Parvamussium cancellorum Dijkstra & Marshall, 2008
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. 6, figs. 4A-4G, 5]
2008 Parvamussium cancellorum Dijkstra & Marshall, 2008
H. H. Dijkstra & B. A. Marshall, 2008, figure 4.
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«Type material
Holotype NMNZ M.173000 (lv) and many paratypes (2 each AMS C.205270, MNHN, ZMA Moll. 4.07.001, rest NMNZ M.172907), southern Norfolk Ridge, NW of Cape Reinga, northern New Zealand, 33°22.61’S, 170°12.70’E, 514–540 m, 1 Jun. 2003, RV Tangaroa. Material examined
The type material (see above). West Norfolk Ridge, Wanganella Bank, 32º10.5’S, 167º21.2’E, 442–449 m (7 v, M.174027). Norfolk Ridge, N of Norfolk Island, 26°25.94’S, 167°10.87’E, 750–774 m (20 v, M.172013). Description
Shell up to 7 mm high, subcircular, equivalve (broad, thin ventral margin of right valve disintegrating post mortem), almost equilateral, left valve distinctly more convex than right valve, auricles dissimilar in shape, anterior auricle considerably larger than posterior one, umbonal angle c. 100º, resilifer triangular, internal ribs present 12–13 on left valve and 11 on right valve. Translucent white, typically with a few scattered, irregular opaque white and yellowish brown maculations. Prodissoconch c. 170 μm long, D-shaped, smooth, convex, rim flanged. Dissoconch left valve disc and auricles markedly shiny up to 800–900 μm height, smooth apart from commarginal growth lines. Subsequent disc and auricles matt due to dense microsculpture of minute pits. Disc sculptured with crisp commarginal lamellae numbering 5–10 per mm, typically 9 or 10 per mm over most of disc, closer and more numerous near adult ventral margin, few specimens commencing with c. 5 lamellae per mm, increasing to 10 or more at maturity. Low, close radial riblets finely crenulated where intersecting commarginal ribs, on anterior and posterior quarters throughout, gradually resolving near ventral margin in adults. Auricular sculpture similar to that of disc, though commarginal lamellae closer, especially posteriorly; some specimens additionally with fine, crowded riblets in ‘camptonectes’ pattern on posterior part of anterior auricle. Right valve disc sculptured with crisp, rather regularly spaced commarginal ridges interspaces matt. Posterior auricle continuous with disc, sculptured with closely spaced commarginal lamellae and finer radial threads and granules; anterior auricle and byssal fasciole separated from disc by sharply incised groove, sculptured with commarginal lamellae, and 5–7 subequal radial threads on ventral half. Byssal notch shallow. Distribution
Norfolk Ridge and West Norfolk Ridge, 442–774 m (shells only) (Fig. 5). Remarks
Parvamussium cancellorum is superficially closely similar to Pa. retiolum Dijkstra, 1995, from New Caledonia, Wallis and Futuna, and Vanuatu (Dijkstra 2001: 86), but is separable by the glossy early dissoconch, which is essentially smooth until the shell is 800–900 μm high, instead of matt due to the presence of densely crowded minute threadlets and granules in Pa. retiolum. Pa. cancellorum differs further from Pa. retiolum in attaining smaller size (height up to 7 mm, versus 16 mm), in having finer and one or two extra internal ribs on each valve, in having finer and closer commarginal ribs on the right valve, and in the left valve having considerably weaker radial sculpture, and more crowded commarginal sculpture. The two species are locally sympatric (see below). Etymology
Lattice-work (Latin), alluding to the sculpture of the left valve.» HENK H. DIJKSTRA & BRUCE A. MARSHALL, 2008
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«Habitat. Collected in the bathyal zone, free on soft sediment (so far empty shells only).
Distribution. West Norfolk Ridge and Norfolk Ridge, 442–774 m (Dijkstra & Marshall, 2008: 7). Present specimens from Australia (Middleton Reef, New South Wales) dead at 295–298 m.
Remarks. The present specimens from Middleton Reef have more delicate and somewhat more closely spaced commarginal sculpture on the left valve than the type specimens from the Norfolk Ridge, but other characters are similar.
Parvamussium cancellorum 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. 133]
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Parvamussium cancellorum Dijkstra & Marshall; H. H. Dijkstra & A. G. Beu, 2018, Living scallops of australia and adjacent waters, figures 6E, 6G-6J.
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