Palliolum minutulum Dijkstra & Southgate, 2000
DIJKSTRA, H. H. & P. C. SOUTHGATE. 2000. A new living scallop (Bivalvia: Pectinidae) from the southwestern Pacific. Molluscan Research, 20 (2): 13-18, figs. 1-7. [p. 14, figs. 1-7]
2000 Palliolum minutulum Dijkstra & Southgate, 2000
H. H. Dijkstra & P. C. Southgate, 2000, figures 1-7.
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«Description: Shell small, orbicular, equiconvex, equilateral, translucent, up to ca. 9 mm high, auricles nearly equal in size, umbonal angle about 90°. Prodissoconch ca. 110 μm in height. Left valve smooth, glossy, with minuscule antimarginal scratches and commarginal lirae near anterior margins of auricle and disc. Microscopic sculpture lacking near posterior and ventral margins. Anterior and posterior auricles gradually transitionally developed into disc without demarcating disc flanks. Hinge line nearly straight, antero-dorsal margin slightly raised. Auricular crura without dorsal and intermediate teeth. Resilifer wide triangular. Right valve with similar microsculpture to that of left valve. Anterior auricle prominent, somewhat curved, with four irregularly arranged radial riblets bearing fine gemmae where they are crossed by the fine commarginallirae. Byssal fasciole rather broad; byssal notch weakly indented; ctenolium well developed on suture, functional segment with 10 small teeth (active ctenolium). Exterior translucent cream, with white tent-shaped maculations; soft parts dark brown.
Dimensions of the holotype: Height 6.8 mm, Length 6.6 mm, Depth (diameter) 1.0 mm. Type material: Holotype (db) MNHN and 6 paratypes (db) (MNHN, 5 db; HD 6691, 1 db). Type locality: New Caledonia, coral reef lagoon off Koumac, between mainland and Infernet reef, 20°34.4'5, 164°13.0'E, 12-14 m, bottom of flat slabs with gorgonians and ooze, live, Montrouzier stn 1299, Oct. 1993. Other material examined: New Caledonia. MNHN, 3 lv, 2 rv, HD 6692 (1 lv, 1 rv), NW New Caledonia, 20°34'S, 164°16'E, 0-2 m, dead, Montrouzier stn 1277, act. 1993; MNHN, 2 lv, NW New Caledonia, 20°34.5'S, 164°15.5'E, 3-7 m, dead, Montrouzier stn 1297, Oct. 1993; MNHN, 1 lv, NW New Caledonia, 20°35.8'S, 164°12.7'E, 9-10 m, dead, Montrouzier stn 1302, Oct. 1993; MNHN, 1 rv, NW New Caledonia, 20°40'S, 164°11.2'E, 12 m, dead, Montrouzier stn 1316, Oct. 1993. Australia. AMS C.165165, 2 rv, Queensland, Lizard Island, Granite Bluff, in 23 m, sandy mud bottom, many forams, some green mixed algae & Caulerpa spp., leg. W.F, Ponder, 7 Dec. 1974;AM5 C.165166, 1 rv, Queensland, Lizard Island, off East Face, ca. 20 m, foraminiferous, leg. W.E Ponder, P.H. Colman, I. Loch, 11 Dec. 1974; AM5 C.165167, 1 rv, Queensland, Endeavour Reef, 14°57'S, 145°35'E, 8-10 m, rubble wash on outer reef slope, leg. I. Loch, 9 Dec. 1984; HD 6733, 11 db, 7 lv, N Queensland, Pioneer Bay, Orpheus Island, 18°35'S, 146°29'E, from submerged nets, live, 6 m, leg. P. Southgate. Solomon Islands. AMS C.165168, 2 lv, 2 rv, W Malaita Island, Aoki Harbour, on sheltered side of reef on slopes, 3-7.5 m, coral & rubble bottom, brown algae washings, leg. P.B. Colman, 18 Aug. 1973; NMNZ MF,30460, 8 lv, 6 rv, Vangunu Island, Marovo Lagoon, between Telina Island and Mbareki Peninsula, amongst shell grit & rubble, 9 m, 6 Oct. 1965; NMNZ MF.59756 and NMNZ MF.59756, 4 lv, 4 rv, Vangunu Island, Marovo Lagoon, off Telina Island, amongst shell grit & rubble, 11 m, 26 Oct. 1965; PS P.1314, 4 db, Nusa Tupe Island, Gizo, attached to submerged nets, live, 6-10 m, leg. K. Friedman. Fiji. PS P.1315, 1 db, off Savusavu on the island of Vanua Levu, 16°34'S, 179°15'E, attached to submerged nets, live, 8-10 m, leg. P. Southgate. Kiribati. PS P.1332, 7 db, lagoon of Abaiang atoll, off Taburao, 0°59'N, 172°59'E, attached to submerged nets, live, 6-8 m, leg. A. Beer. Distribution: Solomon Islands, northern Queensland (Australia), New Caledonia, Fiji and Kiribati, 0-14 m, living in 6-14 m amongst algae on soft sediments. Discussion Palliolum minutulum is closest in outline to Palliolum incomparabile (Risso, 1826), known from the Mediterranean Sea and the adjacent area of the eastern Atlantic. Both species are almost circular in shape, fragile, usually transparent and highly coloured. However, P. incomparabile is larger (up to ca. 13 mm high) with prominent antimarginal microsculpture; P. minutulum is smaller (up to ca. 10 mm high, usually smaller to 8 mm) with minuscule antimarginal scratches or smooth. Remarks The present species is live collected amongst algae in shallow water. The size attained by live specimens held under culture conditions for up to 8 months was 6-8 mm in height. The largest specimen examined, from Gizo in the Solomon Islands, was 9.2 mm in height. Etymology The species is named after its small dimension (Latin minutulus, adj. = very small).» HENK H. DIJKSTRA & PAUL C. SOUTHGATE, 2000
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«Type data. — Holotype (H 6.8 mm, pv) MNHN Moll 21160, 6 paratypes (pv), 5 MNHN Moll 21161, 1 ZMA Moll. 400011. Type locality: New Caledonia, coral reef lagoon off Koumac, between mainland and Infernet reef, 20˚34.4’S, 164˚13.0’E, 12-14 m, alive, bottom of flat slabs with gorgonians and ooze, x.1993 (Montrouzier stn 1299).
Description. — Shell extremely fragile, up to c. 9 mm high, translucent, circular, almost equiconvex and equilateral, auricles almost equal in size, umbonal angle about 90˚; base colour highly variable, translucent white, cream, pink, reddish, or brownish, with white tent-shaped maculations. Both valves smooth and glossy, with minute antimarginal scratches and commarginal growth lines. Auricles of left valve gradually merging into disc without demarcating disc flanks. Anterior auricle of right valve demarcated from disc flank, prominent, somewhat curved, with four unevenly spaced radial riblets bearing delicate gemmae where crossed by fine commarginal lirae. Posterior auricle of right valve not demarcated from disc flank. Hinge line almost straight, antero-dorsal margin slightly raised. Resilifer widely triangular. Byssal notch shallow, byssal fasciole rather broad, functional ctenolium well-developed with c. 10 small teeth. Hinge teeth lacking. Distribution. — Solomon Islands, northern Queensland, New Caledonia, Fiji and Kiribati: 6-16 m (Dijkstra & Southgate, 2000: 16), Indonesia: littoral depth (Dijkstra & Moolenbeek, 2008: 22); Philippines: 50-100 m (Raines, 2010: 594). Present specimens from the Philippines alive at 4-28 m (minimum depth range). The bathymetric range of live-taken specimens is 2-100 m. Living generally amongst algae on substrata. Remarks. — Specimens from the Philippines are identical to the type material from New Caledonia. This tiny small alga-dwelling species strongly vary in colour.» DIJKSTRA, H. H. 2013. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica, 10: 1-108, pls. 1-32. [p. 26, 27]
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Palliolum minutulum Dijkstra & Southgate, 2000; H. H. Dijkstra, 2013, Pectinoidea from the Panglao region, Philippine Islands, plate 5, figures 3a-3d
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