Parvamussium marquesanum, Dijkstra & Maestrati, 2008

Dijkstra, Henk H. & Maestrati, Philippe, 2008, New species and new records of deep-water Pectinoidea (Bivalvia: Propeamussiidae, Entoliidae and Pectinidae) from the South Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 77-114 : 89-91

Parvamussium marquesanum n. sp.

Figs 20-25

TYPE MATERIAL. — Holotype (spm) MNHN 20455 and 8 paratypes MNHN 20456-20458 , 1 HD.

TYPE LOCALITY. — Marquesas Islands, Eiao , 07˚55’S, 140˚44’W, 660-680 m [MUSORSTOM 9: stn CP 1272] .

MATERIAL EXAMINED. — Marquesas. MUSORSTOM 9: stn CP 5 spms (holotype MNHN 20455 and 3 paratypes MNHN 1271 , 07 ˚54’S, 140˚42’W, 600 m, 2 spms, 1 lv, 1 rv (paratypes 20457, 1 HD); stn CP 1307, 08˚58’S, 140˚16’W, 708-738 m, MNHN 20456 ); stn CP 1272, 07˚55’S, 140˚44’W, 660-680 m, 1 spm (paratype MNHN 20458 ) .

DISTRIBUTION. — Marquesas Islands; live in 600-708 m.

DESCRIPTION. — Shell up to c. 13 mm in height, fragile, opaque to semi-transparent, flattened, left valve slightly more convex than right valve, nearly circular, slightly wider than high, inequivalve, sculpture of left valve somewhat reticulated, right valve commarginally sculptured, equilateral, auricles unequal in shape and size (anterior larger than posterior).

Left valve sculptured with delicate commarginal lamellae (somewhat curled ventrally), commencing at c. 2 mm from umbonal margin, widely spaced (c. 0.8 mm apart), extending to the ventral margin, closely spaced (c. 0.1 mm apart)

FIGS 11-19. 11-17, Parvamussium lozoueti n. sp., holotype MNHN 20449,H 17.0 mm, L 17.9 mm, BORDAU 1 stn CP 1415; 11, left valve, exterior; 12, right valve, exterior; 13, paratype MNHN 20450, BORDAU 1 stn CP 1415, left valve, interior, H 14.5 mm, L 16.2 mm; 14, paratype MNHN 20452, BORDAU 1 stn DW 1485, right valve, interior, H 12.7 mm, L 12.6 mm; 15, right valve, microsculpture, scale bar 1 mm; 16, right valve, microsculpture, scale bar 300 Μm; 17, left valve, microsculpture, scale bar 2 mm. 18-19, Parvamussium dautzenbergi (Dijkstra, 1990) , SALOMON 1 stn DW 1741; 18, left valve, exterior; 19, left valve, interior, H 8.1 mm, L 7.7 mm.

and prominently sculptured near the margin. Lamellae overrun irregularly spaced, delicate radial lirae (c. 8 per mm over central part of disc). Anterior auricle with wider set, more prominent commarginal lamellae than posterior.

Right valve with closely spaced, regularly arranged commarginal lirae, weak in early growth stage, more lamellated near ventral margin. Marginal apron (c. 1 mm wide) pressed to left valve. Auricles with closely spaced, prominent commarginal lamellae. Hinge line straight. Byssal notch moderately deep and small, byssal fasciole narrow. Internally 11 radial ribs, commencing 3 mm from umbonal margin, extending to marginal apron.

Dimensions of holotype: H 12.8, W 12.9, D 3.3.

REMARKS. — Parvamussium multiliratum Dijkstra, 1995 is a somewhat similar bathyal species, known from New Caledonia ( Dijkstra 1995: 26), Wallis and Futuna and Vanuatu ( Dijkstra 2001: 83). The two species are similar in shape (circular) and in the lamellar sculpture of the left valve, but can be differentiated by the following characters:

P. marquesanum

Height c. 13 mm

Sculpture lv reticulate

Internal ribs 11 (coarse) P. multiliratum

c. 9 mm

commarginal lamellae

14+ (delicate)

Parvamussium retiaculum Dijkstra, 1995 , known from similar localities to P. multiliratum and from the Norfolk Ridge and Kermadec Islands (Dijkstra & Marshall 1997: 81), has somewhat similar internal ribs and reticulate sculpture on the left valve but differs from P. marquesanum in having an elongate shape (higher than wide), a smaller size (up to c. 7 mm in height) and a larger anterior auricle with more prominent sculpture.

ETYMOLOGY. — After the Marquesas Islands. Parvamussium multiliratum Dijkstra, 1995

Parvamussium multiliratum Dijkstra, 1995: 26 , figs 31-34, 91-92.

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10: stn CP 1332, 16˚56’S, 178˚078’E, 640-687 m, 1 spm. Tonga. BORDAU 2: stn DW 1543, 21˚16’S, 175˚18’W, 427-436 m, 1 rv; stn DW 1630, 23˚23’S, 176˚18’W, 360 m, 1 rv.

DISTRIBUTION. — New Caledonia, Wallis and Futuna, and Vanuatu ( Dijkstra 2001: 83); live in 748-2110 m. New records for Fiji and Tonga. Present material live in 640-687 m.

REMARKS. — The juvenile specimen from Fiji is smooth, without commarginal sculpture.