Parvamussium retiolum Dijkstra, 1995
DIJKSTRA, H. H. 1995. Bathyal Pectinoidea (Bivalvia: Propeamussiidae, Entoliidae, Pectinidae) from New Caledonia and adjacent areas. In Bouchet, P. (Ed.), Résultats des Campagnes MUSORSTOM, Volume 14. Mémoires du Muséum national d'Histoire naturelle, 167: 9-73, figs. 1-154. [p. 29, figs 39-42, 97]
1995 Parvamussium retiolum Dijkstra, 1995
H. H. Dijkstra, 1995, figures 39-46, 93-98.
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«TYPE MATERIAL. — Holotype MNHN. Paratypes: 36 MNHN, 2 AMS C201713, 2 HD, 2 NMNZ M268537, 2 NSMT, 2 USNM.
TYPE LOCALITY. — Chesterfield Islands, MUSORSTOM 5, stn CP 363, 19°47' S, 158°44' E, 685-700 m.
MATERIAL EXAMINED. — Chesterfield Islands. MUSORSTOM 5: stn DW 340, 19°48' S, 158°40' E, 675-680 m, 1 spm, 1 lv, 3 rv. — Stn DW 341, 19°45' S, 158°43' E, 620-630 m, 5 spms, 3 lv, 3 rv. Stn DC 357, 19°37' S, 158°45' E, 630 m, 2 lv, 2 rv. — Stn DC 358, 19°38' S, 158°47' E, 680-700 m, 4 spms, 1 lv, 5 rv. — Stn CP 363, 19°47' S, 158°44' E, 685-700 m, 41 spms, 6 Iv (holotype and paratypes). — Stn CP 364, 19°45' S, 158°46' E, 675 m, 1 spm. - Stn DC 380, 19°37' S, 158°43' E, 555-570 m, 1 Iv.
New Caledonia. BIOCAL: stn DW 56, 23°34' S, 167°11' E, 695-705 m, 1 lv, 7 rv. MUSORSTOM 4: stn CP 158, 18°49' S, 163°15' E, 620 m, 1 Iv. - Stn DC 168, 18°48' S, 163°10' E, 720 m, I spm. DISTRIBUTION. — New Caledonia and Chesterfield Islands, 555-720 m, living 620-720 m.
DESCRIPTION. — Shell rather small, inequivalve, inequilateral, up to ca. 16 mm high, left valve somewhat more convex than right, translucent white, auricles unequal, umbonal angle about 95°
Prodissoconch ca. 220 μm in height. Left valve covered with delicate concentric lamellae crossing closely spaced radial riblets, somewhat coarser near umbonal area, finer near ventral margin. Anterior auricle well developed, with many fine radial riblets that are crossed near margin by fine concentric lamellae; posterior auricle similary sculptured. Hinge line straight. Right valve with regular concentric lirae, closely spaced near umbonal area, becoming more widely spaced towards the ventral margin. Microscopic interstitial radial scratches near margins. Auricles strongly developed, with concentric lamellae that are more prominent anteriorly. Strongly developed scales on antero-dorsal margin. Internal lirae 10, plus 1 posterior auricular lira and 4 rudimentary auricular lirae on left valve and 3 on right, ends nodose. ligament near resilifer. Byssal notch small, no ctenolium. Resilifer triangular, elongate. Strongly developed outer Dimensions of the holotype: H 16, L 14.8, D 3.5 mm. REMARKS. — Parvamussium retiolum is somewhat similar to P. thetidis, which also occurs in the study area (see below). P. retiolum is larger, with a fine cancellate sculpture on left valve; the latter species has irregularly spaced, strong radial costae crossed by delicate concentric lamellae. Auricles and right valve of P. retiolum more sculptured with closely spaced, concentric lamellae. Internallirae variable, somewhat similar to P. thetidis.
Parvamussium retiolum differs from P. retiaculum in its more delicate cancellate sculpture on left valve, and in having more closely spaced, concentric lamellae on right valve. Internal lirae of P. retiolum start earlier. In all aspects P. retiolum is representative of Parvamussium. ETYMOLOGY. — From the cancellate sculpture of the left valve (Latin retiolum, n. = small net).»
HENK H. DIJKSTRA, 1995
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