Semipallium crouchi (E. A. Smith, 1892)

Dijkstra, H. H. & Kilburn, R. N., 2001, The family Pectinidae in South Africa and Mozambique (Mollusca: Bivalvia: Pectinoidea), African Invertebrates 42, pp. 263-321 : 296-297

Semipallium crouchi (E. A. Smith, 1892)

(Figs 33–34)

Pecten crouchi E. A. Smith, 1892: 255 , fig. Type locality: Mauritius.

Chlamys (Manupecten) crouchi crouchi ; Eames & Cox, 1956: 48.

Semipallium crouchi ; Wagner, 1989: 112, 115, fig. 9 (holotype); Dijkstra & Knudsen, 1998: 80, pl. 6, fig. 29

(further references, type data, distribution, discussion).

Description: Shell height to 60 mm (average ca. 40 mm); moderately convex, LV more so than RV, elongate, slightly oblique, inequilateral, auricles very unequal, umbonal angle ca. 80–85°. LV with 7 prominent radial costae, plus one narrow costa on each anterior and posterior margin; costae narrower than their intervals. Secondary radial riblets are developed on costae and in the intervals, sometimes almost invisible due to the surficial shagreen microsculpture. Anterior auricle larger than posterior (ca. 2.5:1), sculptured with ca. 10 irregularly placed radial riblets, posterior auricle with 3–5. RV with 8 prominent radial costae, broader than their intervals. Secondary riblets and microsculpture as on LV. Anterior auricle sculptured with 6–8 irregularly placed radial riblets, posterior with 2–3. Hinge line straight, except on postero-dorsal margin (slightly inclined). Antero-dorsal margin pustular or tubercular. Byssal fasciole relative small, byssal notch shallow. Active ctenolium with 5–7 teeth on suture. Resilifer elongate, obliquely triangular. Auricular crura rather small. Inner surface strongly plicated, semitransparent, and yellowish near ventral margin. Colour cream with brown or purple markings.

Type material: see Dijkstra & Knudsen (1998).

Regional data: SOUTH AFRICA: Zululand: off Rocktail Bay, 75 m, sandstone rubble, live (D6372).

33 34

Figs. 33–34. Semipallium crouchi (Smith, 1892) : NMSA D6372 , off Rocktail Bay, Zululand , 75 m, pv, 25.0 x 21.8 mm. 33. LV exterior. 34. RV exterior .

Distribution: Tropical western Indian Ocean from the Red Sea to northern Zululand ( South Africa) and Rèunion Is.

Habitat: Usually living littorally or in shallow water amongst coral rubble or under coral boulders on sandy bottoms.

Remarks: The present specimen resembles the holotype of S. crouchi , and is a new record for South Africa. Another tropical Indo-Pacific species, Semipallium dianae ( Crandall, 1979) closely resembles S. crouchi , but differs slightly in ribbing (sometimes with one additional rib) and in coloration (brighter and more variable).