Mizuhopecten yessoensis (Jay, 1857)
JAY, J. C. 1857. Report on the shells collected by the Japan Expedition, under the Command of the Commodore, M.C. Perry, U.S.N., together with a list of Japanese Shells. In “Narrative of the Expedition of an American Squadron to the China Seas and Japan, performed in the years 1852, 1853, and 1854 under the command of Commodore M. C. Perry, United States Navy, by the order of the Government of the United States. Vol. II with illustrations. Washington, D. C.: 291-297 [p. 293, pl. 3, figs. 3-4; pl. 4, figs. 1-2]
1857 Pecten yessoensis Jay, 1857
1861 Pecten brandtii Schrenk, 1861
1861 Pecten brandtii Schrenk, 1861
J. C. Jay, 1857, plates 3, 4.
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«Testa orbiculari, inaequivalvi, valva sinistra plano convexa, aequilaterali, costis triginta convexo planis, sublente tenuissime et criberrime concentrica striata, valva dextra convexiore costis duabus et viginti rotundatis, elevatiusculis, interstitiis latiusculis, auriculis valvae, sinistra aequalibus, dextra inaequalibus, antica subtus ernarginata.
Shell orbicular, inequivalve, left valve flatly convex, equilateral, with thirty convexly flattened ribs, very broadly and closely concentrically striated, right valve more convex, with twenty-two ribs, rounded, rather raised, interstices rather broad, ears of the left valve equal, of the right unequal, the front one being emarginated below. Habitat, Hakodadi. This shell grows to a very large size. One in the collection measures seven by eight inches. The right valve is used by the natives as a scoop. Since the above was written the author has visited the collections of the British Museum and of Mr. H. Cuming, and also those in the museum at Leyden, which were brought from Japan by Mr. Sieboldt, and did not see this shell.» JOHN CLARKSON JAY, 1857
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«The genus Mizuhopecten known from the Tertiary formations in the Japanese Islands is very abundant specifically and individually, but there are only two species, M. tokyoensis (Tokunaga) and M. yessoensis (Jay), known in the Pleistocene and only one species, M. yessoensis, from the Recent seas of Northern Japan. And it seems probable that the majority of the Patinopecten species recorded from Sakhalin and Kamchatka should be allocated to the genus Mizuhopecten, and that true Patinopecten does not occur in the Western Pacific. Therefore, it is evident that the appearance of Mizuhopecten warreni Masuda (1971 A) in the Late Miocene Montesano Formation of Washington and Mizuhopecten mollerensis (MacNeil, 1967) in the Late to Middle Miocene Unga Conglomerate of Alaska, both resulted from eastward migration from the Western Pacific region.
As already noticed by the writer (Masuda, 1971 A), from the paleontological data it can be concluded that Mizuhopecten might have been originally a warm water inhabitant in the Late Oligocene to Early Miocene in the Japanese Islands. Even though changes in marine environmental conditions from the Oligocene to Recent have greatly changed the generic composition of marine faunas, Mizuhopecten evidently became adapted to different environmental conditions. However, a result of gradually changing environmental conditions only Mizuhopecten yessoensis (Jay) survived to the Recent while but other Mizuhopecten species became extinct.» MASUDA, K. 1986. Notes on the origin and migration of Cenozoic pectinids in the Northern Pacific. Paleontological Society ofJapan, Special Papers, 29: 95-110, pls. 7-10. In T. Kotaka (Ed.), Japanesse Cenozoic mollusca: their origin and migration, vii, 255 p., pls. 1-21. [p. 96]
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Mizuhopecten yessoensis (Jay); K. Masuda, 1986, Notes on the origin and migration of Cenozoic pectinids in the Northern Pacific, plate 9, figure 1.
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«Holotype: – Unknown.
Remarks: – Patinopecten caurinus (Gould) (Arnold, 1906, p. 101, pI. 38, figs. 1, 1a-b, pI. 39, figs. 1, 2), fossil and Recent of California, is distinguishable from the present one by its compressed shell, strongly flat-topped, squarish radial ribs in the right valve and the rather prominent byssal notch. Numerous specimens of this species from various localities of Japan show variable characters, that is to say, the radial ribs of the fossil right valve from the Setana formation at Kaigara-zawa, Kuromatsunai, Hokkaido and from the Dainenji formation at Kanodomon, Sendai City, Miyagi Prefecture, are generally low and flatly round-topped, and those of the Recent specimens from the Mutsu Bay at Asamushi, Aomori Prefecture, are also generally low, flatly round-topped and rarely narrower than their interspaces in breadth. While the radial ribs of the fossil specimens from the Setana formation at Maruyama, Kita-Hiyama-machi, Hokkaido, from the Sawane formation, Niigata Prefecture and from the Shibikawa formation at Oga Peninsula, Akita Prefecture, are generally round-topped, broader than their interspaces, more elevated and distinct when compared with those from Kaigara-zawa, Kano-domon or Asamushi. The left valves from the Setana, Sawane and Shibikawa formations are usually nearly flat or very slightly inflated, or sometimes slightly concaved, inwards, though they are slightly inflated in very young shell (Prodissoconch), while those of the Recent specimens from Asamushi, Muroran, etc. are generally slight- or moderately inflated and only a little less convex than the right valve. Moreover, the specimens from Asam'Ushi are usually rather thinner than those from the other localities. According to Tanaka (1906) who studied the morphology of yessoensis, the shells living in the calm sea are generally rather large in size, the convexity of the right valve is rather small and the left valve is rather inflated, but those living elsewhere are generally thick, the convexity of the right valve is rather large and the left valve is nearly flat. This data may serve to interpret the paleoecological conditions of the fossil yessoensis. The number of radial ribs also show a considerable variation. According to Kinoshita (1937) the number of radial ribs of the right valve from Hokkaido varies from 15 to 32, 21 to 24 being the frequent number, and that of the left valve varies from 13 to 31 and the most frequent number is 20. The number of radial ribs of the specimens from the Setana formation varies from 21 to 28, 22 to 24 being the frequent number, those from the Sawane formation varies from 21 to 29 and 22 to 26 are frequent, and those from the Shibikawa formation varies from 17 to 26, 22 to 22 being the frequent number. Kinoshita (1937) has concluded that the variation of the number of radial ribs is not due to the ecological conditions of the sea but may be due to the internal factors of the animal itself. This species is common in Northern Japan, but sometimes it lives in the areas influenced by the warm water current, but annually or seasonally fed with the cold crurrent. Therefore, it is evident that it is more or less eurythermal and it seems to prefer a rather shallow (about 18 to 120 m.) clean sea bottom consisting of rather coarse-grained sediments influenced by rather strong current. Type locality: – Hakodate, Hokkaido. Recent. Distribution: – Dainenji formation, Miyagi Prefecture; Koshiba formation, Kanagawa Prefecture; Sawane, Nishiyama and Haizume formations, Niigata Prefecture; Shibikawa and Sasaoka formations, Akita Prefecture; Setana, Shishinai and Kushiro formations, Hokkaido; Living in the Pacific (35°-45°N.) and the Japan Sea (36°-46°N.): Early Pliocene to Recent. Occurrence: – Abundant in the medium-grained sandstone, common in the fine-grained sandstone and few in the granule conglomerate of the Setana formation; abundant in the very coarse-grained sandstone of the Sawane formation; abundant in the coarse-grained sandstone of the Shibikawa formation; few in the very fine-grained sandstone of the Dainenji forrnation.» MASUDA, K. 1962. Tertiary Pectinidae of Japan. The Science Reports of the Tōhoku University [2nd. Series -Geology], 33 (2): 117-238, pls. 18-27. [p. 213, 214]
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Patinopecten yessoensis yessoensis (Jay); K. Masuda, 1962, Tertiary Pectinidae of Japan, plate 26, figures 5, 6.
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