Parvamussium maorium Dell, 1956
DELL, R. K. 1956. The archibenthal Mollusca of New Zealand. Dominion Museum Bulletin, 18: 1-235, pls. 1-25, text-figs. 1-6. [p. 20, pl. 4, figs. 30, 31]
1956 Parvamussium maorium Dell, 1956
R. K. Dell, 1956, plate 4.
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«Shell attaining a large size for the group, disc practically equilateral, little inflated, both valves sculptured internally with 9 raised lamellae. Right valve (holotype) with an anterior ear much smaller than posterior, posterior ear indented by moderately deep byssal sinus, free margins of ear extended by a transparent thin shell layer, the edges exceedingly fine with roughened edges, easily broken back to the thickened portion of the ear which has a smooth, almost straight margin. Disc strongly marked off from ears, sculptured with fine, regular, concentric incised grooves, with fine, short, interstitial radials, most strongly developed near the margins, the internal lamellae showing through. Interior polished, with 9 ribs which gradually develop below the beaks and continue ahnost to the margin in subadult shells, a layer of white callus over the upper half of disc. In fully adult shells the internal ribs stop at a greater distance from edge of valve (up to one-third of diameter). Margins of valve smooth. Left valve with subequal beaks, outer surface of valve apparently smooth but with sparse, irregular microscopic radial scratches. The internal lamellae show through more distinctly in this valve.
Length, 10.5 mm.; height, 12.0 mm.; inflation, 1.0 mm. (holotype, right valve); length, 13.6 mm.; height, 14.6 mm.; inflation, 1.8 mm (paratype, left valve). Holotype (M.9171) and paratypes in Dominion Museum. Paratypes also in Canterbury Museum. Localities: Portobello Alert Station 54-17, off East Otago coast, in 260-350 fathoms (type); C.I.E. Station 41, south-east of Pitt Island, in 330 fathoms. There is some variation in the material available in the development of sculpture, especially in the relative length of the internal ribs, though these latter are constant in number. The sculpture, although different in the two valves is not highly discrepant and the species seems best classed in Parvamussium. This is the first living representative of this genus from New Zealand waters although it does occur in the Tertiary.» RICHARD KENNETH DELL, 1956
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«Description. Shell up to c. 14 mm high, fragile, translucent to almost opaque, inequivalve, equilateral (juvenile), inequilateral (adult), higher than wide, left valve slightly more convex than right valve, auricles unequal in size, umbonal angle c. 90°. Whitish with fine dull white maculations on left valve.
Left valve acline to weakly posteriorly elongate (prosocline), weakly sculptured laterally with unevenly and closely spaced radial riblets, more prominent posteriorly. Central part of disc smooth. Antero-ventrally also with delicate, closely spaced commarginal lamellae. Anterior auricle with commarginal lamellae near disc flank and more dorsally with a few delicate antimarginal riblets, posterior auricle with a few weak antimarginal riblets. Dorsal margin straight. Right valve sculptured with evenly spaced commarginal lamellae. Auricles somewhat raised dorsally, due to commarginal sculpture. Anterior auricle weakly commarginally sculptured, dorsally more prominent, with one antimarginal riblet near pseudo-fasciole, posterior auricle almost smooth. Byssal notch relatively deep. Interior of both valves with 10–11 radial riblets, most specimens with 10 riblets, somewhat curved in posterior direction; with a small auricular riblet laterally. Habitat. Living in the bathyal and abyssal zones, free on soft sediment (muddy sand or mud).
Distribution. New Zealand and Chatham Islands: many lots from throughout the New Zealand EEZ, from Three Kings Rise (31°30.7'S 172°49.8'E, 1216–1385 m; 1 v, NIWA U602) to off Campbell Island (53°29'S 169°48'E, 589–594 m; 1 v NMNZ M.39553), as shallow as 168 m in the Southland fiords, but in 349–1208 m elsewhere (Dijkstra & Marshall, 2008: 9, fig. 7). Now also Tasman Sea and southeastern Australia (New South Wales, Victoria and Tasmania). The live-taken specimen from the Tasman Sea is the only record from an abyssal depth (2450 m). Present specimens from Australia dead at 183–1000 m, alive at 400–720 m.
Remarks. The present specimens from south-eastern Australia are morphologically identical to the type specimens from New Zealand.
Parvamussium maorium is a new record for Australia.» DIJKSTRA, H. H. & A. G. BEU. 2018. Living scallops of Australia and adjacent waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae). Records of the Australian Museum, 70 (2): 113-330, figs. 1-102. [p. 135]
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Parvamussium maorium Dell, 1956; H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 8A, 8B, 8H, 8I, 8L.
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«Description
Supplementary to that of Dell (1956). Prodissoconch c. 170 μm long, smooth, D-shaped, convex, rim narrowly flanged, sharply separated from dissoconch. Early dissoconch of both valves with microsculpture of fine, crisp, irregularly wavy diverging and converging radial threads. Distribution
Southern Lord Howe Rise and New Zealand, 168–1385 m, taken alive at 168–1208 m. Lives as shallow as 168 m in Fiordland where unusual hydrographic conditions prevail (Grange et al. 1980), but unknown living elsewhere shallower than 349 m (typically >500 m) (Fig. 7). Remarks
Parvamussium maorium ranges from almost circular in shape to markedly posteriorly oblique, and the shell may be orange, orange-spotted, white, opaque or translucent. Unlike the glossy right valve, the left valve has a slight but distinctly matt texture, and may be essentially smooth, or (typical of East Otago), sculptured from mid to late ontogeny with radial threads that gradually enlarge to varying degrees, with or without the addition of commarginal lamellae. As already indicated, specimens of Pr. investigatoris have been misidentified as Propeamussium maorium (Dell 1963b; Dijkstra and Marshall 1997). Propeamussium investigatoris, which is locally sympatric (asyntopic), with Pa. maorium off the northern North Island has much stronger radial sculpture on the left valve, and far more conspicuous sculpture on the anterior and posterior ends of the right valve, on which, additionally, the internal radial ribs are considerably broader.» DIJKSTRA, H. H. & B. A. MARSHALL. 2008. The recent Pectinoidea of the New Zealand region (Mollusca: Bivalvia: Propeamusiidae,Pectinidae and Spondylidae). Molluscan Research, 28 (1): 1-88, figs. 1-70. [p. 9, 10]
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Parvamussium maorium Dell, 1956; H. H. Dijkstra & B. A. Marshall, 2008, The recent Pectinoidea of the New Zealand region, figures 6E-6I.
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