Nodipecten subnodosus (G. B. Sowerby I, 1835)
SOWERBY I, G. B. 1835. Characters and observations on new genera and species of Mollusca and Conchifera collected by Mr. Cuming. Proceedings of the Zoological Society of London, 3: 4-7, 49-51, 93-96, 109-110. [p. 109]
Pecten subnodosus Sow.; L. A. Reeve, 1852-1853, Monograph of the genus
Pecten, Conchyologia Iconica, plate 4, figure 20.
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«PECTEN SUBNODOSUS. Pect. testa subaequivalvi, aequilaterali, auriculis inaequalibus; striis radiantibus numerosissimis, radiisque decem, crassis, rotundatis, alternatim nodoso-vesicularibus vel subnodosis; intus plerumque purpureo signata: long. 5·25, lat. 2∙75, alt. 5· poll.
Variat α, colore rufo-fuscescente, striis albis, Hab. ad Sinum Callforniae. β, coloribus subvariegatis picta seu fusca, maculis albis utplurimum notata. Hab. ad Insulam Platae, Columbiae Occidentalis. γ, testa depressiore, colore aurantiaco nitente. Hab. ad Sinum Tehuantepec, Mexicanorum. Found in sandy mud and coral sand in from ten to seventeen fathoms.» GEORGE BRETTINHAM SOWERBY I, 1835
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«Node 10, marking the origin of the modern N. subnodosus lineage, is signaled by 1) a thickened shell, 2) stronger and more angular plicae in the first 10 mm of growth, 3) earlier appearance (at heights 6 mm) of commarginal frills in rib interspaces, and 4) a narrower umbonal angle. The left-valve rib pattern of N. subnodosus is N r Nc r N, a plesiomorphic state present in N. nodosus. J. T. Smith (1991a, p. 98) regarded N. subnodosus to be ‘‘directly descended from the Caribbean cognate N. nodosus or its immediate ancestor, N. collierensis.’’ J. T. Smith (1991a, p. 98) also noted that a population of N. subnodosus from Ángel de la Guarda Island in the Gulf of California (USNM 765008) has variable rib schemes that overlap the rib pattern of N. arthriticus. I concur with Smith, however, that these specimens have other features that place them in N. subnodosus, including the earlier appearance of more angular, stronger ribs in early ontogeny than is found in N. arthriticus.»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands. Journal of Paleontology, 81 (5): 929–950. [p. 934]
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Phylogeny of Lyropecten Conrad, 1862 and Nodipecten Dall,
1898; T. R. Waller, 2007, The evolutionary and geographic origins on the endemic Pectinidae of the Galapagos Islands, figure 3. |
«Remarks: Specimens from western Lower California and the Gulf of California to southern West Mexico are usually larger at maturity, lighter in color, and with 10 ribs on the right valve and 9 on the left, while those from central West Mexico (overlapping the above) to Peru are usually smaller, darker, and with 11 ribs on the right valve and 10 all the left. Conrad's Pecten intermedius was based on the northern "form"; he commented, "It differs from subnodosus ... in having much finer striae, numbering nearly double as many between each rib." The finer striae are actually found only on occasional specimens, and the features of the northern "form" mentioned above would not be of specific or infraspecific significance even if they were constant.
Variety β of Sowerby's Pecten magnificus was almost certainly a specimen of Nodipecten subnodosus; its type locality, La Plata Island, Ecuador, is the same, and only N. subnodosus has been subsequently recorded from that area. Apparently N. magnificus is restricted to the Galapagos Islands, while N. subnodosus has not been found there. Of this species Dall said, "There seems to be little reason for separating this form from the P. nodosus of the Antilles. Both vary through a strictly analogous series of mutations." (1898, p. 710.) A recent concurrence with that view was expressed by Dodge, who commented, "It seems to be an ecological and evolutionary form of nodosus and suggests a migration of that species in Miocene times by an ocean passage through what is now Central America." (1952, p. 172.) The important point in Dall's remarks is that the "series of mutations" by which the species vary are "strictly analogous"; an analogue, by definition, is not an object identical with another, and, although Nodipecten subnodosus is recognized as the eastern Pacific analogue of N. nodosus, there are important and easily seen differences between them. As for Dodge's opinion, even if conclusive evidence of migration could be shown, N. subnodosus is sufficiently restricted ecologically and stabilized morphologically to be regarded as a distinct species. Geographical range: Western Lower California: Scammon Lagoon to Cape San Lucas. Gulf of California to Negritos, Peru. Geochronological range: Pliocene, Pleistocene, Recent. Bathimetric range: Recorded from low tide to 60 fathoms. Ecological data: Found in shallow depressions in sand at low tide; in deeper water on rock, sand or mud bottoms, associated with red algae, nullipores, coralline and coral; vermetids, bryozoans and barnacles often commensal.» GRAU, G. 1959. Pectinidae of the eastern Pacific. Allan Hancock Pacific Expeditions, 23: i-viii, 1-308, 57 pls. University of Southern California Press. Los Angeles, California. [p. 131, 132]
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Nodipecten nodosus (Sowerby) 1835; G. Grau, 1959, Pectinidae of the eastern Pacific, plate 43.
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«RANGE: lower Pliocene to Recent.
REMARKS: Grant and Gale (1931, p. 179-182) united this species with Pecten nodosus (Linnaeus). However, the two may easily be separated by the fewer interribs (usually 3 or 4) of that species compared to 6 or 8 on Sowerby's species. Further, L. subnodosus is usually more inflated. A large specimen from loc. A 3591 has much less than the normal degree of inflation but still retains the greater number of interribs. Many of the specimens from loc. A 3521 are similarly less inflated, a condition that has not been noted in any of the recent specimens. In all, over 75 fossil specimens have been examined. The specimens from locs. A 3558 and A 3568 are much less inflated than the typical form, and, inasmuch as they are from the older beds, they may represent a new species, but as they are not well preserved one cannot be certain. Pecten subnodosus Sowerby of Hanna (1926, p. 474, pI. 25, fig. 6) seems to represent an undescribed species. The valve has very little convexity and appears to have only 2 or 3 interribs. A large right valve from loc. A 3547 has an altitude of 170.5 mm, a length of 174.3 mm, and a thickness (one valve) of 44 mm.» DURHAM, J. W. 1950. Megascopic paleontology and marine stratigraphy. In 1940 E. W. Scripps Cruise to the Gulf of California, Part II. Geological Society of America Memoir 43: 1-216, pls. 1-48. [p. 66]
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Lyropecten subnodosus (Sowerby); J. W. Durham, 1950, Megascopic paleontology and marine stratigraphy, plate 11, figure 1.
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