Parvamussium polynesianum, 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 : 92-94

Parvamussium polynesianum n. sp.

Figs 26-31

TYPE MATERIAL. — Holotype (spm) MNHN 20459 and 19 paratypes MNHN 20460 , 3 HD.

TYPE LOCALITY. — Marquesas Islands, Hiva Oa , 09˚49’S, 140˚00’W, 210-258 m [MUSORSTOM 9: stn DR 1199] .

MATERIAL EXAMINED. — Marquesas. MUSORSTOM 9: stn DW 408 m, 5 rv; stn DR 1253, 09˚48’S, 139˚38’W, 360-405 m, 1 rv; 1146, 09˚19’S, 140˚06’W, 200 m, 3 lv, 1 rv; stn DR 1198, 09˚50’S, stn DR 1255, 09˚38’S, 139˚48’W, 416-440 m, 1 lv; stn DW 1287, 139˚09’W, 290-320 m, 4 rv, 1 lv; stn DR 1199, 09˚49’S, 140˚00’W, 07˚54’S, 140˚40’W, 163-245 m, 19 rv, 2 lv (19 paratypes MNHN 210-258 m, 2 spm (holotype MNHN 20459 and paratype HD); 20460, 2 HD); stn DW 1288, 08˚54’S, 139˚38’W, 200-220 m, 2 stn DW 1201, 09˚51’S, 139˚09’W, 275-300 m, 4 rv, 2 lv; stn DW rv; stn DR 1298, 08˚49’S, 140˚17’W, 305 m, 3 rv, 2 lv; stn DR 1206, 09˚51’S, 139˚09’W, 352-358m, 2 rv; stn DW 1222, 09˚44’S, 1299, 08˚49’S, 140˚17’W, 405-418 m, 1 rv .

138˚51’W, 252-340 m, 2 rv; stn DR 1231, 09˚42’S, 139˚05’W,

270-285 m, 1 spm, 2 lv; stn DW 1234, 09˚42’S, 139˚06’W,

DISTRIBUTION. — Marquesas Islands; shells in 200-416 m, live in 258-270 m.

DESCRIPTION. — Shell up to c. 5.5 mm in height, fragile, opaque to semi-transparent, left valve slightly more convex than right valve, nearly circular, somewhat higher than wide, inequivalve, sculpture of left valve somewhat reticulate, right valve commarginally sculptured, equilateral, auricles unequal in shape and size (anterior larger than posterior).

Left valve sculptured with delicate commarginal lamellae, commencing at c. 1 mm from umbonal margin, closely spaced (c. 0.1 mm apart on central part of disc), extending to ventral margin. These thin and somewhat undulated lamellae overrun widely and irregularly spaced, radial lirae (on central part of disc c. 5 per mm), increasing in number to ventral margin. Anterior auricle more prominently sculptured than posterior with coarse, ventrally curled commarginal lamellae, posterior auricle sculpture more delicate and more closely spaced.

Right valve with closely spaced, regularly arranged weak commarginal lirae. Marginal apron (c. 0.8 mm high) pressed to left valve, broken off many specimens. Anterior auricle with coarse commarginal lamellae, posterior more delicate. Hinge line straight. Byssal notch shallow, byssal fasciole narrow. Internally 10 prominent radial ribs, with a weak auricular rib on each side, commencing 2 mm from umbonal margin, extending nearly to ventral margin.

Dimensions of holotype: H 5.3, W 5.2, D 1.5.

REMARKS. — The delicate and somewhat undulated commarginal lamellae on the left valve of the present species resemble the sculpture of Parvamussium undisonum Dijkstra, 1995 , known from New Caledonia, Loyalty Islands, Vanuatu ( Dijkstra 1995: 37) and Wallis and Futuna ( Dijkstra 2001: 87), but other characters differ strongly:

P. polynesianum

Height up to 5.5 mm

Shape nearly circular

Sculpture lv delicate

Internal ribs 10 P. undisonum

up to c. 14 mm

oblong and oblique

coarse

10 + rudimentary

The sculpture of the left valve of P. polynesianum also somewhat resembles that of Parvamussium thetidis (Hedley, 1902) , known from eastern Australia as far east as Tonga. Parvamussium polynesianum differs in having a more circular shape (more oblong and oblique in P. thetidis ), more delicate sculpture (coarser in P. thetidis ) and more radial lirae (more prominent and fewer in number in P. thetidis ). The two species also have similar internal ribs, although P. thetidis often has additional rudimentary ones, which are lacking in P. polynesianum .

ETYMOLOGY. — After Polynesia. Parvamussium retiaculum Dijkstra, 1995

Parvamussium retiaculum Dijkstra, 1995: 28 , figs 35-38.

MATERIAL EXAMINED. — Norfolk Ridge. NORFOLK 1: stn spm, 1 lv, 4 rv . — BORDAU 1: stn DW 1485, 19˚03’S, 178˚30’W, DW 1697, 24°39’S, 168°38’E, 569-616 m, 6 lv, 2 rv. 700-707 m, 2 lv.

Fiji. MUSORSTOM 10: stn CP 1331, 17˚02’S, 178˚02’E, 694-703 Tonga. BORDAU 2: stn DW 1508, 21˚02’S, 175˚19’W, 555- m, 1 spm, 1 lv, 1 rv; stn CC 1336, 16˚58’S, 177˚58’E, 797-799 581 m, 1 lv, 1 rv; stn DW 1544, 21˚18’S, 175˚18’W, 441-443 m, m, 1 spm, 1 rv; stn CP 1341, 16˚53’S, 177˚44’E, 500-614 m, 1 1 rv; stn CP 1640, 21˚09’S, 175˚24’W, 564-569 m, 2 spms.

DISTRIBUTION. — Southern New Caledonia, southeast of Norfolk Island and Kermadec Islands ( Dijkstra 2001: 85); live in 540-700 m. New records for the Norfolk Ridge, Fiji and Tonga. Present material live in 569-797 m.

Parvamussium retiolum Dijkstra, 1995

Parvamussium retiolum Dijkstra, 1995: 29 , figs 39-42, 97.

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10: stn CP 1330, 310- 420 m, 1 spm.

17˚10’S, 177˚56’E, 567-699 m, 2 spms. — BORDAU 1: stn CP Tonga. BORDAU 2: stn DW 1509, 21˚05’S, 175˚22’W, 456-510 1396, 16˚39’S, 179˚57’W, 591-596 m, 1 spm; stn CP 1413, m, 4 lv, 3 rv; stn DW 1537, 21˚41’S, 175˚19’W, 391-421 m, 11 16˚10’S, 179˚24’W, 669-676 m, 2 lv; stn DW 1432, 17˚20’S, lv, 25 rv.

178˚44’W, 477-493 m, 1 lv; stn CP 1476, 19˚41’S, 178˚11’W,

DISTRIBUTION. — New Caledonia, Wallis and Futuna and Vanuatu ( Dijkstra 2001: 85); live in 552-750 m. New records for Fiji and Tonga. Present material live in 420-591 m.