Cyclopecten horridus Dijkstra, 1995

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 617-618

Cyclopecten horridus Dijkstra, 1995

Fig. 6H–I

Cyclopecten horridus Dijkstra, 1995: 41 , figs 63–64, 98; Dijkstra & Marshall 1997: 87; 2008: 16, 12E –H,

13. Type locality: Loyalty Islands, 20°29'S 166°43'E, - 600 m, live, RV Alis, leg. P. Bouchet , B.

Métivier & B. Richer de Forges-IRD, 16.02.1989 (MUSORSTOM 6, stn DW 420).

Description: Shell up to 6 mm in height, fragile, circular, inequivalve, almost equilateral, left valve more inflated than right valve, auricles nearlY equallY sized, umbonal angle 120°–125°, colour dull whitish. Prodissoconch 170 µm long. Left valve sculptured with regularly spaced commarginal lamellae, close-set in early growth stage, enlarging towards periphery. Prominent hemitubular scales on commarginal lamellae arranged in radial rows that multiplY bY intercalation (Dijkstra & Marshall 2008: figs 12E, 12H). Auricles similar sculptured and continuous with shell disc. Right valve with regularly arranged closely spaced commarginal lirae sculptured with delicate spines near ventral margin. Anterior auricle with 3 radial riblets and overrunning commarginal lamellae. Posterior auricle almost continuous with shell disc with commarginal lirae. Hinge line straight. Antero-dorsal margin with scales, squamae weakly on postero-dorsal margin. Byssal notch strongly developed.

Type material examined: Holotype, pr ( MNHN IM-2000-21163).

Other material examined: SOUTH AFRICA: Transkei : Off Whale Rock (32°01.3'S 29°19.3'E), - 150–200 m, dead, sponge rubble, NMDP stn M8, dredged RV Meiring Naudé, 20.vii.1982 ( NMSA E65 ) .

Distribution and habitat: New Caledonia, Loyalty Islands and Kermadec Ridge (Dijkstra & Marshall 2008: 16). Now also from off Transkei, South Africa (new record). Live at - 350– 600 m. Present specimens dead at - 150– 200 m.

Remarks: The present specimens are almost indistinguisable from the type material. The hemitubular scales on the commarginal lirae of the left valve are coarser and more widely spaced. However, intermediate variations are also observed from the southwestern Pacific (MNHN). Other morphological characters are similar.

Cyclopecten erythraeensis Dijkstra & Janssen, 2013 , recently recorded from the Red Sea, differs from C. horridus by having a more closely spaced and delicate commarginal sculpture on the left valve with finer and less-hemitubular scales.

Figures

Fig. 6. Cyclopecten spp.: (A–G) C. cassiculus sp. n., holotype: campaign Miriky, stn CP3248, (A) external view of the left valve, H = 8.5 mm, scale bar = 2 mm; (B) internal view of the left valve,H = 8.5 mm, scale bar = 2 mm; (C) external view of the right valve, H = 7 mm, scale bar = 2 mm; (D) internal view of the right valve, H = 7 mm, scale bar = 2 mm; (E) prodissoconch of the left valve, H = 8.5 mm, scale bar = 0.1 mm; (F) details of the left valve, H = 8.5 mm, scale bar = 0.1 mm; (G) details of the right valve, H = 7 mm, scale bar = 0.1 mm (MNHN 41951). (H, I) C. horridus Dijkstra, 1995: South Africa, Transkei, off Whale Rock, (H) external view of the left valve, H = 3.3 mm, scale bar = 1 mm; (I) details of the left valve, H = 3.3 mm, scale bar = 0.1 mm (NMSA E65).