Chlamys cosibensis (Yokoyama, 1911)
YOKOYAMA, M. 1911. Pectens from the Koshiba Neogene. Journal of the Geological Society of Tokyo, 18 (208): 1-5, pl. 1. [p. 4, pl. 1, figs. 3, 4]
1911 Pecten cosibensis Yokoyama, 1911
1925 Pecten turpiculus Yokoyama, 1925
1926 Pecten heteroglyptus Yokoyama, 1926
1934 Pecten swiftii piltukensis Khomenko, 1934
1970 Chlamys (Swiftopecten) leohertleini MacNeil, 1970
1925 Pecten turpiculus Yokoyama, 1925
1926 Pecten heteroglyptus Yokoyama, 1926
1934 Pecten swiftii piltukensis Khomenko, 1934
1970 Chlamys (Swiftopecten) leohertleini MacNeil, 1970
M. Yokoyama, 1911, plate 1.
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«There are two specimens which I consider as belonging to this species. The one is a right valve (fig. 3) about 56 millim. hight and 12 millim. deep, suborbicular in shape and tolerably convex with unequal, rounded, straight, radiating ribs more or less in bundles separated by deep valleys which are also provided with radiating riblets. The surface is marked with few unequally deep concentric furrows situated at unequal distances from another. The ears are unequal with strong interrupted ribs. Byssul notch distinct.
The other valve which lacks the umbonal portion is much flatter and with only a single deep concentric groove. It may be a left valve. This species show some relationships to Pecten Ruschenbergi Tryon (Chemnitz Conchylien-Cabinet Vol. VII, p. 275. pl. 72 fig. 4) from Bay of Mascat.» MATAJIRO YOKOYAMA, 1911 |
«Hertlein and Grant (1972) and Waller (1991) included Pecten cosibensis Yokoyama, 1911 in the genus Swiftopecten. However, Masuda (1972) argued that Chlamys cosibensis should not be allocated to Swiftopecten on the grounds that Swiftopecten can be distinguished from C. cosibensis by its large, higher, posteriorly contorted shell, smaller apical angle, triangular large anterior auricle and nearly flat left valve in the younger stage. In my opinion, C. cosibensis should not be assigned to the genus Swiftopecten due to differences in the deep byssal notch, the small maximum shell height, the small number of fine riblets and the lesser unevenness of the ledges. I believe that prominent ledges have evolved independently in Swiftopecten and Nanaochlamys species and in Chlamys cosibensis, therefore C. cosibensis should be excluded from Swiftopecten.»
YOSHIMURA, T. 2017. A New Pliocene Species of Swiftopecten (Bivalvia: Pectinidae) from the Zukawa Formation in Toyama Prefecture, Central Japan. Paleontological Research, 21 (3): 293-303, figs. 1-6. [p. 295, 296]
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«Recent discussions of the phylogeny of Swiftopecten and related pectinids by Hertlein and Grant (1972) and Masuda (1972, 1973, 1986) suggest to this writer how five genera (Chlamys, Manupecten, Nanaochlamys, Semipallium, and Swiftopecten can be related in a phylogeny that began in the early Miocene in the warm waters of the low-latitude western Pacific (Fig. 10). The stem group is Chlamys, sensu lata, in which the ribbing consists of fine costae that multiply on the right valve mainly through branching and on the left valve mainly through intercalation, much as in modern Chlamys farreri. At this stage shagreen microsculpture was present but was limited in extent on each valve. The shared derived features that evolved at point A in Figure 10 were the extension of shagreen microsculpture throughout ontogeny after the prismatic stage, a narrowing of the umbonal angle with a correlative increase in auricle height and decrease in depth of byssal notch, and, most significantly, larger radial ribs that formed over the pattern of finer ribbing present in Chlamys. It is also possible that at this point, incipient ledging originated, because this feature is present in some members of the genus Semipallium (e.g., Semipallium tigris (Lamarck, 1819), USNM 321733 and USNM 764007) .
Fig. 10. Phylogenetic relationships of Swiftopecten swifti to three living genera and one extinct genus. Letters refer to derived characters described in text.
At point B in Figure 10 the important derived feature that unites the extinct genus Nanaochlamys Hatai & Masuda, 1953, and living Swiftopecten is the reduction in number of secondary first-order ribs and their arrangement in a specific pattern, with five major ribs on the left valve and four major ribs on the right. This pattern is clearly present at least in the early ontogeny of Nanaochlamys (see Plate 7 in Masuda, 1986) and persists throughout ontogeny in Swiftopecten, although the earliest known species in Swiftopecten, S. cosibensis (Yokoyama, 1928) from the upper Lower Miocene of Japan (Sato, 1982), shows instability in the pattern (see Plates 8 and 9 in Masuda, 1973). Also at point B (Fig. 10), larger scale ledging originated, with ledging amplitude greater on the left valve than on the right . Ledging may occur only once in the early ontogeny of Nanaochlamys, leading to an apparent flattening of the early growth of the left valve,which was misread by MacNeil (1967) as a possible indication of relationship with the genus Pecten. At point C (Fig. 10), secondary flaring of the shell and splitting of the firstorder plicae characterize Nanacochlamys. At point D, frequent ledging during ontogeny characterizes Swiftopecten (in which I include Chlamys cosibensis, in agreement with Hertlein and Grant (1972) but not with Masuda (1973)). It seem s likely that the extens ive foliated calcite reentry present in Swiftopecten swifti originated at point D, in association with the decline of water temperatures that signaled the appearance of S. cosibensis (Masuda, 1986), although it is also possible that this feature originated at point B and is shared with Nanaochlamys. (I have not examined specimens of Nanaochlamys for this feature, nor have other authors described its presence.) It can be seen from this phylogeny that Manupecten resembles Swiftopecten because these taxa share primitive characters that are also present in Semipallium. The principle unique feature of Manupecten which sets it apart from Semipallium (point E in Fig. 10) is the consistent presence in the former of enclosed pustulose scales along the dorsal margins of the auricles (PI. 2, Figs. 11, 12).
In summary, this phylogeny suggests that the closest living species to Swiftopecten swifti are to be found in the genus Semipallium, but these Semipallium species diverged from the Swiftopecten clade before the end of the early Miocene, at least 20 million years ago. Manupecten pesfelis is probably a mor e distant relative, and members of the genus Chlamys, such as C. farreri, even mor e distant.» 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, pls. 1-8. [p. 24-27]
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Nanaochlamys notoensis (Yokoyama), figures 1-5; Nanaochlamys notoensis otutumiensis (Nomura and Hatai), figure 6; Swiftopecten swiftii (Bernardi), figure 7; K. Masuda, 1986, Notes on the origin and migration of Cenozoic pectinids in the Northern Pacific, plate 7.
Chlamys cosibensis (Yokohama); K. Masuda, 1973, Chlamys cosibensis (Yokohama) of the Northern Pacific, plates 8, 9.
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«Several specimens agree very well with the descriptions of this species given by Yokoyama (1911) and Masuda (1973). This species can be distinguished by its medium-sized shell, suborbicular outline, apical angle of about 90 degrees and surface ornamentation of about 20 subequal radial ribs. This fossil is widely distributed in the northern Pacific region: in Miocene and Pliocene formations of the Japanese islands and Cheju Island, Korea, and in Pliocene formations of Sakhalin, Kuril, Kamchatka and Alaska (Zhidkova et aI., 1972; Masuda, 1973, 1983, 1986a, b; Sinelnikova, 1975, Marincovich, 1983).»
O'HARA, S. & N. NEMOTO. 1988. Pectinids from the Taga Group of the Joban Coalfield. Saito Ho-on Kai Special Publication, Professor Tamio Kotaka Commemorative Volume: 481-496, pls. 1-4. [p. 489]
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Chlamys cosibensis (Yokoyama, 1911); S. O'Hara & N. Nemoto, 1988, Pectinids from the Taga Group of the Joban Coalfield, plate 3, figures 2, 3.
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«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.»
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. 401]
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«Comparison and Affinity :-- Chlamys (Swiftopecten) swiftii (BERNARDI) is distinguised from the present one by its large, posteriorly contorted shell which is much higher than long, smaller apical angle, triangular anterior auricle, rather simple cardinal crura and rather flat hinge plate sculptured with fine striae parallel to the hinge line, and nearly flat left valve in young shell. Chlamys wattsi (ARNOLD) (ARNOLD, 1906, from the Pliocene of Fresno County and Chlamys wattsi morani (ARNOLD) (ARNOLD, 1906) from the Pliocene of Monterey County, both in California. resemble the present species: the former differs from cosibensis by its right valve having convexity nearly equal with the left valve, radial ribs, less prominent byssal notch and obsolete posterior auricle, and from the latter by its radial ribs with five to seven, strong, squarish, elevated radial threads, slightly developed byssal notch, short posterior auricle and less distinct concentric constrictions. Chlamys etchegoini
(ANDERSON) (NOMLAND, 1917) from the Pliocene of Fresno County, California. resembles this species, but differs by the radial ribs and the obsolete posterior auricle. Remarks :-- This species which is characterized as above described are from the localities nientioned below.
Described specimens :— River cliff of the Chikagawa stream, about 200 m. from the sea shore at Chikagawa, Tanabumachi, Shimokita-gun, Aomori Prefecture. Silty fine-grained sandstone of the Hamada formation (Pliocene). DGS, Reg. No. 3686. IGPS, coil. cat. no. 72556. Occurrence :— Aoso, Nanakita and Utsuno formations in Miyagi Prefecture, Ginzan formation in Yamagata Prefecture, Suenomatsuyama formation in lwate Prefecture, Shigarami formation in Nagano Prefecture, Sawane and Shiraiwa formations in Niigata Prefecture, Sasaoka formation in Akita Prefecture, Koshiba formation in Kanagawa Prefecture, Hamada and Daishaka formations in Aomori Prefecture and Setana formation in Hokkaido: Late Early Miocene to Pliocene in age.» MASUDA,
K. 1959. On the Miocene Pectinidae from the Environs of Sendai; Part
15, Pecten cosibensis Yokoyama and its related species. Transactions and
Proceedings of the Palaeontological Society of Japan [N. S.], 35:
121-132, pI. 13. [p. 123-125]
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Chlamys cosibensis (Yokoyama) 1911; K. Masuda, 1559, Pecten cosibensis Yokoyama and its related species, plate 13, figures 1-9.
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