Swiftopecten swiftii (Bernardi, 1858)
BERNARDI, A. C. 1858. Description d'spèces nouvelles. Journal de Conchyliologie [2e Série], 7 [3]: 90-94, pls. 1, 2 [p. 90, pl. 1, fig. 1; pl. 2, fig. 1]
1858 Pecten swiftii Bernardi, 1858
1920 Pecten (Chlamys) kindlei Dall, 1920
1967 Chlamys (Swiftopecten) donmilleri MacNeil, 1967
1920 Pecten (Chlamys) kindlei Dall, 1920
1967 Chlamys (Swiftopecten) donmilleri MacNeil, 1967
A. C. Bernardi, 1858, plates 1, 2.
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«Testa maxima, utrinque convexa, solidiuscula, nitida, elongata, valva superiore costis nodosis, majoribus 5, munita; nodis distantibus concentrice dispositis; intersliis longitudinaliter radiatis minutissime granulais, costis concentricus 5 gradatim dispositis; valva inferiore vix nodosa, regulariter radiatim sulcata; auriculis valde inaequilateralibus; supra nodosis, infra sulcatis.
Long. 105 mill. Larg. 90 ─ Coquille grande, convexe, assez solide, allongée, valve supérieure portant cinq grosses côtes, noueuses; nodosités éloignées, disposées sur des lignes concentriques au sommet; interstices striés longitudinalement, finement granuleux, sillonnés régulièrement et en long; auricules inégales, noueuses en dessus, sillonnées en dessous. Cette magnifique espèce appartient à la section des Pecten corallinus, pes-felis, etc. On compte en dessus 5 grosses côtes noueuses, à interstices radiés longitudinalement et finement granulés. La valve inférieure est à peine noueuse et régulièrement sillonnée. La coloration de la valve supérieure est rougeâtre, elle passe au lilas vers les crochets; la valve inférieure est blanche, teintée çà et là de rose. Intérieur blanc avec quelques reflets jaunâtres. Hab. la baie Nicolas, dans la Manche de Tartarie. (Collection du Journal). Observ. Ce beau peigne, que nous dédions à M. Swift, amateur zélé de Saint-Thomas, provient du voyage de la Sibylle. ─ Nous n'en connaissons que deux exemplaires: ils ont été péchés à la ligne.» A. C. BERNARDI, 1858
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«Masuda (1960) interpreted the extant north Pacific pectinid Swiftopecten swiftii as a direct descendant of N. notoensis because of the similarity of shell morphology in younger stages and the evidence of the fossil record (Figure 7A). According to him, the former is similar to the latter in both form and sculpture, and the latter is restricted to the early Miocene, when the former appeared. On the other hand, Sato (1982) briefly noted that Swiftopecten is not a direct descendant of Nanaochlamys, because N. notoensis otutumensis, a chronological subspecies of N. notoensis, cooccurs with S. swiftii in the middle Miocene Otsutumi Formation in Miyagi Prefecture, northeast Honshu. More recently, Waller (1991) proposed a similar view that Nanaochlamys and Swiftopecten independently evolved from a common ancestor, forming a single clade (Figure 7B). According to him, this clade is defined by sharing the following synapomorphies; reduction in the number of secondary first-order ribs and their arrangement in a specific pattern, and development of the larger scale ledging, with ledging amplitude greater on the left valve than on the right. The apomorphic features observed in Nanaochlamys are secondary flaring of the shell and splitting of the firstorder plicae, whereas in Swiftopecten frequent ledging during ontogeny is apomorphic.
S. swiftii and N. notoensis share similar shell features such as the shagreen microsculpture throughout ontogeny and the prominent primary radial ribs, numbering five on the left valve and six on the right one. However, these two species are distinguished by the differences in the allometric change of the umbonal angle versus shell height (Figure 5). Interestingly, the mode of ribbing on the left and right valves in the juvenile stage of N. notoensis is fairly similar to that in the adult stage of S. swiftii. This fact suggests to us a possibility that the latter species arose from the former species by neoteny. If neoteny actually occurred, the allometric trend of shell convexity in S. swiftii should resemble that in the early stage of N. notoensis. However, such a phenomenon is not observed in the two species, and the allometric trend of S. swiftii resembles that in the later stage of N. notoensis instead of the early stage. This fact strongly supports Waller’s (1991) opinion in which the two species are regarded as constituting sister groups.» HAYASHIDA, N. & K. TANABE. 2006. The mode of life and taxonomic relationship of a Japanese Miocene pectinid bivalve Nanaochlamys notoensis. Paleontological Research, 10 (1): 1-10, figs. 1-7. [p. 8, 9]
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Figure 7. Phylogenetic relationships of Nanaochlamys and
related genera and/or species postulated by Masuda (1960) (A) and Waller (1991) (B). |
«The present species is characterized by its large and thick, posteriorly contorted shell which forms an angle of about 70° at apex and is much higher than long, four prominent round-topped radial ribs with several, fine radial threads, two subordinate radial ribs near submargins, fine intercalary threads. rather conspicuous concentric constrictions, very large triangular anterior auricle and flat hinge plate in the right valve. The left valve is characterized by its five prominent, round-topped radial ribs which are usually nodose and by its young shell which is nearly flat or rarely a little concave upwards.
By the re-examination of the type specimen (U.S. Natl. Mus., No. 499058) and numerous topotype specimens, it is considered that Pecten (Chlamys) kindlei DALL is a synonym of swiftii, because the convexity of the valves, low radial ribs and concentric constrictions observed in kindlei are quite similar with those of swiftii. Similarly the hypotype specimen (U.S. Natl. Mus., No. 164842) and the specimens labelled as parmeleei (Dept. Geol., Stanford Univ., No. 4838) from the "Wildcat" Formation in the vicinity of Crescent City, Northern California, are synonyms of swiftii. Chlamys (Swiftopecten) donmilleri was described by MACNEIL (1967) from the Miocene Yakataga Formation, Alaska, based upon rubber casts. The morphological characters of the type specimens (U.S. Natl. Mus., No. 644882, 644883, 644884) as observed by the writer coincide with those of Swiftopecten swiftii, therefore, MACNEIL's donmilleri is a synonym of Swiftopecten swiftii. But Chlamys (Swiftopecten) cf. donmilleri described by MACNEIL (1967) from the Miocene Unga Conglomerate, Alaska Peninsula can not be identified with swiftii but with Chlamys cosibensis (YOKOYAMA) which is known from the Miocene to Pliocene formations in Japan. For the Chlamys cosibensis group another paper is expected to be written. Swiftopecten swiftii resembles Chlamys cosibensis (YOKOYAMA) and has been confused with it (MASUDA, 1959b). Also Chlamys etchegoini (ANDERSON), Chlamys nutteri (ARNOLD), Chlamys wattsi (ARNOLD) and Chlamys wattsi morani (ARNOLD) described from the Pliocene deposits of California resemble swiftii, which can be distinguished from those species and cosibensis by its large, higher, posteriorly contorted shell, smaller apical angle, triangular large anterior auricle and nearly flat left valve in younger stage. Type locality :— Northern Japan. Recent. Geographical distribution :— Living in Northern Japan, Sea of Okhotsk and along East Korea. Geological distribution :— Middle Miocene to Recent in Japan, Pliocene to Recent in Sakhalin and Kamchatka, and Middle (?) to Late Miocene to Middle Pleistocene along the West Coast of North America.» MASUDA,
K. 1972. Swiftopecten of the Nothern Pacific. Transactions and
Proceedings of the Palaeontological Society of Japan [N. S.], 87:
395-408, pls. 48, 49. [p. 400, 401]
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Swiftopecten swiftii (Bernardi, 1858); K. Masuda, 1972, Swiftopecten of the Nothern Pacific, plate 48, figures 1-5; plate 49, figures 1-5.
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