Nodipecten arnoldi (Aguerrevere, 1925)
AGUERREVERE, P. I. 1925. Description of a new Pecten from Venezuela, S.A. Bulletin of the Southern California Academy of Sciences, 24 (2): 51-53, pl. 5. [p. 51, pl. 5]
1886 Pecten gigas Karsten, 1886 [nomen nudum]
1925 Pecten (Lyropecten) arnoldi Aguerrevere, 1925
1925 Pecten (Lyropecten) arnoldi Aguerrevere, 1925
P. I. Aguerrevere, 1925, plate 5.
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«Description: Shell slightly broader than high, subequilateral, subequivalve, medium thickness, submargins with fine, close, undulating growth lines; base rounded; sides slightly curving out near the ends. Right valve slightly nodose in the first stages of growth; with nine or ten broad flat ribs with three or four flat riblets; interspaces slightly narrower than the ribs with one prominent riblet in the center and a minor one on either side, the interspacial riblets being much more prominent than those on the ribs; the whole surface is covered with undulating concentric lines of growth which almost obliterate all other sculpture near the periphery. Anterior ear less than one and one tenth times as large as the posterior, with four radiating riblets; the whole ear is covered with fine, close, growth lines becoming stronger towards the end; byssal notch not very prominent; byssal area with concentric area of growth only. Posterior ear squarish, somewhat rounded in the rear, with very faint or no riblets, but with a stronger concentric sculpture than the anterior. Umbo rather sharply pointed ending at the hinge line. Left valve resembling the right except that it is slightly more nodose, the ribs are narrower, and the interspaces are wider in proportion. The left valve is slightly less arched than the right.
Dimensions of the type: altitude 210 mm.; longitude 218 mm.; hinge line 115 mm.; diameter 95 mm. Pecten nodosus Linnaeus of Margarita Island seems to be a descendant of Pecten arnoldi. It retains the shape and the number of ribs, and in a general way the sculpture of P. arnoldi but it is much more nodose. The riblets of P. nodosus are more abundant and more prominent than on P. arnoldi; however, the riblets in the interspaces are still only three or four and are more prominent than those on the ribs. The whole shell of P. nodosus has very fine and inconspicuous lines of growth while P. arnoldi has very conspicuous growth lines. The anterior ear of P. nodosus still keeps the ribs found in P. arnoldi, but it has besides a number of less prominent ones. The byssal area and the posterior ear of P. nodosus have both radiating riblets and concentric lines, the former being more prominent than the latter; while in P. arnoldi the riblets are very faint or do not exist at all. Pecten subnodosus Sowerby of the Pacific Coast resembles P. arnoldi in the general shape of the shell and the number of ribs; however, the sculpture of P. subnodosus consists of fine numerous riblets equally distributed on the ribs and the interspaces, with few, widely separated lines of growth. The byssal hinge and the anterior ear of P. subnodosus are equally covered with many minor riblets; while P. arnoldi has only concentric growth lines on the byssal area and four riblets with concentric lines on the anterior ear. The posterior ear of P. subnodosus has radiating riblets; that of P. arnoldi has concentric sculpture. In its youth, P. subnodosus resembles more P. arnoldi than in its maturity; the interspacial riblets are then more pronounced than those on the ribs; the anterior ear has only four radiating riblets with concentric sculpture and the byssal area has only concentric sculpture. The type specimen of Pecten arnoldi was found 1 and ¾ miles east of the Castle of Cumana, State of Sucre, Venezuela, S. A. This, the largest known species of Pecten, is very appropriately named in honor of Ralph Arnold, in recognition of his contributions to our knowledge of the Pecten group, and to the stratigraphy of the Tertiary in California and Venezuela. Horizon: probably Miocene.» PEDRO IGNACIO AGUERREVERE, 1925
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«Holotype.— LSJU 364, a large two-valved adult measuring 21 cm high, 21.8 cm long.
Type locality. State of Sucre, Venezuela, Araya Peninsula, 1.75 mi east of the Castle of Cumana. Named in honor of Ralph Arnold for his extensive work with Pectens. Aguerrevere (1925) considered it "probably Miocene;" Weisbord (1964) referred the unit to the Playa Grande Formation, Catia Member, "*** tentatively, Pliocene in age." One lot of specimens labelled "topotypes" comes from "the Cumana beds" (USGS 18408). Cumana Formation, upper Pliocene (Hunter, 1978). Description.— Valves equally convex, height equals length; beaks project slightly, equally beyond hinge line. Auricles large, with heavy growth lines; anterior auricle with strong radial costae. Byssal notch moderately deep. Hinge line straight, about half shell length. Umbonal angle 95-110°, varying with shell convexity. Right valves have 9-10 evenly spaced, flat-topped rectangular ribs. Left valves with 8-9 ribs; juveniles to young adults 10 cm high have nodes on alternate ribs in a pattern described as N r Nc r N. Nodes may be incipient or prominent and flanged; none develop in gerontic growth stages. Fine macrosculpture coarse in juveniles to young adults, obsolete in large individuals that have prominent undulating growth lines (pl. 11, fig. 3; pl. 13, fig. 2). Right-valve ribs have 4-5 fine costae, interspaces with 1-3 midriblets; the central interspaces have fewer radials than later interspaces have. Variability.— Rib profiles are high and rounded in juveniles, low and rectangular in adults. Ribs and fine macrosculpture become obsolete in gerontic individuals. Juveniles may have one more rib than adults. Left valves have alternating key ribs, and four or more generations of nodes, but some specimens (for example, the holotype) do not. Comparative notes.— Nodipecten arnoldi is common in Neogene marine collections from the Venezuelan Coast Ranges. Its occurrence in the field with Lyropecten colinensis, s.s. and Nodipecten collierensis has not been documented by careful biostratigraphic work, so the three species have been confused in museum collections. Lyropecten colinensis s.s. has more ribs, 11-13, and a lyropectinid left-valve node scheme of N 2r Nc 2r N, but its fine macrosculpture and flanged nodes are similar to those of N. arnoldi. Nodipecten collierensis, N. pittieri, and N. arnoldi have the same number of ribs, 9-10, and overlapping morphologic characters. They differ in rib profiles and fine sculpture. The profile of Nodipecten pittieri is flatter than in the other two species, its dimensions longer than high; N. collierensis and N. arnoldi are equally convex and have a lower umbonal angle than N. pittieri. Phylogenetic affinities.— Nodipecten arnoldi belongs in the N. nodosus stock with other species having a leftvalve node scheme of N r Nc r N. It is closest to N. collierensis and may be a gigantic-size, tropical, lagoonal descendant of it. Juvenile valves of the two are hard to distinguish.» SMITH, J. T. 1991. Cenozoic giant pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species. United States Geological Survey Professional Paper, 1391: v + 1-155, figs. 1-18, pls. 1-38. [p. 87]
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Nodipecten arnoldi
(Aguerrevere, 1925); J. T. Smith, 1991, Cenozoic giant pectinids from California and the Tertiary Caribbean Province, plate 11, figures 3, 4 (abobe); plate 13, figures 2, 3 (below). |