Parvamussium vesiculatum 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 : 613-614

Parvamussium vesiculatum Dijkstra, 1995

Fig. 5G–I Parvamussium vesiculatum Dijkstra, 1995: 37 , figs 59–62, 93-96; Dijkstra & Kastoro 1997: 265, figs 95–98;

Dijkstra & Marshall 1997: 83, pl. 4, figs 11–16; Dijkstra 2001: 87; Dijkstra & Marshall 2008: 12,

figs 10F–I, 11; Dijkstra & Maestrati 2008: 96; Dijkstra & Maestrati 2009: 43, pl. 3, figs 22–24;

Dijkstra 2011: 44, pl. 1017, figs 1a–b. TYpe localitY SE New Caledonia (22°47'S 167°14'E) ,

- 440–450 m, live, 30.viii.1985 (BIOCAL, stn DW 44).

Description: Shell up to 10 mm high, fragile, semi-transparent white, almost circular, inequivalve, inequilateral, left valve slightly more convex than right, auricles unequal in shape and size, umbonal angle 95°–105°. Inner surface with rudimentary riblets anteriorly and posteriorly, also weak on auricles. Prodissoconch 200 µm long. Left valve sculptured with widely spaced commarginal lirae with strongly developed, radially arranged nodules or hollow scales on intersections of commarginal and radial sculpture. Unevenly spaced radial riblets between commarginal lirae. Auricles with commarginal lamellae, prominent on anterior, slightly closer on posterior. Hinge line straight. Right valve with evenly spaced commarginal lirae, weak near umbonal region. Prodissoconch pellucid.Anterior auricle with 4 delicate radial riblets with commarginal lamellae continuing over them uninterrupted, developed into scales on dorsal margin. Byssal notch shallow, byssal fasciole narrow.

Type material examined: Holotype (pr) MNHN Moll 21167. Paratypes (36 pr + 27 v): 2 AMS C.201715, 12 ZMA Moll. 395030, 43 MNHN Moll 21168, 2 NMNZ M.268538, 2 NSMT-Mo 70542, 2 USNM 890874. Other material examined:NW MADAGASCAR: West of Cap d’Ambre (12°08'S 48°56'E), - 238–249 m, dead, campaign Miriky, stn DW3196, 28.vi.2009 ( MNHN) . S MADAGASCAR: Manantenina (24°23'S 47°31'E), - 200–220 m, live, expedition Atimo Vatae, stn DW3523, RV Nosy Bé 11, 01.v.2010 ( MNHN) ; Manantenina (24°23'S 47°32'E), - 307–319 m, dead, expedition Atimo Vatae, stn DW3524, RV Nosy Bé 11, 01.v.2010 ( MNHN) ; Manantenina (24°24'S 47°33'E), - 402–407 m, dead, expedition Atimo Vatae, stn DW3529, RV Nosy Bé 11, 01.v.2010 ( MNHN) ; S of Faux Cap (26°07'S 45°39'E), - 264–280 m, dead, expedition Atimo Vatae, stn DW3552, RV Nosy Bé 11, 05.v.2010 ( MNHN) ; S of Faux Cap (26°08'S 45°39'E), - 280–333 m, dead, expedition Atimo Vatae, stn DW3553, RV Nosy Bé 11, 05.v.2010 ( MNHN) ; 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) ; S Cap Sainte Marie (26°13'S 45°08'E), - 250–300 m, dead, expedition Atimo Vatae, stn CP3614, RV Nosy Bé 11, 14.v.2010 ( MNHN) .

Distribution and habitat: Southwestern Pacific from Taiwan southwards to Australia, eastwards to Tonga ( Dijkstra & Maestrati 2008: 96), now also extended into the southwestern Indian Ocean from northwestern and southern Madagascar (new record). Living bathyally on soft substrata of mud and sand at - 205– 650 m. Present specimens live at - 200– 220 m.

Remarks: The present specimens from northwestern and southern Madagascar are morphologically identical to the type material, although one left valve is almost smooth and transparent and another left valve almost lacks the typical hollow scales on the intersections and has prominent internal ribs, which commence in early ontogeny. However, these characters are strongly variable and similar specimens are examined in material from the southwestern Pacific (MNHN).

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).