Hyalopecten hadalis (Knudsen, 1970)
KNUDSEN, J. 1970. The systematics and biology of abyssal and hadal Bivalvia. Galathea Report, 11: 1-241. [p. 98, pl. 13, fig. 2, text-figs 61, 62]
1970 Cyclopecten (Hyalopecten) hadalis Knudsen, 1970
J. Knudsen, 1970, plate 13.
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«Material:
St. 650, Kermadec Trench (32° 20' S, 176° 54' W), 6620-6730 m, 15 Feb. 1952. Gear: ST 600. Bottom: brown clay with pumice. Bottom temp.: (1.3° C). - 1 specimen. St. 651, Kermadec Trench (32° 10' S, 177° 14' W), 6960-7000 m, 16 Feb. 1952. Gear: HOT. Bottom: brown clay with pumice. Bottom temp.: (1.3°C). - 1 juvenile specimen. Diagnosis: A Cyclopecten in which the right anterior auricle is separated by a distinct groove with distinct pectinidial teeth, and with a rather convex left valve and a less convex right valve. The ventral part of the membranous velum is broad and the mantle edge has shorter tentacles interspaced between very long ones, the latter reaching the edge of the velum. The foot is small, the byssus consisting of numerous threads. Left and right retractors present, the former twice the thickness of the latter. Fig. 61. Cyclopecten hadalis n.sp. A, type, "Galathea" St. 650, exterior of left valve; B, paratype, "Galathea" St. 651, exterior of left valve. PHW.
Description:
The valves are extremely delicate and hyaline, slightly higher than long. It is equilateral and strongly inequivalve, the left valve being considerably more convex than the right one. The dorsal edge is straight. The valves are rather smooth at the umbo, where only a fine irregular concentric striation is present. In addition both valves have a fine radiating sculpture and are provided with sharp regular and prominent ribs which gradually develop into rounded undulations towards the periphery. This is particularly the case in the right valve, while in the left valve they retain their character of ribs to a larger degree. Towards the anterior and posterior ends and at both the left auricles and right posterior one the undulations become narrow ridges. The auricles just mentioned are not sharply demarcated, while the right anterior one is separated from the disc by a deep furrow with a row of pectinidial teeth. A sharp edge is present between the furrow and the disc. The anterior right auricle has four to five radiating ribs crossed by a somewhat foliaceous concentric sculpture, the junctions of the two sculptures being more or less nodulose. The concentric sculpture causes some serration of the anterior right dorsal edge, but otherwise the remaining dorsal edge is rather smooth. The byssal notch is deep. The resilium rather large, rectangular. The soft parts: the mantle is very thin and membranous. The velum forms an extremely broad lobe ventrally, diminishing rapidly towards both ends. The mantle edge has numerous rather small tentacles and a few long and slender ones reaching the edge of the ventral part of the velum. No velar tentacles are present. The foot is very small with a rounded sole and a byssal slit. The byssus is well developed, consisting of numerous threads. There is a byssal retractor in each side, the left one being about twice the thickness of the right one. The "quick" part of the adductor is oblique. The areas of insertion of the two sides are approximately equal in size, and about four times the size of the "catch" part. The gills are very large. The mantle edges appear to be symmetrical. No eyes are present. Measurements: L. of dorsal L H edge type 18.2 20.9 10.7 paratype 3.1 3.4 2.1 Fig. 62. Cyclopecten hadalis n. sp. "Galathea" St. 650. Type. A, interior of umbonal part of the right valve; B, basal part of the right velum; C, foot, byssus and retractor muscles; D, right insertion of the adductor; E, left insertion of the adductor.
Remarks:
The present species differs from C. (H.) undatus Verrill & Smith (see p. 101) in the outline of the shell, being subcircular, while the latter is ovoid with an almost straight posterior edge. There are also conspicuous differences in the shape of the concentric undulations and in the shape of the anterior right auricle. It is also close to C. (H.) graui, but besides the evident differences found in the shell, the latter has a single strong, bipartite byssal retractor on the left side, while in C. hadalis there is one retractor in each side. Distribution : Known only from the Kermadec Trench, 6620-7000 m, 1.3° C. Type: ZMUC. Type locality: "Galathea" St.650.» JØRGEN KNUDSEN, 1970
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«Type material
Holotype (pr) ZMUC BIV-441; Kermadec Trench, 32º20’S, 176º54’W, alive, 6620–6730 m, RRS Galathea (stn 650). Material examined
The holotype (see above). Off Lord Howe Island, 31°34’S, 159°26.5’E, 1808–1828 m (fresh fragments, NIWA I722). Hikurangi Trench, 42º10.5’S, 175º59.4’E, alive, 2602–2677 m, 3 Nov. 1979 (2 v, M.274088; 2 pr, 3 v, several fragments, NIWA S204). Distribution
Off Lord Howe Island, Kermadec Trench (Knudsen 1970) and Hikurangi Trench; alive, 1808–6730 m (Fig. 35). Remarks
The present material is identical to the holotype. The commarginal undulations range from weak to strong, and the radial sculpture is more prominent on the left valve than on the right one. Hyalopecten hadalis is closely similar to H. pudicus (E.A. Smith, 1885) (Atlantic and south-western Indian oceans), in shape, size and sculpture, but has more delicate radial sculpture, and less regular commarginal undulations. Although Knudsen (1970) treated Hyalopecten as a subgenus of Cyclopecten, the two groups differ markedly and indeed belong in separate families (Bernard 1983; Schein 1988, 1989; Dell 1990; Dijkstra 1991, 1995, 2001).» 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. 42, 43]
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Hyalopecten hadalis (Knudsen, 1970); J. C. Melvill & R. Standen, 2008, The recent Pectinoidea of the New Zealand region, figure 36.
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