Parvamussium puillandrei, 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 : 604-605

Parvamussium puillandrei sp. n.

Fig. 2H–N

Etymology: After Dr Nicolas Puillandre, Assistant Professor at the MNHN and participant in the present campaign.

Description: Shell up to 12.9 mm in height, fragile, inequivalve, inequilateral, somewhat higher than wide, left valve slightlY more inflated than right valve, whitish, auricles almost equal in size, relatively small, umbonal angle c. 90°. Prodissoconch 210 µm long. Left valve with prominent commarginal lamellae, commencing c. 0.5 mm below the umbonal top and covering the shell disc (c. 6–7 per mm on central part of disc) towards the ventral margin, crossing c. 10–15 irregularly spaced radial costae in early growth stage, commencing c. 2 mm below the umbonal top, increasing by interstitial secondary radial riblets towards the ventral margin to c. 30 in number.Auricles with closely spaced commarginal lamellae, which is somewhat more prominent on the anterior auricle. Hinge line straight. Right valve with regularly spaced slightly undulated commarginal lirae, weak in earlY ontogenY, more prominent laterallY, covered with radiallY arranged fine vesicular sculpture. Anterior auricle well developed, sculptured with 6–7 fine radial riblets, covered with commarginal lamellae, which are strongly developed on antero-dorsal margin. Posterior auricle covered with commarginal lamellae, which are more prominent on postero-dorsal margin. Marginal apron broken off in all specimens seen. Internal lirae 10, 3 of them rudimentary, plus 1 small posterior auricular lira on the left valve; 9 lirae plus 3 rudimentary, and 1 posterior auricular lira on right valve. Lirae commencing in early growth stage and enlarging towards the submarginal area (c. 3 mm from the periphery). Exterior sculpture of left valve slightly visible from the interior. Outer ligament small. Resilifer triangular. Byssal notch small. Fasciolar pseudo-ctenolium lacking. Dimensions: Holotype: Height 12.9 mm, width 12.3 mm, convexity 3.0 mm.

Type material: Holotype, pr ( MNHN IM-2007-39021), paratypes ( MNHN IM-2007-39051, 1 pr; MNHN IM-2007-39296, 1 pr; MNHN IM-2000-30116, 2 lv). Type locality: NW MADAGASCAR: West of Cap d’Ambre (12°06'S 48°54'E), - 560–653 m, live, campaign Miriky, stn DW3200, 28.vi.2009.

Other material examined: S MADAGASCAR: Manantenina (24°24'S 47°33'E), - 424–438 m, dead, expedition Atimo Vatae, stn DW3528, RV Nosy Bé 11, 01.v.2010 ( MNHN, 2 lv) ; E of Faux Cap (25°37'S 46°20'E), - 433–456 m, live, expedition Atimo Vatae, stn DW3564, RV Nosy Bé 11, 06.v.2010 ( MNHN, 21 pr, 1 lv) ; E of Faux Cap (25°36'S 46°21'E), - 618–624 m, dead, expedition Atimo Vatae, stn DW3565, RV Nosy Bé 11, 06.v.2010 ( MNHN, 1 lv) ; E of Faux Cap (25°37'S 46°21'E), - 618–624 m, dead, expedition Atimo Vatae, stn CP3566, RV Nosy Bé 11, 06.v.2010 ( MNHN, 1 rv); S Pointe Barrow (25°32'S 44°16'E), - 549–576 m, live, expedition Atimo Vatae, stn CP3585, RV Nosy Bé 11, 10.v.2010 ( MNHN, 1 pr, 5 lv, 7 rv) .

Distribution and habitat: To date northwestern and southern Madagascar. Living bathyally on soft substrata of mud and sand at a minimum depth range of - 456– 560 m. Remarks: The onlY closelY resembling congeneric species from the Indo-Pacific is Parvamussium undisonum Dijkstra, 1995 , recorded from the southwestern Pacific ( Dijkstra & Maestrati 2008: 96), live at - 431– 710 m. However, P. puillandrei differs morphologically from P. undisonum in having a more closely spaced commarginal sculpture ( P. puillandrei 6–7 per mm, P. undisonum 5 per mm in the central shell disc) on both valves, in having more and stronger developed radial ribs on the left valve ( P. puillandrei up to c. 20, P. undisonum up to c. 15) and more interstitial secondary radial riblets, in having a broader groove between the disc and the anterior auricle of the right valve ( P. undisonum narrow), in lacking a pseudo-ctenolium (which is present in adult P. undisonum ), and in having earlier developed internal ribs (internal ribs in P. undisonum commence in a later growth stage near the adductor insertion scar).

The pseudo-ctenolium, an unusual character in Propeamussiidae , is discussed by Waller (1984: 213, figs 5a–b) in Parvamussium sayanum (Dall, 1886) , known from the tropical western Atlantic, and this feature is also observed in adult specimens of P. undisonum , lacking in the present species.

Figures

Fig.2. Parvamussium spp.:(A–G) P.catillus sp.n., holotype:campaign Mainbaza, stn CP3139, (A) external view of the left valve, H = 7.2 mm, scale bar = 2 mm; (B) internal view of the left valve,H = 7.2 mm, scale bar = 2 mm; (C) external view of the right valve, H = 7.2 mm, scale bar = 2 mm; (D) internal view of the right valve, H = 7.2 mm, scale bar = 2 mm; (E) details of the left valve, H = 7.2 mm, scale bar = 0.1 mm; (F) details of the right valve, H = 7.2 mm, scale bar = 0.1 mm; (G) prodissoconch of the left valve,H = 7.2 mm,scale bar = 0.2 mm (MNHN 41966).(H–N) P.puillandreisp.n., holotype: campaign Miriky, stn DW3200, (H) external view of the left valve, H = 12.4 mm, scale bar = 0.2 mm; (I) internal view of the left valve, H = 12.4 mm, scale bar = 0.2 mm; (J) external view of the right valve, H = 10 mm, scale bar = 0.2 mm; (K) internal view of the right valve, H = 10 mm, scale bar = 0.2 mm; (L) prodissoconch of the left valve, H = 12.4 mm, scale bar = 0.2 mm; (M) details of the right valve, H = 10 mm, scale bar = 0.1 mm; (N) details of the left valve, H = 10 mm, scale bar = 0.1 mm (MNHN 39021).