Cyclopecten ambiannulatus Schein, 1989
SCHEIN, E. 1989. Pectinidae (Mollusca, Bivalvia) bathyaux et abyssaux des campagnes BIOGAS (Golfe de Gascogne). Systématiqueet biogéographie. Annales de l'Institut Océanographique, 65: 59-125 [p. 86, pl. 4, figs. 1-9, 11, 12]
1989 Cyclopecten ambiannulatus Schein, 1989
«Distribution
Off western Iceland (62°–67° N, 20°–28° W), living in 503–1408 m (Map 9). A single specimen is supposed to come from station 2740, but considering the locality, so far further north than the others, it must be considered uncertain, perhaps mislabelled. Description
Shell (Figures 1G,H, 5H,I) up to ca. 7 mm high, fragile, transparent to opaque, circular, left valve slightly more convex than right valve, anterior auricles slightly larger and more demarcated from disc than posterior ones; umbonal angle ca. 110°; internal ribs lacking, colour whitish. Prodissoconch (Figure 2I), length 185 μm, colour white. Both valves (Figures 4E,F, 8E,F) sculptured with uniform and closely spaced commarginal lamellae (ca. 10 per mm on the central part of the disc), commencing in early growth stage directly below the prodissoconch boundary and extending towards the ventral margin. Granular intercalated microsculpture. Similar sculpture on the auricles, except anterior auricle of right valve, which is almost smooth. Posterior auricle of right valve continuous with disc, anterior auricle demarcated. Hinge line straight. Byssal notch moderately deep, byssal fasciole narrow, suture somewhat folded, ctenolium lacking. Discussion
The BIOICE specimens resemble Cyclopecten ambiannulatus Schein, 1989, known from the temperate eastern Atlantic (44588N). Both species are somewhat similar in shape, size and colour, but differ in sculpture. Cyclopecten orbiculatus has more closely and regularly spaced commarginal lamellae on the left valve, and lacks interstitial radial sculpture. Cyclopecten ambiannulatus has widely spaced lamellae in young specimens and closely spaced ones with delicate interstitial radial lines in adult and subadult specimens (Schein 1989: pl. 6, figures 1–5). Cyclopecten cincinnatus Dijkstra & Gofas, 2004, known from the Mid-Atlantic seamounts (30–34° N) differs from C. ambiannulatuus in having much more widely spaced commarginal lamellae on the central part of the left valve (ca. 2 per mm, in C. ambiannulatus 8–10), and in having prominent commarginal lamellae on the anterior auricle of the left valve (in C. ambiannulatus very weak or lacking). Some specimens of Cyclopecten hoskynsi (‘var. lamellosus’ in Jensen 1912) have prominent commarginal lamellae also on the left valve, but these are undulating, widely spaced and irregularly developed, and originate from incompletely formed vesicles. Such specimens can be distinguished from C. ambiannulatus by C. hoskynsi having very small posterior shell ears.» DIJKSTRA, H. H., A. WARÉN & G. GUDMUNDSSON. 2009. Pectinoidea (Mollusca: Bivalvia) from Iceland. Marine Biology Research, 5: 207-243, figs. 1-20. [p. 218]
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Cyclopecten ambiannulatus Schein, 1989; H. H. Dijkstra, A. Warén & G. Gudmundsson, 2009, Pectinoidea (Mollusca: Bivalvia) from Iceland, figures 1G, 1H, 5H, 5I.
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