Euvola marensis (Weisbord, 1964)
WEISBORD, N. E. 1964. Late Cenozoic Pelecypods from Northern Venezuela. Bulletins of American Paleontology, 45 (204): 1-564, pls. 1-59. [p. 136, pl. 14, figs. 2-3]
1964 Pecten (Amusium) marensis Weisbord, 1964
N. E. Weisbord, 1964, plate 14.
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«The following description pertains to the left valve. Shell small, thin, subtranslucent, orbicular, a little higher than wide, subequilateral. Ventral margin nearly semicircular, the dorsal margins diverging at an angle of about 109 degrees. Auricles subequal, both ears depressed slightly below the plane of the disk, the anterior one more so than the posterior; lateral margin of anterior ear subtruncate, that of the posterior hardly curved, both ears marked with barely visible concentric hneations. Hinge line straight. Along the inner margin of the posterior ear there is a fairly sharp ridge or crura, but the inner margin of the anterior ear is poorly defined. Disk flattish, with a faint radial depression on either side, the posterior depression slightly more pronounced. Chondrophore triangular, relatively shallow. Internally there are about 20 subequal to unequal sets of feeble radiating lirae or ribs, arranged generally in pairs, extending from the margins to the upper part of the disk where they become obsolescent. The exterior of the valve is smooth but marked with faint concentric lineations, and through the shell there are revealed faintly the internal lirae.
Dimensions.— Holotype (G326a), left valve, height 19 mm.; width 18.1 mm.; thickness 0.8 mm. Paratype (J326a), left valve, height 13 mm.; width 12.5 mm.; thickness 0.7 mm. Type locality.— Lower Mare at W-14, on hillside above west bank of Quebrada Mare Abajo. One young left valve, the holotype. Other localities.— Lower Mare formation, in small stream 100 meters west of Quebrada Mare Abajo. One juvenile left valve, the paratype. Comparisons.— Of the various species of Amusium mentioned in the immediately preceding pages the ones nearest P. marensis, n. sp. are P. papyraceus (Gabb), P. mortoni Ravenel, and P. luna Brown and Pilsbry. In the Cabo Blanco collection is a left valve of P. papyraceus from the Catia member of the Playa Grande formation which is just about the same size as P. marensis, n. sp. from the Mare formation, and though they appear much the same the following differences may be noted: P. papyraceus is a little wider than high, P. marensis a little higher than wide; the divergence of the dorsal margins is 115 degrees on the Catia P. papyraceus, 109 degrees on the Mare P. marensis; the Catia P. papyraceus has the thicker shell, a few more internal lirae than P. marensis, and the cardinal crurae are broader. P. mortoni is a circular shell, and unlike those of P. marensis which are somewhat sunken, the auricles are separated from the disk by a faintly impressed groove. In P. luna, according to Olsson (1922, p. 377), the internal ribs are in pairs and spaced at intervals nearly twice the width of the pairs of ribs themselves, whereas in P. marensis the subequally spaced rib-pairs and interspaces are about equal in width.» NORMAN EDWARD WEISBORD, 1964
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«Within Euvola Coan et al. (2000) mentioned Leopecten as useful subgenus. The differences between the type species OD Euvola, E. ziczac and a typical Leopecten E. diegensis appear quite significant. Following Dijkstra, in addition to diegensis also stillmani and sericeus are attributed to Leopecten. Furthermore, chazaliei is considered closer to Leopecten.
On the other hand, it is hard to accept, that marensis and laurentii should be mere Euvola. Further work and especially phylogenetic analysis appear necessary. Marensis occurs from Florida to N. Brazil, laurentii from Florida to Venezuela. Raines & Poppe (2006) well treated these two species. Marensis from Honduras and Alabama are indeed the same. It appears that Macsotay & Campos, 2001 misinterpreted marensis and redescribed true laurentii again as Pecten (Euvola) amusoides from Venezuela.» HUBER, M. 2010. Compendium of Bivalves. 901 pp. + 1 CD-ROM. ConchBooks. Hackenheim, Germany. [p. 624]
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«The Euvola clade originated later in the Miocene, probably from an Amussiopecten species that was present in the Tertiary Panamic region in the early Miocene, this region at that time being a single biotic province combining the Caribbean and tropical eastern Pacific provinces before the closure of the Panamanian land bridge (Woodring, 1965). The so-called ''Amusium papyraceum" which now lives in the Caribbean and Gulf of Mexico is a member of the Euvola clade and is not a true Amusium, nor is it conspecific with true Amusium papyraceum from the Miocene of the Dominican Republic, which is a true Amusium. Recent research (Waller, in preparation) has shown that the extant ''A. papyraceum" is in fact two species. One of these is limited in its range to the Atlantic and Caribbean off northern South America from the mouth of the Amazon westward to western Colombia (vicinity of the Guajira Peninsula). The second is limited to the western and northern Gulf of Mexico from Campeche Bay to the shelf off Alabama, with minor populations also occurring off eastern Florida. Pending publication of a detailed account of the comparative morphology and taxonomic nomenclature of these species, the northern one is referred to Euvola species a, and the southern species is tentatively referred to Euvola marensis (Weisbord, 1964). The latter name was based by Weisbord on a few juvenile fossil specimens (height of holotype only 19 mm) from the Playa Grande Formation, which is now considered to be Pleistocene in age (Bermudez, 1980). I cannot agree that the features considered by Weisbord (1964) to be diagnostic for E. marensis are outside the variation of the extant species living off Venezuela. Venezuelan fossils collected by Weisbord from Pleistocene deposits stratigraphically below those containing E. marensis and identified by him as "Pecten (Amusium) papyraceus (Gabb)' are identical to specimens of the species that now lives in the southern Caribbean and Atlantic off South American shores.
Thus far the Venezuelan fossils are the only records of the past history of Euvola marensis; no fossils of Euvola species a have been found, suggesting that the origin of these species is no older than Pleistocene. The closest living relative of these species is clearly Euvola laurenti (Gmelin, 1791), a Caribbean species which is intermediate in shell shape and ribbing pattern between Euvola ziczac and the so-called ''Amusium'' species. Of the two extant ''Amusium'' species, the northern one, Euvola species a, appears to be derived from the southern one, Euvola marensis, because the left valve of the former is more inflated and thus further removed from flattened or concave left valve found in its Euvola ancestry.» WALLER, T. R. 1991. Evolutionary relationships among commercial scallops (Mollusca: Bivalvia: Pectinidae). In: Shumway S. E. (ed.), Scallops: biology, ecology and aquaculture. Developments in Aquaculture and Fisheries Science, Elsevier, Amsterdam, 21: 1-73. [p. 41]
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Euvola marensis (Weisbord, 1964); B. K. Raines & G. T. Poppe, 2006, A Conchological Iconography, The Family Pectinidae, plate 114, figures 1, 2, 5
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