Mirapecten tuberosus, Dijkstra & Kilburn, 2001

Dijkstra, H. H. & Kilburn, R. N., 2001, The family Pectinidae in South Africa and Mozambique (Mollusca: Bivalvia: Pectinoidea), African Invertebrates 42, pp. 263-321 : 283-285

Mirapecten tuberosus sp. n.

(Figs 16–19)

Mirapecten rastellum (non Pecten rastellum Lamarck, 1819 ); Oliver, 1992: 71, 77, textfig. 15, pl. 12, figs

6a–b.

Description: Shell height to ca. 40 mm, wider than high, triangularly orbicular, inequivalve, inequilateral, RV more convex than LV, auricles unequal, umbonal angle ca. 90–95°, preradial stage (ca. 4 mm high) smooth, microsculpture of very fine, closely spaced commarginal lamellae. LV slightly convex, with 5 primary radial plicae, covered with 3–7 tubercular spines (in early radial stage) or vesicles (in late radial stage), and 4 secondary intercostal lirae with 1–3 small tubercles. Auricles with 2 weak radial scaly riblets, on posterior more prominent. RV with 5 bipartite radial plicae and one lira near posterior margin, covered with 4–7 small vesicles, interstices smooth and rather broad. Anterior auricle with 4–6 radial riblets, absent on posterior auricle. Tubercular spines present on dorsal margin, more prominent on anterior auricle. Byssal notch deep, byssal fasciole moderately broad; active ctenolium with 6 teeth on suture. Hinge line straight. Resilifer triangular. Resilial teeth absent, dorsal teeth prominent. Auricular crura well developed. Inner surface of both valves plicate and slightly carinate near periphery. Colour uniform red, reddish-orange, orange or yellow, RV paler; interior glossy white or pigmented beyond pallial line by external coloration.

Dimensions: height 32.2 mm, length 36.9 mm, depth 11.5 mm (holotype); largest paratype 35.5 x 41.6 mm.

Type locality: off Dog Point , northern Zululand, South Africa, 27°06.5'S, 32°52.9'E, 70 m, sandstone conglomerate, live, NMDP, 4.vi.1987 .

Type material: Holotype NMSA D6476 /T1725, data as above.

Paratypes (all NMSA: NMDP, unless otherwise stated): Zululand : NE of Kosi Bay, 26°52.4'S, 32°55.2'E, 45–47 m, sand, Stn ZA 38, 3.vi.1990 (S6898/T1700: 1 LV) ; NE of Kosi Bay, 26°52.9'S, 32°55.3'E, 49 m, sand, stones, kelp, Stn ZA 41, 3.vi.1990 (S5674/

18 19

Figs 16–19. Mirapecten tuberosus sp. n. Holotype, NMSA D6476 , off Dog Point, Zululand, 70 m, pv, 32.2 x 36.9 mm. 16. LV exterior. 17. LV interior. 18. RV exterior. 19. RV interior.

T1707: 1 RV); off Kosi Bay, 26°53.8'S, 32°55.5'E, 50 m, 8.vi.1987 (D8383/T1682: PV); SE of Kosi Bay, 26°54.3'S, 32°55.5'E, 45 m, sand, stones, large algae, Stn ZA 49, 4.vi.1990 (S4865/T1714: 1 LV); off Kosi Bay, 26°54.6'S, 32°55.3'E, 50 m, medium sand, algae, Stn ZA 9, 7.vi.1987 (E519/T1715: 1 PV); off Boteler Point, 27°00.3'S, 32°55.3'E, 68 m, Stn ZB 17, 3.vi.1996 (S9703/T1713: 1 LV); off Boteler Point, 27°01.2'S, 32°54.2'E, 50 m, dead coral rubble, 6.vi.1987 [ MNHN (ex D7732): 1 LV, 1 RV; D7732/ T1702: 1 PV, 1 RV]; off Boteler Point, 27°02.6'S, 32°53.8'E, 50 m, Stn ZB 16, 6.vi.1990 (S7450/T1703: 1 LV); off Boteler Point, 27°03.7'S, 32°53.8'E, 55 m, sponges, stones, sand, Stn ZB 25, 6.vi.1990 (S6409/T1704: 1 RV); off Boteler Point, 27°04.2'S, 32°53.9'E, 58–61 m, sand, pebbles, Stn ZB 28, 6.vi.1990 (S4171/T1705: 1 LV); off Dog Point, 27°06.0'S, 32°53.3'E, 74 m, sandstone rubble, gorgonians, Stn ZC 10, 7.vi.1990 [ ZMA Moll. 3.99.002 (ex S6460): 1 PV]; off Dog Point, 27°07.6'S, 32°52.4'E, 76 m, sandstone rubble, gorgonians, Stn ZC 12, 7.vi.1990 (S8994/T1716:1 RV); SE of Rocktail Bay, 27°11.5'S, 32°50.4'E, 78 m, sandstone rocks, Stn ZD 10, 8.vi.1990 (S4634/T1681:1 RV); NE of Liefeldt’s Rocks, 27°43.4'S, 32°39.8'E, 50 m, medium sand with some stones, Stn ZJ 5, 9.vi.1988 (E3440/T1680: 1 RV); off Ledsman Shoal, 100 m, leg. A. D. Connell, 22.iv.1980 (B2665/T1701: 1 LV) .

Material examined (other than the types): SEYCHELLES: 58 m, dead coral rubble, sand, live ( HD 2676 ) ; same loc., 46 m, dead coral rubble, sand, live ( HD 2685 ) . MAURITIUS: off west coast, 40–48 m, amongst coral rubble, sand, live ( HD 2675 ) ; off west coast, 34 m, amongst coral rubble, sand, live ( HD 6589 ) . REUNION: off St. Gilles , 45–50 m, amongst coral rubble, sand, live ( HD 2680 ) .

Distribution: Tropical and subtropical western Indian Ocean, from the Red Sea and Mascarenes to northern Zululand.

Habitat: Sublittorally amongst coral or sandstone rubble on sandy bottoms; present material collected living in 34–70 m. No records are yet available from Mozambique .

Discussion: Mirapecten tuberosus most closely resembles M. mirificus (Reeve, 1853) , but differs from the latter species in its more orbicular shape, M. mirificus being more obliquely orbicular.Also, the LV in M. tuberosus is slightly convex, in M. mirificus it is flat; the posterior auricles in M. tuberosus are usually smaller than in M. mirificus ; M. tuberosus has a more prominent sculpture of scales and vesicles, and the shell is thicker; M. mirificus has a weaker sculpture of smaller erect scales, which are sometimes even absent.

Mirapecten rastellum (Lamarck, 1819) differs from M. tuberosus in its more regularly spaced radial plicae; M. tuberosus has more numerous, irregularly spaced primary and secondary radial plicae and lirae. Also, M. rastellum lacks vesicles on the plicae as found in M. tuberosus .

Mirapecten moluccensis Dijkstra, 1988 , differs from M. tuberosus in its more regularly spaced, radial plicae, which are slightly undulated or bear small tubercles. M. moluccensis has antimarginal striae near the ventral margin, which are absent in M. tuberosus . The colour pattern of M. moluccensis mainly differs from that of M. tuberosus in the presence of milky white, black or brown dots on the radial plicae; M. tuberosus is more uniform in colour.

Mirapecten yaroni Dijkstra & Knudsen, 1998 , of the Red Sea is morphologically closest to M. rastellum and differs further from M. tuberosus in its larger size (attaining 70 mm, compared with only about 35 mm in M. tuberosus ), and in its regularly spaced radial plicae which on the LV bear strongly produced lamellar scales.

M. cranmerorum (Waller, 1986) similarly differs from M. tuberosus in its larger size (attaining 70 mm high), its strongly developed and broader radial plicae, without secondary intercostal radial lirae such as occur in M. tuberosus , and in commonly possessing fine antimarginal striae near the ventral margin, which are lacking in M. tuberosus . M. cranmerorum may have a few, very weak scales on the radial plicae, but these are usually absent; M. tuberosus has strongly produced scales and vesicles on the radial plicae and intermediate lirae.

Remarks: Although Oliver (1992) figured this species as Mirapecten rastellum , it resembles neither the type specimen of Pecten rastellum Lamarck, 1819 , nor the accompanying specimen of P. rastellum ‘var. b’ of Lamarck, 1819 (see Dijkstra 1994: 474, pl. 6, figs 17–21, pl. 7, figs 22–26), as suggested by him.

Etymology: tuberosus = tuberculate, Latin, adj.