Cyclopecten acutus Grau, 1959
GRAU, G. 1959. Pectinidae of the eastern Pacific. Allan Hancock Pacific Expeditions, 23: viii, 308 p., pls. 1-57. University of Southern California Press. Los Angeles, California. [p. 31, pl. 10, fig. 2]
1959 Cyclopecten acutus Grau, 1959
G. Grau, 1959, plate 10.
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«Shell very small, rather thin but opaque, glossy, slightly inequivalve and equilateral, largest specimen found (a left valve) measuring 4 mm in height; hinge line usually same length as disk but occasionally somewhat shorter; beaks protruding slightly. Right valve moderately convex (slightly less than left valve) and covered by a thin transparent layer of shell extending beyond entire margin of valve except in center of hinge margin; only sculpture on disk consisting of extremely faint concentric ridges. Anterior auricle very slightly longer than posterior and with numerous line concentric lamellae; byssal notch rather shallow and no ctenolium. Posterior auricle pointed and finely concentrically lamellose. Left valve moderately convex and covered by same transparent layer of shell as right valve, layer also extending beyond entire margin except above hinge line; 6 to 8 prominent rows of concentric lamellae on disk in very young stage, in adult stage either faintly present on umbo only or entirely absent; very minute concentric lines of growth on rest of disk. Anterior auricle slightly shorter than that of right valve, with numerous faint radial ridges and 4 or 5 fine concentric lamellae near the beak. Posterior auricle same length as that of right valve and also pointed, having numerous faint radial ridges. Color of right valve: white or yellow-white; left valve: White or yellow-white, with streaks or blotches of yellow or yellow-brown.
Holotype: Height and length 3.75 mm; diameter 1.5 mm; hinge line 3.75 mm; Allan Hancock Foundation. Type locality: Off north side of Gorgona Island, western Colombia, in 32 fathoms; Hancock expeditions bottom sample 584; February 24, 1938. The species also occurred in Octavia Bay, western Colombia, in 75 fathoms; Hancock bottom sample 555; January 27, 1938. Remarks: This species is quite distinct. From its nearest relative, Cyclopecten pernomus (Hertlein), it can be separated particularly by its transparent margins but also by its orbicular disk, absence of radial ridges on the left valve, much finer concentric ridges on the right valve and the length and sculpture of the auricIes. From C. cocosensis (Dall) it differs primarily in the transparent margins and also in the shape of the disk, the absence of radial striae and posterior sulcus on the right valves, and the length and sculpture of the auricIes.» GILBERT GRAU, 1959
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