Parvamussium kilburni, 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 : 602-604

Parvamussium kilburni sp. n.

Fig. 3C–I

Etymology:After the late Dr Richard (Dick) Neil Kilburn, formerly Head of the Department of Mollusca at the KwaZulu-Natal Museum, Pietermaritzburg, South Africa.

Description: Shell up to 12 mm in height, fragile, semi-transparent, subcircular, somewhat higher than wide, inequivalve, left valve slightly more convex than right valve, equilateral, auricles unequal, umbonal angle 100°–105°, colour of left valve creamy and reddish mottled, right valve transparent whitish. Prodissoconch 170 µm long. Left valve smooth on central part of shell disc, umbonal part glossy, sculptured with very closely spaced (c. 15 per mm) fine commarginal lamellae near ventral margin, verY weak and fine radial sculpture postero-laterallY, in most specimens lacking. Anterior auricle larger than posterior and sculptured with fine, close-set commarginal lamellae, posterior auricle smooth or very weakly sculptured with antimarginal lirae. Right valve with very weak, regularly spaced, commarginal lirae (c. 10 per mm). Anterior auricle with fine antimarginal lirae and verY weak commarginal lirae near dorsal margin, posterior auricle with verY fine and close-set commarginal lirae. BYssal notch moderatelY deep,

byssal fasciole rather small, no ctenolium. Hinge line straight. Resilifer triangular. Internal prominent ribs 10 or 11, in adult specimens with 1–5 rudimentary interstitial riblets near ventral margin and one auricular riblet anteriorly and posteriorly. Internal ribs commencing in early growth stage, extending to marginal area.

Dimensions (holotype): Height 11 mm, width 10 mm (part of margin broken off), convexity 2.2 mm.

Type material: Holotype (pr) NMSA D7689. Type locality: SOUTH AFRICA: Zululand : Off Dog Point (27°07.0'S 32°54.1'E), - 250 m, live, medium sand, NMDP stn ZC7, dredged RV Meiring Naudé, 04.vi.1987 . Paratypes: SOUTH AFRICA: Zululand: Off Dog Point (27°07.0'S 32°54.1'E), - 250 m, live, medium sand, NMDP stn ZC7, dredged RV Meiring Naudé, 04.vi.1987 ( NMSA D7689 , 2 lv) ; Off Dog Point (27°07.3'S 32°53.6'E), - 200 m, live, fine sand, NMDP stn ZC6, dredged RV Meiring Naudé, 04.vi.1987 ( NMSA D7773 , 2 pr, 3 lv, 2 rv) ; NE of du Leven Point (27°54.8'S 32°38.5'E), - 170 m, dead, sandstone rubble, coarse sand, NMDP stn ZL4, dredged RV Meiring Naudé, 09.vi.1988 ( NMSA E3705 , 3 lv, 2 rv) ; Off Cape Vidal (28°08.4'S 32°36.4'E), - 165 m, dead, moderatelY fine sand, NMDP stn ZM8, dredged RV Meiring Naudé, 11.vi.1988 ( NMSA E3789 , 3 lv, 15 rv) ; Off Mission Rocks (28°17.4'S 32°34.6'E), - 198 m, dead, medium sand, NMDP stn ZN6, dredged RV Meiring Naudé, 11.vi.1988 ( NMSA E4757 , 5 lv, 5 rv) ; SE of Neill Peak ( Cunge ) (28°44.2'S 32°23.0'E), - 260–280 m, dead, muddy sand, NMDP stn ZP4, dredged RV Meiring Naudé, 12.vi.1988 ( NMSA E4084 , 1 lv) ; KwaZulu­Natal: Off Durban (29°53.2'S 31°11.2'E), - 165 m, dead, fine muddy sand, corals, NMDP stn XX14, dredged RV Meiring Naudé, 16.vi.1983 ( NMSA B5895 , 1 lv) ; Off Umlaas Canal (30°02.2'S 31°03.1'E), - 200 m, dead, coarse sand, NMDP stn XX69, dredged RV v, 09.vii.1985 ( NMSA D882 , 1 lv) ; Off Umlaas Canal (30°02.2'S 31°03.9'E), - 250 m, dead, coarse sand, NMDP stn XX68, dredged RV Meiring Naudé, 09.vii.1985 ( NMSA D936 , 10 lv, 9 rv) ; Off Amanzimtoti (30°04.7'S 31°03.3'E), - 300–305 m, dead, medium sand, NMDP stn XX66, dredged RV v, 09.vii.1985 ( NMSA D1302 , 1 lv, 6 rv) ; Off Amanzimtoti (30°05.3'S 31°02.5'E), - 260–270 m, dead, medium sand, NMDP stn XX65, dredged RV Meiring Naudé, 09.vii.1985 ( NMSA D1173 , 8 lv, 7 rv) ; Off Amanzimtoti (30°05.6'S 31°00.6'E), - 180 m, dead, medium sand, NMDP stn XX63, dredged RV Meiring Naudé, 09.vii.1985 ( NMSA D1233 , 5 lv, 4 rv) ; Transkei: Off Mgazi River (31°44.3'S 29°32.2'E), - 250 m, dead, muddy sand, dredged, 04.vii.1985 (RV Meiring Naudé, stn J11) ( NMSA C8924 , 1 lv) ; Off Whale Rock (32°00.9'S 29°21.8'E), - 400–420 m, dead, coarse sand, old shell debris, stones, dredged, 20.vii.1982 (RV Meiring Naudé, stn M7) ( NMSA C2063 , 2 lv, 2 rv) ; Off Mbashe River (32°21.2'S 29°01.4'E), - 295–300 m, dead, old shell rubble, NMDP stn Q15, dredged RV Meiring Naudé, 06.vii.1985 ( NMSA C8984 , 1 lv) .

Distribution and habitat: South Africa, from Zululand southwards to Transkei (27°S – 32°S), living upper bathyally on sandy bottoms at - 200– 250 m.

Remarks: The closest resembling species is Parvamussium virgatum Dijkstra, 1991 , recorded from Indonesia, Solomon Islands and Wallis and Futuna ( Dijkstra & Maestrati 2008: 97). Parvamussium kilburni differs morphologically from P.virgatum by a smooth or very weakly commarginal sculptured disc shell of the left valve ( P. virgatum with fine radial sculpture), bY having more prominent developed interior ribs, commencing earlier and extending to the periphery ( P. virgatum with finer, commencing in late growth stage and extending to the submarginal area).

Another closely resembling species is Parvamussium formosum (Melvill in Melvill & Standen, 1907), recorded from the northwestern Indian Ocean.This species has prominent radial and commarginal sculpture commencing in early growth stage on the left valve ( P. kilburni lacks radial sculpture and has a commarginal sculpture only developed marginally in late ontogeny). Parvamussium formosum has also more prominent interior ribs with more interstitial rudimentary riblets (up to 7) in adult specimens.

Figures

Fig.3. Parvamussiumspp.: (A, B, J, K) P.formosum (Melvill inMelvill &Standen,1907):campaign Miriky, stn CP3228, (A) external view of the left valve, H = 9 mm, scale bar = 2 mm; (B) external view of the right valve, H = 7.8 mm, scale bar = 2 mm; (J) details of the left valve, campaign Miriky, stn CP3228, H = 9 mm, scale bar = 0.1 mm; (K) details of the right valve, H = 7.8 mm, scale bar = 0.1 mm (MNHN). (C–I) P. kilburni sp. n., holotype: N. Zululand, off Dog Point, (C) external view of the left valve, H = 10.5 mm, scale bar = 2 mm; (D) external view of the right valve, H = 9.1 mm, scale bar = 2 mm; (E) internal view of the left valve, H = 10.5 mm, scale bar = 2 mm; (F) internal view of the right valve, H = 9.1 mm, scale bar = 2 mm; (G) prodissoconch of the left valve, H = 10.5 mm, scale bar = 0.2 mm; (H) details of the left valve, H = 10.5 mm, scale bar = 0.1 mm; (I) details of the right valve, N. Zululand, off Dog Point, H = 10.5 mm, scale bar = 0.1 mm (NMSA D7689).