Cyclopecten zephirus 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. 25, pl. 7, figs. 1-3]
1959 Cyclopecten zephirus Grau, 1959
G. Grau, 1959, plate 7.
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«Shell small, extremely thin, translucent, inequivalve and equilateral, adult specimens averaging 8 mm in height and length; hinge line more than half as long as disk, with beaks protruding slightly above. Right valve moderately convex, with ventral ¼ of disk thinner and reflexed; 55 to 75 fine concentric ridges covering disk, with very minute and irregular radial striae between them; extremely thin outer layer of shell present on some specimens, but apparently always worn off to some extent; anterior auricle moderately large and longer than posterior, with fine concentric ridges; lower half of auricle with convex fold; byssal notch shallow and no ctenolium present; posterior auricle with nearly perpendicular lateral margin, and very finely sculptured by continuations of discal ridges. Left valve more convex than right, and occasionally with one or two faint concentric folds in umbonal area; very fine and widely spaced concentric ridges and slightly stronger and irregular radial ridges often present on upper ⅓ to ½ of disk; auricles of same length as those of right valve, and both with fine concentric ridges.
Holotype: 9 mm in height and length; diameter 1.75 mm; hinge line 5 mm; Allan Hancock Foundation. Type Iocality: 5.5 miles off Long Point, Santa Catalina Island, California, in 400-430 fathoms, gray-green mud; Hancock station 1613-48; October 2, 1948. The species also occurred at 16 additional Hancock stations off southern CaIifornia; of the 17 stations, 13 were in the San Pedro Basin (between the mainland and Santa Catalina Island), 2 just north of the basin and 2 just west of the island. Remarks: This is the thinnest and most fragile species of Pectinidae known to the author. The reflexed ventral portion of the right valve is even thinner than the rest of the disk, and it is impossible to separate the valves without that portion breaking off. On the left valve of many specimens a deep water serpulid is found: Protis pacifica Moore (1923, p. 253). From one to five specimens may be living on a single valve, "... usually directed so that the oral aperture of the annelid is at or near the siphonal end of the mollusk." (Hartman, 1955a, p. 52) Geographically this species seems to be unusually restricted, for the stations at which it was found were all within an area bounded by north latitudes 33° 14' and 35° 54' 09", west longitudes 118° 17' 58" and 119° 10' 15". Apparently it does not range very far beyond the above limits, for it has not occurred in any of the extensive collecting by Hancock expeditions in adjacent areas. Its bathymetric range is also rather restricted, the minimum depth recorded being 400 fathoms, the maximum 620. The 13 San Pedro Basin stations were all located in an area of impoverished fauna which was described and discussed by Hartman in 1955b. At the stations in that area the species was found at from 400 to 495 fathoms in gray·green mud, associated with foraminiferans, Protis pacifica, two or more species of the annelid Phyllochaetopterus and, occasionally, glass sponge. At the other four stations it occurred at from 445 to 620 fathoms in gray-green mud, associated with foraminiferans and various annelids. Cyclopecten subhyalinus (E. A. Smith), known only from off southern Chile, is similar to this species, but differs in being less compressed, not having a convex fold on the anterior auricle of the right valve, having distinct radial lirae but not concentric ridges on that auricle, radial and concentric ridges over the entire surface of the left valve, and possessing a deeper byssal sinus. Hancock Expeditions Collecting Stations:
SAN PEDRO BASIN (between southern California mainland and Santa Catalina Island): stations 1613-48, 2303-53, 2327-53, 2330-53, 2332-53, 2333-53, 2363-53, 2388-53, 2420-53, 2422-53, 2740-54, 2800-54, 2801-54, 400-495 fathoms. NORTHWEST OF SAN PEDRO BASIN: Sta. 2964-54, 490 fathoms; 3020-55, 445 fathoms. WEST OF SANTA CATALlNA ISLAND: sta. 2850-54, 620 fathoms; 2970-54, 476 fathoms.» GILBERT GRAU, 1959
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