Nipponopecten Masuda, 1962
MASUDA, K. 1962. Tertiary Pectinidae of Japan. Science Reports of the Tohoku University [2nd. Series - Geology], 33 (2): 117-238, pls. 18-27. [p. 194]
«Subgenus Nipponopecten Masuda, n. subgen.
Type-species: — Pecten akihoensis Matsumoto, 1930. Miocene Moniwa member of Hatatate formation of Miyagi Prefecture.
Geological distribution: — Early Miocene.
Diagnosis: — Shell moderate to large in size, moderately thick, compressed, suborbicular, subequilateral, subequivalve; exterior of right valve rather smooth, with fine concentric growth lines only in younger stage but tend to become numerous, rather faint, fine radial threads in adult; left valve with numerous, close-set, fine radial threads, intercalary threads and concentric growth lines; anterior auricle somewhat larger than posterior, with wide and shallow byssal notch, with concentric lines and faint radial threads; hinge with rather distinct but simple cardinal crura, shallow and wide resilial pit with distinct lateral ridges, without notch below resilial pit; interior surface smooth.
Remarks: — This new subgenus is represented by two Miocene species, that is, Placopecten (Nipponopecten) akihoensis (Matsumoto) and Placopecten (Nipponopecten) wakuyaensis Masuda. Placopecten s. s. differs from Nipponopecten in having numerous, fine radial threads extending from beak to ventral margin, striated inner margin and notch below resilial pit. This may be intermediate between Placopecten and Patinopecten.»
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Pecten (Pseudamusium) [sic] akihoënsis Saga (MS.), sp. nov.; H. Matsumoto, 1930, On the Marine Faunae of Three Fossil Zones of the Upper Miocene of Natori District, Province of Rikuzen, plate 40, figures 7, 8.
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KÔICHIRÔ MASUDA, 1962
Nipponopecten akihoensis (Saga in Matsumoto, 1930); T. Matsubara, I. Noro, Y. Matsuura & T. Irizuki, 2014, Miocene Mollusca from the Ichibu Formation on Nishinoshima Island, figures 7.5, 7.7a–7.7c.
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«Subtribe Fortipectinina Masuda, 1963
Genus Nipponopecten Masuda, 1962 Type species.— “Pecten akihoensis Matsumoto, 1930” [=Pecten (Pseudamusium) akihoensis Saga in Matsumoto, 1930] by original designation.
Discussion.— The systematic position of Nipponopecten Masuda, 1962 is controversial. It was originally proposed as a subgenus of the genus Placopecten Verrill, 1897 [“1899”] (type species: Pecten clintonius Say, 1824 by original designation). Subsequently, Masuda (1963) and Kafanov (1986a, b) considered it as a full genus in the subfamily Fortipectininae Masuda, 1963, as well as Mizuhopecten Masuda, 1963 (type species: Pecten yessoensis Jay, 1857), Fortipecten Yabe and Hatai, 1940 (type species: Pecten takahashii Yokoyama, 1930), Masudapecten Akiyama, 1962 (type species: Patinopecten (Masudapecten) masudai Akiyama, 1962), and Kotorapecten Masuda, 1962 (type species: Pecten kagamianus Yokoyama, 1923). On the other hand, Hertlein (1969) tentatively treated Nipponopecten as a junior synonym of Placopecten Verrill, 1897 [“1899”]. Recently, Kurihara (2010) referred Nipponopecten Masuda, 1962, to the subfamily Chlamydinae von Teppener, 1922, but left its tribal affiliation as incertae sedis.
As discussed by Waller (1993), the external microsculpture is an important character for suprageneric classification in the family Pectinidae. The validity of Waller’s (1993) classification is strongly supported by molecular phylogenetic analysis (e.g. Matsumoto and Hayami, 2000). The type species of the genus Nipponopecten, Pecten (Pseudamussium) akihoensis Saga in Matsumoto, 1930, may have shagreen microsculpture on the left valve (e.g. Sato, 1991; this study), which is characteristic of the tribe Chlamydinae von Teppener, 1922 (Waller, 1993). Therefore, it is not referred here to the genus Placopecten Verrill, 1897 [“1899”] in the subfamily Palliolinae Korobkov in Eberzin, 1960, but rather to the tribe Chlamydini von Teppener, 1922 in the subfamily Chlamydinae, along with Patinopecten Dall, 1898, Mizuhopecten Masuda, 1963, Fortipecten Yabe and Hatai, 1940, Masudapecten Akiyama, 1962, Kotorapecten Masuda, 1962, and Yabepecten Masuda, 1963. Based on their cardinal properties and evolutionary history (Masuda, 1963, 1986b; Kafanov, 1986a, b), I herein refer Patinopecten Dall, 1898 and Yabepecten Masuda, 1963 to the subtribe Patinopectinina Habe, 1977, and other Northwest Pacific Patinopecten-like genera other than Yabepecten to the subtribe Fortipectinina Masuda, 1963.» MATSUBARA, T., I. NORO, Y. MATSUURA & T. IRIZUKI. 2014. Miocene Mollusca from the Ichibu Formation on Nishinoshima Island, Oki Islands, Southwest Japan. Paleontological Research, 18 (1): 6-32, figs. 1-11. [p. 19]
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