Cyclopecten cassiculus, Dijkstra & Maestrati, 2015

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 616-617

Cyclopecten cassiculus sp. n.

Fig. 6A–G

Etymology: From the Latin cassiculus (m.) (small spider’s web), after the sculpture of left valve that resembles a spider’s web with fine raindrops on the intersections.

Description: Shell up to 8.9 mm in height, fragile, lv opaque, rv semi-transparent, somewhat higher than wide, inequivalve, flattened and somewhat rough, left valve slightlY more convex than right valve, inequilateral, anterior auricle larger than posterior, umbonal angle 90°–95°, colour of left valve creamy, right valve whitish. Prodissoch 170 µm long. Left valve sculptured with very closely spaced commarginal lirae in early growth stage (c. 10 per mm), more prominent and widely spaced on central shell disc (c. 4–5 per mm), 8–10 fine radial lirae commence c. 0.8–1.0 mm below umbo, increasing to c. 15 strong primary lirae near periphery with interstitial secondary lirae, intersections with small nodules on primary radial lirae in early growth stage, more lamellar in adult stage, small nodules on secondary interstitial riblets, similar sculptured auricles almost continuous with shell disc. Right valve with very weak, regularly spaced, delicate commarginal lamellae (c. 10 per mm). Anterior auricle with 6–7 antimarginal noduliferous lirae, posterior auricle continuous with disc with verY fine and close-set commarginal lirae. Byssal notch moderately deep, byssal fasciole rather small, no ctenolium. Hinge line straight. Resilifer triangular. Internal ribs lacking.

Dimensions (holotype): height 8.9 mm, width 8.0 mm, convexity 2.9 mm.

Type material: Holotype, pr ( MNHN IM-2007-41951), paratype, pr ( MNHN IM-2007-41954).Type locality: MADAGASCAR: Near Mahajamba Bay (14°50'S 46°57'E), - 340–446 m, live, campaign Miriky, stn CP3248, RV Miriky, leg. P. Bouchet & Y. Kantor, 07.vii.2009.

Paratype: MADAGASCAR: Between Majunga and Cap Saint-André (15°32'S 45°45'E), - 327–730 m, live, campaign Miriky, stn CP3265, RV Miriky, leg. P. Bouchet & Y. Kantor, 10.vii.2009 .

Distribution and habitat: NW Madagascar, living upper bathyally at - 327–340 m (minimum depth range).

Remarks: The closest resembling species is Parvamussium cassium Dijkstra, 1991 , recorded from deep water (- 450–600 m) off Indonesia. Cyclopecten cassiculus morphologically differs from P. cassium bY having prominent radial and fine commarginal lirae (in P. cassium weaker and more equal of prominence), in having secondary intercostal radial lirae in late ontogeny ( P. cassium in earlier growth stage), in having fine interstitial radial lirae, up to 6 near ventral margin (one radial lira in P. cassium ), and in having coarser nodules and lamellae on intersections of lirae ( P. cassium very small nodules). Both species are lacking internal ribs, although P. cassium has a short auricular riblet (very weak in the present species).

A somewhat resembling species is Parvamussium vidalense ( Barnard, 1964) , recorded from eastern South Africa and herein also from southern Madagascar. This species has a reticular sculpture on the left valve of more closelY spaced, finer radial and commarginal lirae with short spines or curved lamellae on the radial and commarginal intersections. Moreover, several rudimentary interior ribs are present (lacking in C. cassiculus ).

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).