Cyclopecten Verrill, 1897
VERRILL, A. E. 1897. A study of the family Pectinidae, with a revision of the genera and subgenera. Transactions of the Connecticut Academy of Arts and Sciences, 10: 41-95, pls. 16-21. [p. 70]
«Cyclopecten, gen. nov.
Types, Pecten pustulosus Verrill; P. imbrifer Loven. Plate XVI. fig. 1. Plate XIX. figs. 1-4.
Shells thin, rounded, scarcely oblique, with symmetrical auricles and simple margins. The two valves are unlike in sculpture. The right valve is a little flattened and upturned at the flexible margin, so as to fit tightly against the upper valve. The thin lower valve has, in the typical species, regular, thin, elevated, concentric lamellae, which aid in the adaptation of the edge to that of the upper valve; the margin is usually flattened or bevelled. The upper (left) valve is radially sculptured, rarely smooth; it usually has radial rows of arched scales, pustules, or points, and also concentric raised lines; it is sometimes cancellated. No radial ribs, nor interlocking points at the margin. Auricles well developed, subequal, angulated and welldefined at both ends; byssal notch well defined; few or no pectinidial teeth. Cardinal folds single, rather feebly developed, often cross-lined. Eyes few. Byssus small, and of few threads.
The species of this group have usually been referred to Pseudamusium, but they differ widely from the typical forms of that group, such as P. exoticum, P. dispar, etc., in which the valves are of nearly equal size, with simple edges that come evenly together without flexure of the lower one, and in which the auricles are small and nearly equal.
This genus includes a large number of small species, mostly from deep water. Among these are the following: C. imbrifer (Lov.), northern coasts of Europe; C. pustulosus (Ver.) (cut, fig. 1), (pl. xix, figs. 3, 4); C. subimbrifer (V. and B., see p. 84), 121 fath.; C. leptaleus (Ver.), 142 fath.; C. nanus V. and B.; (pl. xvi, figs. 12-12c), the last four are from deep water off the eastern coast of the United States; G. retlculus (Dall); C. simplex Ver. (pl. xvi, fig. 1, xix, figs. 1, 2); and C. Culebrensis (Smith), 390 fath., are from the West Indies; C. Murrayi (Smith), 1400 fath., off Australia; C. clathratus (Mart.), 120 fath.; C. suhhyalinus (Smith), 400 fath.; and C. distinctus (Smith), 100 fath., from the Antarctic regions; C. Kermadeciensis (Smith), 600 fath., off Kermadec I. C. orbicularis (Sowerby), which occurs on the west coast of Africa, living among, and usually attached to, floating fucoids {Sargassum, etc.), near the shore, appears to belong to this genus. It has concentric sculpture on both valves; that on the left forms raised scale-like lamellae. The shell is hyaline. The valves close tightly by the upturning of the edge of the right one. According to Dr. Charbonnier (Journ. de Conch., ser. II, vol. iv, p. 261) this species swims about very actively, but attaches itself very firmly and quickly (in 15 minutes), to floating algae by a byssus of several threads. When at the bottom of the glass vessel, it creeps about by means of its foot.» ADDISON EMERY VERRILL, 1897
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A. E. Verrill, 1897, A study of the family Pectinidae, with a revision of the genera and subgenera, plates 16, 19. Cyclopeden simplex V., sp. nov., plate 16, figure 1, plate 19, figures 1, 2; Cyclopecten parvus V. and Bush., plate 16, figures 12, 12a-12c; Cyclopecten pustulosus, plate 19, figures 3, 4.
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H. H. Dijkstra & A. G. Beu, 2018, Living scallops of Australia and adjacent waters, figure 17; Cyclopecten kapalae Dijkstra, figures 19A-19C, 19E, 19H; Cyclopecten powelli Dell, figures 19D, 19F, 19G, 19I.
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«Cyclopecten Verrill, 1897
Cyclopecten Verrill, 1897: 70. Type species (by subsequent designation, Sykes et al., 1898): Pecten pustulosus Verrill (1873: 14); Recent, near Georges Bank, off Newfoundland, Canada, 274 m.
Xenamussium Oyama, 1944: 244 (proposed as a subgenus of Propeamussium). Type species (by original designation): Pecten hoskynsi Forbes (1844: 146, 192); Recent, “Asia minor” [= off Turkey]. Diagnosis. Shell equivalve, small, circular in most species, laterally compressed, prodissoconch smooth, weakly inflated; left valve of most species sculptured with radial and/or commarginal costellae or striae, right valve with commarginal lamellae; auricles unequal; byssal notch well-developed; without internal radial riblets.
Distribution. Paleocene?, Oligocene–Recent (Waller, 2011). Cosmopolitan, subtidal to hadal (Hayami & Kase, 1993: 59). Most representative Cyclopecten species from the Indo-West Pacific region, however, live in deep water (Habe, 1977; Bernard, 1983; HHD, unpubl. data).
Discussion. Verrill (1897: 70) mentioned in his description “few pectinidial teeth [= ctenolium], byssus and byssal threads”, which are based on “Cyclopecten” circularis (G. B. Sowerby I, 1835) [= Lissochlamys exotica (Dillwyn, 1817), a pectinid species mistakenly included by Verrill]. A ctenolium and byssus are not present in Cyclopecten. Many Cyclopecten species have been described and placed in different genera, for example Delectopecten (a pectinid genus) (Hertlein, 1969; Knudsen, 1970; Habe, 1977; Bernard, 1978; Rombouts, 1991) or Palliolum (a pectinid genus) (Abbott, 1974, in part). Several described “Cyclopecten” species from the subantarctic region belong in Cyclochlamys (see below) (Dijkstra, unpubl. data).
The morphological characters of Cyclopecten are closest to those of Parvamussium, although Cyclopecten species are easily distinguished by their lack of internal riblets. As Hayami & Kase (1993: 59) suggested, Cyclopecten possibly was derived from Parvamussium through paedomorphosis. The shell characters of Xenamussium are identical to those of Cyclopecten, and in our opinion these names are synonyms.» 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. [148, 149]
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