Argopecten irradians concentricus (Say, 1822)
SAY, T. 1822. An account of some marine shells of the United States. Journal of the Academy of Natural Sciences of Philadelphia, ser. 1 2 (2): 221-248, 257-276, 302-325. [p. 259]
1822 Pecten concentricus Say, 1822
1835 Pecten circularis G. B. Sowerby I, 1835
1852 Pecten leucophaeus Reeve, 1852
1987 Argopecten irradians taylorae Petuch, 1987
1835 Pecten circularis G. B. Sowerby I, 1835
1852 Pecten leucophaeus Reeve, 1852
1987 Argopecten irradians taylorae Petuch, 1987
Pecten circularis Sow.; G. B. Sowerby II, 1842, Thesaurus conchyliorum, Monograph of the genus Pecten, plate 12, figure 23.
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«SheIl suborbicular, with from eighteen to twenty elevated, rounded ribs, and very numerous simple transverse wrinkles; longitudinal striae, none; one valve somewhat ventricose, pale-yellow, fasciated concentrically with reddish-fuscous or blackish; the other valve convex, brownish-cinereous; auricles subequal; hinge margin rectilinear in each valve; within white.
Length two inches and nine-tenths. Breadth three inches and one-tenth. Inhabits the coast of New Jersey. Var. a. Somewhat more compressed, variegated. Cabinet of the Academy and Philadelphia Museum, and Mr. Hyde's collection. Although this shell is a large species, and is one of our most common shells, yet I cannot perceive that it has been either flgured or described distinctly in any work to which I can refer. The inner margin, particularly between the ribs, is sometimes of a dirty reddish-brown colour. I have not seen this species on the southern coast. The variety occurs on the coast of New England, and several specimens are preserved in Mr. William Hyde's cabinet. One specimen is of a fine bright orange-colour, and on one of the valves only, are the concentric bands of blackish; the margins, which decline from the beaks, are transversely mottled with white. Another has one valve blackish-brown, with about a dozen rather large white spots on the disk, longitudinally disposed, and white transverse variegations on the umbones and beaks; the margins, which decline from the beaks in both valves, are similarly coloured, and varied with transverse white marks; the opposite valve is yellowish-white, with the usual bands. It must. however, be observed, that the epidermis of both these specimens was removed by muriatic acid. It is probable that the examination of numerous specimens, will prove this to be a distinct species, if so, it may be distinguished by the name of P. borealis». THOMAS SAY, 1822
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«The subspecies concept gains strength, however, when it is applied to populations that are separated by distributional gaps or barriers that constrain contact (sensu Mayr, 1969). Waller (1969) described a distributional gap of approximately 764 km (475 miles) between the easternmost population of A. i. amplicostatus and the westernmost population he considered to represent A. i. concentricus, and he proposed that the Mississippi Delta acts as a barrier to genetic interchange between those stocks. Thus, subspecific designations for those populations seem appropriate.
A distributional gap of similar magnitude in the southeastern United States has received less attention, perhaps because it contains no obvious barrier. The northernmost population of bay scallops along eastern Florida is at Palm Beach Inlet (Lake Worth Inlet) (Waller, 1969) near latitude 26°45'N, and the next documented occurrence of the species seems to be at Lockwood Folly Inlet near Cape Fear, North Carolina (Porter, 1974), near 33°50'N; these populations are separated by a minimum distance of nearly 800 km. Even if reports of uncommon occurrence in South Carolina (Clarke, 1965; Shoemaker et al., 1978) and an unsubstantiated report from Georgia (Petuch, 1987) are considered, no population of bay scallops is known in the region between Palm Beach Inlet and the Florida-Georgia border at 30°45'N, a gap of nearly 450 km. Thus, despite reported similarities in shell morphology, the genetic gap between the North Carolina and Florida stocks is not a simple expression of distant populations separated by other, more contiguous populations distributed along a cline. Instead, the bay scallop stocks of Florida (and probably those extending to eastern Louisiana) seem to comprise an aggregation of populations isolated by large distances from other aggregations to the north and to the west, i.e., a subspecies, sensu Mayr (1969). If A. i. concentricus is not appropriate as a name for bay scallop stocks of Florida and the eastern Gulf of Mexico, and if those stocks merit subspecific recognition, then A. i. taylorae Petuch, 1987, is the first available name. Another possibility, Pecten circularis Sowerby, 1835, was shown by Waller (1995) to be a junior synonym of Argopecten irradians concentricus. Dr. Waller informed us (in litt.. 1/30/96) that the holotype of Pecten circularis "compares favorably with North Carolina concentricus in overall shape, auricular shape, rib shape, and rib count, and it differs in these features from Gulf populations."» MARELLI, D. C., W.G. LYONS, W. S. ARNOLD & M. K. KRAUSE. 1997. Subspecific status of Argopecten irradians concentricus (Say, 1822) and of the bay scallops of Florida. The Nautilus, 110 (2): 42-44. [p. 43, 44]
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Argopecten irradians concentricus (Say, 1822); B. K. Raines & G. T. Poppe, 2006, A Conchological Iconography, The Family Pectinidae, plate 265, figures 1-3.
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«We assessed alleged differences between typical Argopecten irradians taylorae and representatives of other bay scallops from peninsular Florida. Based on the results of our electrophoretic and morphometric examinations, we refute those differences and conclude that bay scallops from Rabbit Key Basin do not represent a subspecific taxon distinct from Florida populations of A. i. concentricus.»
MARELLI, D. C , M.K. KRAUSE, W. S. ARNOLD & W. G. LYONS. 1997. Systematic relationships among Florida populations of Argopecten irradians (Lamarck, 1819) (Bivalvia: Pectinidae). The Nautilus, 110 (2): 31-41. [p. 40]
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Argopecten irradians concentricus, figures 4, 6, 7; Argopecten irradians taylorae, figure 4; D. C. Marelli et al., 1997, Systematic relationships among Florida populations of Argopecten irradians.
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«Because the type of Pecten circularis Sowerby I (1835) was incorrectly named a new species by Sowerby and is in fact a specimen of Argopecten irradians concentricus (Say, 1822), Sowerby's name is a junior subjective synonym of the latter.»
WALLER, T. R. 1995. The misidentified holotype of Argopecten circularis. The Veliger, 38 (4): 298-303. [p. 301]
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Argopecten irradians concentricus (Say, 1822); T. R. Waller, 1995, The misidentified holotype of Argopecten circularis, figures 1-4.
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«Description. Shell outline.— Shell attaining moderate size, mature individuals commonly 45 to 70 mm in height, distinctly right-convex (text-fig. 9). Outline of disk roughly equilateral, appearing somewhat opisthocline; disk flanks steep proximally, becoming less steep distally, more or less straight in plane perpendicular to commissure and to disk flank. Disk gapes very narrow to rather wide; posterior disk gape commonly absent.
Outer ligantent and auricles.— Right auricles with dorsal margins extending only very slightly dorsal to outer ligament; free margins forming 90º or obtuse artgles at junctures with outer ligament. Free margins of posterior auricles shallowly sigmoidal in plane of commissure, with main portion of margins forming right angle with dorsal margins. Right anterior auricle with broadly rounded anterior margin; byssal notch of mature individuals moderately deep to rather shallow, with apex angular, truncate, or rounded; ctenolium generally present but commonly weakly developed on larger individuals; byssal fasciole strongly arched in plane perpendicular to adjacent disk flank. Ornament.— Plicae of right valve 15 to 22 in number ( text-fig. 8), with external surfaces high and sharply rounded proximally, becoming lower and rounded, somewhat trapezoidal or semihexagonal in cross section distally. Concentric lamellae on disk generally projecting only in interspaces and on sides of plicae on right valve, commonly extending over plicae on left valve; trend of lamellae across central region of mature valve at heights greater than 40 mm distally convex across interspaces and distally concave across crests of plicae, with additional distally concave arc on inflated sides of trapezoidal plicae; spacing of lamellae in central regions of mature valves rather wide. Disk flanks distinctly costate, with costae similar to auricular costae in amplitude. Color of left valves generally dark and drab gray, brown, or black, sometimes reddish, in a uniform, vaguely mottled, or vaguely concentrically banded pattern. Right valves generally dusky yellowish white, except at umbones, rarely with faint, irregular patches of same color as on left valve. Internal features.— Resilial insertions generally longer than high (mean values of ad/ce of right-valve samples ranging from .75 to .85). Auricular denticles very weakly to rather strongly developed. Cardinal crura moderately to strongly developed. Comparison. A. irradians concentricus differs from A. irradians irradians in having thicker and more convex valves, higher marginal amplitude, and larger resilial insertions relative to valve height although shorter relative to resilial height. Compared to A. irradians amplicostatus, A. irradians concentricus has thinner and less convex valves, a greater number of plicae (text-fig. 8), and a somewhat opisthocline appearance. Stratigraphic range. Lower Pleistocene (Unit A) to present.» WALLER, T. R. 1969. The evolution of Argopecten gibbus stock (Mollusca: Bivalvia), with Emphasis on the Tertiary and Quaternary Species of Eastern North America. The Paleontological Society. Memoir 3 [Journal of Paleontology, 43 (5, supplement)]: 125 pp. [p. 41, 42]
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Argopecten irradians concenticus (Say); T. R. Waller, 1969, The evolution of Argopecten gibbus stock, plate 7, figures11, 12, 14, 15 (above); plate 8, figures 10, 11 (below).
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«Description. Shell up to 95 mm long in specimens examined, width equal to or slightly greater than length, valves not as thin as in A. irradians s. s ., somewhat inflated, and sculptured with 17 to 23 radiating ribs and numerous fine, concentric lines. External color of left (upper) valves gray, brown, purple, orange, yellowish or white, often streaked , banded or some what variegated; color of right (lower) valves white or nearly so (in 75-100% of the specimens observed in each population) or similar to the left valve but usually lighter in color. Ribs evenly rounded or with flattened tops. Radial threads and cords present on auricles and on disc near auricles. Byssal notch in right valve with about 4 minute, erect teeth. Interior of valve s nacreous or white and exhibiting the exterior color near the margin (but not as prominently as in A. irradians s .s.) and sometimes, to a slight degree, over the whole inner surface. Muscle scars and pallial line faint or not discernible. Ratios of W/ L and H/L approximately 1.03 and .26 respectively for left valves and 1.02 and .32 for right valves. In Table 7 representative measurements are given for 6 specimens.
TABLE 7. Representative measurements of Aequipecten irradians concentricus
Types. Virtually all of Say's types which are still in existence are at the Academy of Natural Sciences, in Philadelphia. None of his original specimens of Pecten concentricus are in that institution, the Museum of Comparative Zoology, or the United States National Museum and it must be presumed that they are lost. In the interests of stability a neotype, corresponding as closely as possible to Say's original description and locality, is here selected (Plate 3, Figs. 5-8). It bears catalogue number 56295 and is in the collection of the Academy of Natural Sciences, Philadelphia. It was collected alive at Atlantic City, New Jersey by S. R. Morse, and is one of a lot of 4 specimens. This lot is described more fully
as Sample G in Table 3. Remarks. Inspection of the charts in Figures 1 to 5 indicates that Group II (irradians) an d Group III (concentricus) are quite dissimilar throughout most of their ranges but that they intergrade in the region from New Jersey to Maryland. Gutsell (1931) and Sastry (1963) have shown that significant differences in spawning behavior between the 2 forms also exist. The name A. concentricus is in wide use for Group III and it is desirable to maintain that name for this economically important subspecies if possible. By selection of a neotype from Atlantic City the name is fixed to an intermediate population which is morphologically closer to Group III than to Group II, and although this is not an ideal solution to the problem, it is the best that can be done. In terms of total rib count, the Atlantic Coast populations of A. i. concentricus differ somewhat from the Gulf Coast populations of that subspecies. Average rib counts for the 2 subgroups are 18.7 and 20.6 respectively, but since the range of variation of both subgroups overlap extensively (see Fig. 1) and no other differential characters have been found, it is considered unwise to attempt to differentiate them taxonomically. Range. New Jersey to South Carolina and Florida West Coast to eastern Texas. More precise limits are at present unknown. Geologic range: Pleistocene to Recent (Ball, 1898).» CLARKE JR., A. H. 1965. The scallop superspecies Aequipecten irradians (Lamarck). Malacologia, 2 (2): 161-188. [p. 178, 179]
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Aequipecten irradians concentricus (Say); A. H. Clarke Jr., 1965, The scallop superspecies Aequipecten irradians, plate 3, figures 5-12 (above); plate 4, figures 1-8 (below).
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