Parvamussium squalidulum 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. 32, figs. 47-50]
1995 Parvamussium squalidulum Dijkstra, 1995
H. H. Dijkstra, 1995, figures 47-54.
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«TYPE MATERIAL. — Holotype MNHN. Paratypes: 2 AMS C201714, 3 HD, 6 MNHN, 2 USNM.
TYPE LOCALITY. — Lord Howe Rise, Kelso Bank, MUSORSTOM 5, stn DW 277, 24°11' S, 159°35' E, 270 m.
MATERIAL EXAMINED. — Chesterfield Islands. MUSORSTOM 5: stn DW 255, 25°15' S, 159°55' E, 280-295 m, 1 lv, 2 rv. - Stn DW 258, 25° 33' S, 159°46' E, 300 m, 7 Iv, 3 rv. — Stn DW 260, 25°29' S, 159°44' E, 285 m, 1 Iv. — Stn DW 261, 25°27' S, 159°46' E, 300 m, 2 rv. — Stn CP 268, 24°45' S, 159°39' E, 280 m, 41v. — Stn CP 269, 24°47' S, 159°37' E, 250-270 m, 1 Iv. — Stn DW 272,24°41' S, 159°43' E, 500-540 m, 1 Iv, 3 rv. — Stn DW 274, 24°45' S, 159°41' E, 285 m, 1 Iv. — Stn DW 277, 24°11' S, 159°35' E, 270 m, 4 spms, 2 lv, 8 rv (holotype and paratypes: 2 AMS, 3 HD, 6 MNHN, 2 USNM). — Stn CP 279, 24°09' S, 159°38' E, 260-270 m, 6 lv, 1 rv. — Stn DW 299, 24°48' S, 159° 24' E, 360-390 m, 2 lv, 3 rv. — Stn DW 301, 22°07' S, 159°25' E, 487-610 m, 1 Iv.
Loyalty Islands. MUSORSTOM 6: stn DW 480,21°08' S, 167°56' E, 380 m, 1 lv, 1 rv. New Hebrides Arc ¹. VOLSMAR: stn DW 7, 22°26' S, 171°44' E, 325-400 m, 1 spm, 1 Iv. — Stn DW 17,22°23' S, 171°41' E, 260-300 m, 1 Iv. DISTRIBUTION. — Chesterfield Islands, New Caledonia to the New Hebrides Arc; shells in 260-610 m, alive in 260-400 m.
DESCRIPTION. — Shell rather small, suborbicular, inequivalve, inequilateral, semi-transparent, up to ca. 11 mm high, left valve slightly more convex than right; auricles rather small, unequal; umbonal angle about 125°.
Prodissoconch ca. 210 μm in height. Left valve with numerous irregularly spaced, scaly radial costae, a few commencing weakly at about 1 mm shell height, increasing in number towards the ventral margin; small delicate concentric lamellae developing between them, more closely spaced near ventral margin. Anterior auricle well developed, posterior rather small. Three very weak radial lirae on anterior auricle, absent on posterior. Both auricles covered with concentric lamellae. Hinge line straight. Right valve with minute concentric lirae near the lateral margin, absent from central region of disc. Marginal apron (outer prismatic calcite layer) mostly broken off, covered with fine concentric lirae (marginal region below the internal lirae). Anterior auricle well developed, provided with 5 radial riblets that are covered with con-centric lamellae, stronger on dorsal margin. Posterior auricle with delicate lamellae. Ten irregularly spaced internal lirae, plus 2 rudimentary lirae. One auricular lira on posterior auricle, absent on anterior. External sculpture and coloration slightly visible internally. Resilifer triangular. Byssal notch present, no ctenolium. Left valve creamy, with white and orange-brown maculations, right valve semi-transparent white and glossy. Dimensions of the holotype: H 11.1, L 11.4, D 2 mm. REMARKS. — The closest species is Parvamussium sinense, the left valve of which is more strongly sculptured with closely spaced scaly radial costae than in P. squalidulum. The latter is slightly more orbicular, and the right valve is covered with delicate concentric lirae, which are absent in P. sinense. The internal lirae of P. sinense are more regularly spaced with more stronger developed terminal nodules at the distal ends. Another related species is P. scitulum, the left valve of which is more delicately sculptured with close-set radial striae (sometimes absent), while concentric lirae are also absent on the right valve. P. squalidulum is slightly more convex than P. scitulum.»
ETYMOLOGY. — From numerous scaly radial costae of the exterior of the left valve (Latin squalidulus, adj. = with small scales).»
¹Although the condominium of the New Hebrides has become independant under the name of Vanuatu, the term New Hebrides is retained here to designate the Hunter and Matthew area of the New Hebrides Arc. Hunter and Matthew are a dependency of New Caledonia. Similarly, geographers and geophysicists have retained the expression New Hebrides Trench.
HENK H. DIJKSTRA, 1995
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