Parvamussium catillus, 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 : 599-601

Parvamussium catillus sp. n.

Fig. 2A–G

Etymology: From the Latin catillus (m.) (small dish), after the smooth circular shell that resembles a small dish.

Description: Shell up to 7.2 mm in height, fragile, semi-transparent, circular, inequivalve, left valve slightlY more inflated than right valve, equilateral, auricles almost equal in size, umbonal angle 110°–115°, colour whitish. Prodissoconch 100 µm long. Left valve smooth and dead throughout shell disc, umbonal part glossy and transparent. Anterior auricle with very weak and delicate widely spaced commarginal lamellae, more prominent near shell disc, posterior auricle almost smooth with traces of very closely spaced commarginal lirae laterally. Right valve with weak, regularly spaced, commarginal lirae (c. 8 per mm).Anterior auricle with weak and verY fine commarginal lirae and a noduliferous ridge along the byssal fasciole, posterior auricle continuous with disc, smooth with very close-set commarginal lirae laterally. Byssal notch moderately deep, byssal fasciole rather small, no ctenolium. Hinge line straight. Resilifer triangular. Internal ribs 13 commence in early growth stage and are exposed almost to the periphery, one interstitial rudimentary riblet antero-ventrally, and one riblet on both auricles.

Dimensions (holotype): Height 7.2 mm, width 7.2 mm, convexity 2.5 mm.

Type material: Holotype (pr) ( MNHN IM-2007-41966), paratype (pr) ( MNHN IM-2007-41964). Type locality: MOZAMBIQUE CHANNEL: Inhambane transect (23°35'S 36°06'E), - 1092–1195 m, live, campaign Mainbaza, stn CP3139, RV Vizconde de Eza , leg. P. Bouchet, J. Rosado & E. Strong, 11.iv.2009.

Distribution and habitat: See type locality.

Remarks: The closest resembling species is Parvamussium multiliratum Dijkstra, 1995 , recorded from New Caledonia, Vanuatu, Fiji, Tonga, Wallis and Futuna (Dijkstra & Maestrati 2012: 392). Parvamussium catillus morphologically differs from P. multiliratum by a smooth shell disc of the left valve ( P. multiliratum with prominent commarginal lamellae and weak radial sculpture postero-laterally), by having fewer interior ribs ( P. multiliratum 14 and two rudimentary).

Another somewhat resembling species is Propeamussium arabicum Dijkstra & Janssen, 2013 , recorded from the Gulf of Aden and herein also from northwestern Madagascar and the Mozambique Channel. This species is also circular in shape, but larger sized (up to 14.9 mm in height, P. catillus up to 7.2 mm) and has a fine reticular sculpture on the left valve ( P. catillus smooth). Moreover, fewer internal ribs (7 without rudimentary, P. catillus 13 and one rudimentary).

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).