Cyclopecten guppyi (Dall, 1898)
DALL, W. H. 1898. Contributions to the Tertiary fauna of Florida. Silex Beds of Tampa and the Pliocene Beds of the Caloosahatchie River. Part IV. I. Prionodesmacea: Nucula to Julia. 2. Teleodesmacea: Teredo to Ervilia. Transactions of the Wagner Free Institute of Science of Philadelphia, 3 (4): viii, 571-947 p., pls. 23-35 (pls. 36 and 37 in part 5, 1890) [p. 718 & 755, pl. 34, figs. 12-13]
1898 Pecten (Pseudamusium) [sic] guppyi Dall, 1898
W. H. Dall, 1898, plate 34.
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«Oligocene of the Bowden marl, Jamaica, and of the Alum Bluff sand at Oak Grove, Santa Rosa County, Florida, Burns; and in the Pliocene marl of Port Limon, Costa Rica, Hill.
Shell small, suborbicular, moderately convex, smooth, with the surface covered with microscopic Camptonectes striation; ears small, the anterior slightly larger, all with very minute radiation and concentric lines; notch narrow, small, with no ctenolium; interior smooth, without lirae or developed crura; traces of the auricular crura alone perceptible; cardinal margin bearing a sharply cross-striated, very distinct provinculum; basal margins flattened, posterior margin slightly compressed. Alt. 6, lat. 6 mm. The abundance and uniformity of this little shell testify to its adult character. Occasional individuals show a thickened line internally on each side, on the lower edges of the submargins, like some recent species, and also traces of coloration in blotches.» WILLIAM HEALEY DALL, 1898
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«Remarks.— Neither Dall (1898) nor Woodring (1925) recognized that the cotypes of Cyclopecten guppyi represent two distinct species, one with internal ribs and the other without. In the abundant material from the Dominican Republic (Table 1), all of the specimens of Cyclopecten from the Cercado and lower Gurabo formations lack internal ribs and are assigned to C. guppyi. Specimens higher in the section, in the upper Gurabo and Mao formations, have a lateral internal rib on each side of the disk on each valve and are assigned to C. zalaya n. sp. The two species co-occur only in situations involving gravity-flow deposits in which shallower water specimens have been carried into deeper water. The distributions of the two species establish that C. guppyi is the shallower species and C. zalaya the deeper. This conclusion is corroborated by the association of C. guppyi with shallow-water species as well as by the common presence in C. guppyi of severe marginal fracturing repaired during life (Pl. 1, Fig. 8). The presence of these injuries around the entire margin of the disk but not on the auricles suggests damage by shell-nipping predators, not by tumbling in sediment above wave base during severe storms.
Contrary to Dall's description of C. guppyi, "Camptonectes striae," i.e., antimarginal striae, are not present. In the specimens from Bowden, epitaxial crystallization of calcite on the surface of the shells has occurred. On the left valve, this crystallization accentuates the antimarginal grain of groups of crystals in the outer foliated-calcite layer. It is therefore a diagenetic effect and not indicative of actual microsculpture. It is not present in the better preserved material from the Dominican Republic. Also contrary to Dall's description, the cross-ridged apposition zones of the hinge are not a provinculum, a term usually now reserved for the hinge of the prodissoconch. The apposition zones and the first coarse cross-ridges originate on the dissoconch after the end of the prodissoconch stage. Morphological variation in Cyclopecten guppyi mainly involves the degree of expression of radial costellae on auricles. Among specimens from the Dominican Republic, most specimens have barely discernible auricular costellae on the ventral or distal parts of the auricles of the left valve. In the relatively few specimens available from the Bowden Formation, the radial costellae are more developed. The same applies to the presence of weak, widely spaced commarginal lirae on the umbo of the left valve, these being more consistently developed in the Bowden material. There is also variation in umbonal angle within the Dominican Republic material, with many specimens having a somewhat broader angle than that of the Bowden specimens. Pigment patterns of left valves consistently have randomly distributed gray spots on a more opaque, whitish background, with one exception, where opaque white pigment with broad V-shaped indentations in its ventral boundary is present on the umbo of the left valve. Extant Cyclopecten species of small size in tropical waters occur over a broad depth range but are seldom found living at depths shallower than ca. 30 m. Cyclopecten guppyi, however, is commonly associated in the Cercado and lower Gurabo formations with Smaragdia, a neritid gastropod genus that is regarded as a seagrass specialist associated with seagrasses that are commonly restricted to depths < 30 m in low-energy conditions (Costa et al., 2001: 61).» WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [pl. 19, 21]
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Cyclopecten guppyi (Dall, 1898); T. R. Waller, 2011, Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae of the Cibao Valley, plate 1, figures 4-8.
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