Hyalopecten kurilensis Kamenev, 2016
KAMENEV, G. M. 2016. Three new species of the genus Hyalopecten (Bivalvia: Pectinidae) from the abyssal and hadal zones of the North-western Pacific Ocean. Journal of the Marine Biological Association of the United Kingdom, Oct. 2016: 1-18, figs. 1-9. [p. 13, figs. 8, 9]
2016 Hyalopecten kurilensis Kamenev, 2016
G. M. Kamenev, 2016, figures 8, 9.
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«TYPE MATERIAL AND LOCALITY
Holotype: one adult specimen (RV ‘Vityaz’, cruise 39, station 5623, abyssal plain adjacent to Kuril-Kamchatka Trench, North-western Pacific; coordinates: 45°26′N 154°59′E; water depth: 4995–5045 m, Galathea trawl) (ZMMU Ld-3059); coll. L.A. Zenkevich, 19 August 1966. OTHER MATERIAL EXAMINED
Damaged specimen (IO RAS) from holotype locality. DIAGNOSIS
Shell small (to 9.7 mm in height), thick, slightly higher than longer, inequilateral. Umbonal angle 105°. Auricles large, unequal in size and shape. Right and left valve discs with 5–6 wide, commarginal undulations and reticulate sculpture from about 40 widely spaced, well-developed, radial ribs and more closed, commarginal, lamellate, overlying riblets. Anterior auricle of right valve demarcated from disc; sculptured with four distinct radial ribs and coarse, closely spaced, commarginal, overlying, lamellate ribs. Anterior auricle of left valve separated from disc by a shallow sulcus; sculptured with closely spaced, lamellate, commarginal ribs and a few, weak, wide radial ribs. Posterior auricles weakly separated and continuous with disc; sculptured with widely spaced, commarginal, lamellate ribs. Byssal fasciole broad. Byssal notch moderately deep, broadly rounded. Active and inactive ctenolium well-developed. Prodissoconch large (length 260 μm), D-shaped. DESCRIPTION
Shell small (to 9.7 mm in height), opaque, thick, hard, inflated, slightly higher than longer (H/L = 1.032), inequilateral (beaks slightly posterior to midline, A/L = 0.521), inequivalve (left valve more convex than right valve). Shell disc oblique, slightly drawn out anteriorly. Dorsal shell margin straight. Anterior shell margin rounded. Posterior shell margin slightly convex, smoothly transitioning to rounded ventral shell margin. Auricles large (AL/L = 0.596), anterior auricle larger and longer than posterior (AAL/AL = 0.571). Umbonal angle 105°. Right and left valve discs with wide, commarginal undulations (five in right and six in left valve) strongly smoothed near beak and almost indiscernible. Undulations in form of broad steps with a rounded edge widening (up to 1.7–1.8 mm) towards ventral shellmargin. Valve discs with reticulate sculpture from about 40 widely spaced, well-developed, rounded, radial ribs (interstices broader than ribs, 0.2–0.5 mm in disc centre) and more closely spaced, commarginal, thin, lamellate, overlying riblets (with interspaces 0.2–0.3 mm) becoming denser in lower part of undulations. Anterior auricle of right valve slightly twisted to the right, sharply demarcated from shell disc by a sharp, thin suture and a long, strong ctenolium. Surface of auricle with four distinct radial ribs on dorsal half of auricle and coarse, closely spaced, commarginal, overlying, lamellate ribs forming serration of auricle dorsal margin. Byssal fasciole broad. Byssal notch moderately deep, broadly rounded. Active ctenolium short. Anterior auricle of left valve separated from disc by a shallow sulcus; anterior auricle margin extending vertically down. Surface of auricle with closely spaced, lamellate, commarginal ribs, forming indistinct serration of auricle dorsal margin, and a few indistinct, weak, wide radial ribs. Posterior auricle of right and left valves weakly separated from shell disc; dorsal and posterior auricle margins producing a rounded acute angle; sculptured with widely spaced, commarginal, thin, lamellate ribs, forming indistinct serration of auricle dorsal margin. Prodissoconch large (length 260 μm), smooth, D-shaped, convex, distinct, sharply separated from shell disc. DISTRIBUTION AND HABITAT (FIGURE 4)
This species was recorded at the abyssal plain adjacent to the Kuril-Kamchatka Trench (North-western Pacific) at 4995–5045 m depth. COMPARISONS
Hyalopecten kurilensis is most close to Hyalopecten arntzi, Hyalopecten neoceanicus and Hyalopecten profundicola in terms of the dimensions, shape and proportions of the shell, as well as the presence of cancellate sculpture (Figure 5, Table 2). However, unlike H. arntzi, H. kurilensis has a thick, inflated and opaque shell with much fewer and much wider commarginal undulations, a much smaller number of wider and more widely spaced radial ribs, and well expressed widely spaced lamellate, commarginal ribs. Hyalopecten kurilensis is distinguished from H. neoceanicus by having a less drawn-out anterior part of the shell, the beaks less displaced posteriorly, non-pointed and smaller auricles, a rounded byssal notch, and fewer rounded and more widely spaced radial ribs. Hyalopecten kurilensis differs from H. profundicola in having a shell less drawn-out anteriorly, less posteriorly displaced beaks, shorter auricles, commarginal undulations, and fewer wider and more widely spaced radial ribs. ETIMOLOGY
The specific name ‘kurilensis’ derives from the name of the Kuril Islands, at the latitude of which it was found at the abyssal plain of the Pacific Ocean. REMARKS
As was the case with Hyalopecten abyssalis, despite the relatively large number of benthic samples collected at the abyssal plain of the North-western Pacific, Hyalopecten kurilensis was only found at one station. Like H. abyssalis and Hyalopecten profundicola, this species may also fall under the category of ‘rare’ species, forming sparse populations on the abyssal plain of the North-western Pacific.» GENNADY M. KAMENEV, 2016
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