Parvamussium vidalense ( Barnard, 1964 )

Dijkstra, H. H. & Maestrati, P., 2015, Pectinoidea (Bivalvia: Propeamussiidae and Cyclochlamydidae) from the southwestern Indian Ocean, African Invertebrates 56 (3), pp. 585-585 : 614

Parvamussium vidalense ( Barnard, 1964)

Fig. 5M

Cyclopecten vidalensis Barnard, 1964: 433 , figs 14e–g. TYpe localitY: South Africa: KwaZulu­Natal: Off

Cape Vidal (NNE 1/4N, 9.5 miles), - 146–183 m, dead, dredged .

Description: Shell up to 7.3 mm in height, fragile, opaque, subcircular, almost equilateral, left valve flattened, auricles unequal in shape and size (anterior larger than posterior), umbonal angle 105°, colour whitish. Prodissoconch 200 µm long. Left valve with commarginal sculpture in early growth stage (c. 10 widely spaced delicate commarginal lamellae up to 1 mm), then radial sculpture commences (about 10 radial riblets appear and secondary intercostal ones at 2 mm), showing a latticed sculptured at the central shell disc of prominent radial ribs and overrunning commarginal lamellae, with scales on intersections.Auricles with prominent closely spaced commarginal lamellae. Hinge line straight. Inner surface with short riblets laterally (4 anteriorly, 4 posteriorly) and 2 rudimentary ventrally.

Type material examined: Holotype (lv) SAM A9495.

Other material examined: S MADAGASCAR: S Cap Sainte Marie (26°13'S 45°08'E), - 225–282 m, dead, expedition Atimo Vatae, stn CP3613, RV Nosy Bé 11, 14.v.2010 ( MNHN) .

Distribution and habitat: South Africa, off KwaZulu-Natal. Now also southern Madagascar (new record). Previously only a single left valve (holotype) at - 146– 183 m. Present left valve dead at - 225– 282 m.

Remarks:The present specimen from southern Madagascar is morphologically identical to the type specimen. Parvamussium vidalense was provisionally placed in Cyclopecten bY Barnard (1964: 433), but developed internal riblets justified placing in Parvamussium . A close congener from the SW Pacific is Parvamussium araneum Dijkstra, 1991 , which differs from P. vidalense bY having finer and more closelY spaced commarginal lamellae, more delicate radial riblets on the left valve, more spineous sculpture on the intersections, and less-developed internal riblets.

Figures

Fig. 5. Parvamussium spp.: (A–C) P. torresi (E.A. Smith, 1885): campaign Mainbaza, stn CP3143, (A) external view of the left valve, H = 7.8 mm, scale bar = 2 mm; (B) external view of the right valve, H = 6.6 mm, scale bar = 2 mm; (C) details of the left valve, H = 7.8 mm, scale bar = 0.1 mm (MNHN).(D–F) P.texturatum (Dautzenberg & Bavay, 1912):campaign Mainbaza, stn CC3151, (D) external view of the left valve, H = 5.7 mm, scale bar 2 mm; (E) external view of the right valve, H = 5.7 mm, scale bar 2 mm; (F) details of the left valve, H = 5.7 mm, scale bar 0.1 mm (MNHN). (G–I) P. vesiculatum Dijkstra, 1995: campaign Miriky, stn DW3196, (G) external view of a left valve (typical), H = 6.6 mm, scale bar = 0.2 mm; (H) external view of a left valve (atypical), H = 7 mm, scale bar = 0.2 mm; (I) details of the left valve (typical), scale bar = 0.1 mm (MNHN). (J–L) P.thyrideum (Melvill inMelvill & Standen,1907):expeditionAtimoVatae,stn DW3523,(J) external view of one left valve, H = 5.2 mm, scale bar = 1 mm (K) external view of one right valve, H = 3.1 mm, scale bar = 1 mm;; (L) details of the left valve, H = 5.2 mm, scale bar = 0.1 mm (MNHN).(M) P.vidalense (Barnard, 1964), holotype: SouthAfrica, KwaZulu-Natal, off CapeVidal, external view of the left valve, H = 7.3 mm, scale bar = 2 mm (SAM A9495).