Euvola hancocki (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. 154, pl. 57]
1959 Pecten (Oppenheimopecten) hancocki Grau, 1959
G. Grau, 1959, plate 57.
|
«Shell inequivalve and of moderate size, known specimens averaging 43 mm in height and 45 in length; obliquity rather pronounced, with disk produced posteriorly and posterior submargins longer and more steeply angled than anterior ones; left valve smaller and recessed into right valve at ventral margin to depth of 3 or 4 mm; hinge line less than half as long as disk. Right valve quite convex, but less so than Pecten vogdesi Arnold; umbo seldom produced above hinge margin; 16 or 17 strong rounded ribs, with a small riblet adjoining each submargin; interspaces narrower; disk covered by very thin and concentrically striate layer of shell, with fine concentric lamellae beneath; lamellae visible where outer layer worn off: on portions of submargins and in interspaces of top one-third to two-thirds of disk. Interior of disk with moderately deep grooves resulting from external ribs; reverse surfaces of interspaces with edges angulated and occasionally thickened, but usually not; small elongate nodule at base of anterior auricle and larger one at base of posterior; cardinal crura rather large in arca but not strongly produced. Anterior auricle rather small and shallowly convex; fasciole narrow, with concentric fold above it; 2 or 3 stronger radial riblets above fold and one or two very weak ones above them; byssal notch very shallow; ctenolium of 3 to 5 teeth present until shell reaches height of about 25 mm. absent in adult specimens; surface of auricle with same outer layer as disk and very fine (but seldom visible) concentric lamellae beneath. Posterior auricle with varying number of very faint radiating ridges; about 1 mm shorter than anterior auricle and with same surface sculpture. Left valve almost flat, central portion being only slightly depressed; 15 or 16 strong rounded ribs, with a low riblet adjoining each submargin; interspaces a Iittle wider; surface originally covered by same thin striate layer as right valve, but outer layer worn off of upper one-half to two-thirds of tops of ribs and almost completely off of interspaces, thus exposing a larger number of lamellae than are visible on right valve. Interior of disk grooved as result of external ribs, grooves becoming shallower toward umbo; reverse surfaces of interspaces flat and angulately ridged near ventral margin; two small nodules at base of anterior auricle and one rounded one with depressed center at base of posteriori cardinal crura as on right valve. Both auricles same length as corresponding auricles of right valve and having varying number of low riblets, most prominent near hinge line; sculpture as on disk, but with major portion of outer layer usually worn off. Color of right valve: mostly white, with umbonal area (and occasionally auricles) pale orange to pink-orange; interior grooves white, reverse surfaces of interspaces ecru, auricles and submargins pink or rose-pink. Color of left valve: orange or red-orange (sometimes mottled with white) in umbonal region, shading to pale brown or red~brown near ventral margin; tops of ribs (on lower one-third to one-half of disk) pale ecru or gray-white.
Holotype: 47 mm in height and 49 in length; diameter 17 mm; hinge line 22 mm; Allan Hancock Foundation. Type locality: Chatham Bay, Cocos Island, Costa Rica, in 47 fathoms, coarse white sand; Hancock station 780b-38; 5º 33' 50" N, 86º 58' 45" W; January 14, 1938. The species also occurred off Nuez Island, Cocos Island, in 31-50 fathoms, coralline; Hancock station 773-38. Remarks: This species is quite distinct from its nearest relative, Pecten vogdesi Arnold. The most apparent differences are the white right valve with pale orange or pink-orange umbo and the smaller number of ribs, P. vogdesi having from 3 to 5 more. Other distinguishing features are the oblique disk, shorter hinge line, less convex right valve, less inflated umbo of that valve, rounded ribs and absence of intercalary riblets on the left valve, complex surface sculpture and the exterior and interior coloring. Although the holotype is the largest specimen found, it is not fully adult; judging by the other species in its subgenus it probably attains a maximum height of from 70 to 80 mm. Apparently this species is restricted to the Cocos Island area. Pecten vogdesi did not occur at any of the 7 Cocos Island Hancock stations in 1933 nor the 11 in 1938, and almost certainly does not live in the area. However, it is plentiful off Costa Rica, a little over 300 miles eastward. In appreciation of the extensive support he has given marine research, this species is dedicated to Captain Allan Hancock.» GILBERT GRAU, 1959
|
«The name Oppenheimopecten von Teppner, 1922 has been applied to morphotypes in which the right valve is more deeply convex than in the type species of Pecten s.s., but I regard it as a junior synonym of that genus, as did Fleming (1957). Grau (1959), in a study of eastern Pacific pectinids collected by the Hancock Expeditions in the 1930s, found E. galapagensis at seven Galápagos stations within dredging depth ranges of 22-274 m. He also discovered a second new species in the Hancock material from Cocos Island, which he named P. (O.) hancocki (Fig. 6.7-6.12) and which is also reassigned here to Euvola. It is known only from Cocos Island, where it was dredged in depths of 57-91 m.»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands. Journal of Paleontology, 81 (5): 929–950, pls. 1-18. [p. 938]
|
Euvola hancocki (Grau, 1959); T. R. Waller, 2007, Pectinidae of the Galápagos Islands, figures 6.7-6-12.
|