Euvola galapagensis (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. 152, pl. 56]
1959 Pecten (Oppenheimopecten) galapagensis Grau, 1959
G. Grau, 1959, plate 56.
|
«Shell inequivalve, thin and of moderate size, largest known specimen (the holotype) 44 mm in height and 49 in length; left valve smaller than right and recessed into that valve at ventral margin to depth of 4 mm; hinge line well over half as long as disk. Right valve quite convex, but less so than Pecten vogdesi Arnold; umbo not produced above hinge margin; 15 smooth and gently rounded ribs, with a very shallow riblet adjoining each submargin; interspaces narrower; fine concentric lamellae covering upper half of disk, with very fine growth striae below. Interior of disk with grooves corresponding to external ribs, becoming shallower toward umbo; reverse surfaces of interspaces flattened and (near ventral margin) angulately ridged; auricular crura next to submargins small and elongate; cardinal crura low and flat. Anterior auricle rather large, flat, and with margin slanting inward from hinge line to byssal notch; weak convex fold just above disk; 3 or 4 small radial ridges above fold; byssal notch shallow and ctenolium of 3 to 5 teeth; auricle covered with fine wavy concentric lamellae projecting above hinge line; posterior auricle rather large and high, with margin slanting inward from hinge margin to disk; gently convex, with shallow concave area halfway between hinge margin and base of auricle; several faint radial ridges in juvenile stage, obsolete at maturity; surface covered with fine concentric lamellae projecting above hinge line. Left valve with pronounced depression of central area; 14 shallow ribs, rounded but somewhat flattened on top; juvenile specimens with two narrow ridges adjoining each submargin, ridges becoming almost completely obsolete at maturity; interspaces wider than ribs. Both auricles rather large, concave, and with margins slanting inward from hinge margin to disk; several indistinct radial ridges present. Surface of disk and auricles covered with fine concentric lamellae, continuous and unbroken from hinge margin of anterior auricle to that of posterior auricle; lamellae always inclined in direction of margins. Color of right valve: disk mostly white, with pale brown mottling on umbo; auricles pale brown: interior white, except for few streaks or blotches of pink or rose along submargins and on auricles. Left valve light brown, dark brown or rose, mottled with lighter and darker colors; auricles white, yellow-brown or rose-pink; interior mostly white, with dark brown or rose at ventral margin and blotches of brown and purple along submargins and in umbonal area.
Hololype: 44 mm in height and 49 in length; diameter 15 mm; hinge margin 29 mm: Allan Hancock Foundation. Type locality: Tagus Cove, Albemarle Island, Galapagos Islands, in 10-18 fathoms, sand and shell; Hancock station 157-34; 0° 16' 08" S, 91° 22' 38" W; January 15, 1934. This species also occurred at the following Galapagos stations: 143-34, off Wenman Island, 100-150 fathoms, coral and nullipores; 147-34, Tagus Cove, Albemarle Island, 30 fathoms, rock, coral, nullipores; 149-34, same place, 20 fathoms, rock and nullipores; 172-34, Stephens Bay, Chatham Island, 12 fathoms, rock, boulders, gorgonoids: 182-34, off James Bay, James Island, 30 fathoms, coarse sand; 201-34, off Gardner Bay, Hood Island, 25-35 fathoms, rock. Remarks; This species is quite distinct from Pecten vogdesi Arnold, although obviously related. The most apparent differences are the white right valve, sharply angled auricles and number of ribs. Other distinctions are the longer hinge line, less convex right valve, uninflated umbo of that valve, absence of intercalary riblets on the left valve, profuse lamellae on that valve and coloring of both valves. From P. hancocki it can be distinguished by the length of the hinge line, larger and sharply angled auricles, lower and fjatter ribs of the left valve, number of ribs (P. hancocki having 1 or 2 more on each valve), less complex surface sculpture of the left valve, nearly smooth right valve and different coloring. The holotype is the largest specimen found, but it does not seem to be mature; the average size of other species in the subgenus would indicate that its maximum height may be from 70 to 80 mm. This species is apparently restricted to the Galapagos Islands. Neither Pecten vogdesi nor P. hancocki have been recorded from the area.» GILBERT GRAU, 1959
|
«Background.-- Euvola galapagensis (Fig. 6.1-6.6) was originally described by Grau (1959) as Pecten (Oppenheimopecten) galapagensis. As discussed above in the section on Leopecten, the genus name Pecten is now used in a more restricted sense and, as applied to extant species, occurs only in the eastern Atlantic and Indo-Pacific. 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.
Two other extant species of Euvola occur in the eastern Pacific. One, the well-known E. vogdesi (Arnold, 1906), ranges throughout the Gulf of California and from the Pacific side of Baja California at about 28°N southward to Ecuador (1°S) in depths from 4 to 220 m (Bernard, 1983; Coan et al., 2000). The other, E. perula (Olsson, 1961), ranges from about 28°N on the west side of Baja California (LACM 71-158) southward to northernmost Peru (4°S) and extends into the southern Gulf of California as far north as Las Animas Bay (28°N, USNM 818577). Depth records range from intertidal to 73 m (Bernard, 1983, and data from USNM and LACM collections). Two extinct species, E. slevini (Dall and Ochsner, 1928) and E. insula (Dall and Ochsner, 1928), are based on specimens found on Isla Santa Cruz (Indefatigable) Island in the Galápagos Islands. Extant species of Euvola are more numerous in the tropical western Atlantic and Caribbean than in the eastern Pacific. A coarsely ribbed species, E. raveneli (Dall, 1898), occurs from about Cape Hatteras, North Carolina, southward throughout the Gulf of Mexico and Caribbean to Guyana and Surinam but is apparently most common in the Gulf of Mexico. Depths range from 9 to 200 m. Euvola ziczac (Linnaeus, 1758), a species with very low or obsolete ribs, has an even more extensive geographic range, extending southward to southern Brazil (about 28°S) but is most abundant in the Caribbean region. It lives at depths from less than 1 m to about 75 m. Both of these species occur on sandy or silty substrates in bays and the open sea. Euvola laurenti (Gmelin, 1791), a less convex derivative of E. ziczac, is restricted to the Caribbean coasts of Central America and is also found in Jamaica and Cuba. Extant ‘‘Amusium’’ papyraceum (Gabb, 1873), which was found by Waller (1991) to be derived from the E. ziczac-laurenti lineage rather than to be related to true Amusium Röding, 1798, occurs on muddy substrates along the mainland coasts of northern South America, Central America, and the northern Gulf of Mexico. Finally, a delicate thin-shelled species, E. chazaliei (Dautzenberg, 1900), occurs at depths of 1–221 m in the tropical western Atlantic and Caribbean, and its closely related sister species, E. turtoni (E. A. Smith, 1890), lives at St. Helena Island, in the central South Atlantic. All of the extant species of Euvola have umbonate larval shells with a small prodissoconch-I/II ratio, suggesting a planktotrophic mode of larval development. The evolutionary origin of E. galapagensis has not previously been considered. Grau (1959) noted the obviously close relationship of the Galápagos species to E. hancocki of Cocos Island while also observing (p. 155) that the latter ‘‘is quite distinct from its nearest relative, Pecten vogdesi.’’ Dall and Ochsner (1928, p. 118) thought that one of the Galápagos fossils that they described as new, E. slevini, was similar to Pecten hemphillii Dall, 1878, from the Pliocene of southern California and ‘‘apparently not so near any of the typical Pectens of the Panama region.’’ [Pecten hemphillii was found to be a junior synonym of Pecten bellus (Conrad, 1856) by Hertlein and Grant (1972, p. 175); see also Moore (1984, p. B68).] The other Galápagos fossil, P. insulus Dall and Ochsner, 1928, was described from the same beds on Isla Santa Cruz. It was not recognized as a close relative of P. slevini but rather was compared to Oligocene Antillean species.» 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. [p. 938, 940]
|
Euvola galapagensis (Grau, 1959); T. R. Waller, 2007, Pectinidae of the Galápagos Islands, figures 6.1-6.6.
|