface slightly plicated. Colour variable, whitish, creamy, yellowish or brownish with lighter or darker blotches or irregular concentric markings, sometimes almost uniform in colour; RV paler.

Type material: see Dijkstra & Knudsen (1998).

Regional data: MOZAMBIQUE: Moçimboa da Praia, living (NMSA G4952: A. Ramalho); Quirimba Island, sandbanks among Thalassodendron (NMSA J8618: RK); Nacala, Fernão Veloso, 15 m, sandy bottom with rocks, live (HD6621); NE Nacala Bay, off Chalau, in Thalassodendron with gravel, dead (NMSA H4482: K. J. Grosch); Lunga Bay, off Puieirua, 0.3 m below LST, on Thalassodendron , gravel (NMSA H4490: K. J. Grosch); same loc., in Thalassodendron on gravel, 0.3 m below LST (NMSA H4480: K. J. Grosch); Conducia Bay, dead (NMSA H4491: K. J. Grosch); SW Conducia Bay, 1.2 m below LST, in Thalassodendron , muddy, dead (NMSA H4479: K. J. Grosch); same loc., sandflats, on Thalassodendron , dead (NMSA H4475: K. J. Grosch); same loc., 1.2 m below LST, on small rock in Thalassodendron , dead (NMSA H4476: K. J. Grosch); Mozambique Bay, S Sancul, 1 m below LST, in Thalassodendron with gravel, dead (NMSA H4478: K. J. Grosch); Mozambique Is., Thalassodendron and gravel, 0.3 m below LST (NMSA H4480: K. J. Grosch); Inhambane (NMSA G3761: B. J. Young). SOUTH AFRICA: Zululand (all NMSA: NMDP): off Kosi Bay, 40 m, shell rubble, dead (D7973); SE of Kosi Bay, 40 m, shell rubble, dead (D8138); same loc., 50 m, fine, slightly muddy sand, dead (D8326).

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

Habitat: Living free amongst coral rubble or on muddy, sandy or muddy sand bottoms at littoral to sublittoral depths. In Mozambique often living amongst the marine grass Thalassodendron .

Remarks: D. amiculum differs from the better-known D. plica (below) mainly in its more numerous (7–11, against 3–5), equally-strong radial plicae, and usually in its more compressed valves. However, radial striae and commarginal lamellae are similar. The two species appear to be syntopic.