Acila (Truncacila) hokkaidoensis ( Nagao, 1932 )
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publication ID |
https://doi.org/ 10.4202/app.2008.0310 |
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persistent identifier |
https://treatment.plazi.org/id/497287A1-F62A-7B26-9FA8-F914FEB3F291 |
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treatment provided by |
Felipe |
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scientific name |
Acila (Truncacila) hokkaidoensis ( Nagao, 1932 ) |
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Acila (Truncacila) hokkaidoensis ( Nagao, 1932)
Fig. 4A View Fig .
1932 Nucula (Acila) hokkaidoensis sp. nov.; Nagao 1932: 28–30, pl. 5:
17, 18. 1936 Acila (Truncacila) hokkaidoensis (Nagao) ; Schenck 1936: 52. 1938 Nucula (Acila) hokkaidoensis Nagao ; Nagao and Otatume 1938:
37, pl. 1: 1. 1941 Acila (Truncacila) hokkaidoensis (Nagao) ; Nagao and Huzioka
1941: 118–119. 1975 Acila (Truncacila) hokkaidoensis (Nagao) ; Hayami 1975: 21. non 1958 Acila (Truncacila) hokkaidoensis (Nagao) ; Ichikawa and
Maeda 1958: 79–80, pl. 3: 9–11, 14. non 1962 Acila (Truncacila) hokkaidoensis (Nagao) ; Saito 1962: 59–60,
pl. 1: 1. non 1976 Acila (Truncacila) hokkaidoensis (Nagao) ; Tashiro 1976: pl.
1: 12–16. non 2007 Acila hokkaidoensis (Nagao) ; Tsujino and Maeda 2007: figs.
6C, D.
Material.— One specimen from the Omagari seep site, 27 specimens from the Yasukawa seep site (figured: UMUT MM 29531 ) .
Discussion.— Nagao (1932: 29) indicated that Acila hokkaidoensis is easily separable from other Recent and fossil species in Japan “in that the line, from which the radial ribs diverge downward, is placed much anteriorly to the median vertical”. This applies not only for the Japanese species but also for most species from the American side of the North Pacific, including the nine species of Truncacila reported by Weaver (1942) from the Cenozoic of Oregon and Washington, and the seven Cretaceous species of Truncacila described by Squires and Saul (2006) from British Columbia to Baja California. However, Squires and Saul (2006) noted that these North American Cretaceous species were from warm, shallow water sediments and that the deep−water species from the same area need critical evaluation. A specimen with a similar anterior line of divergence was figured as Acila (Truncacila) haidana Packard in Schenck, 1936 from the Redding Fm, Frazier Siltstone Member (Turonian) in northern California ( Squires and Saul 2006: fig. 15). The holotype of Acila (Truncacila) haidana figured by Squires and Saul (2006: figs. 13, 14, and 16) has the line of divergence in a central position. The specimen from the Californian Turonian Redding Formation might thus belong to Acila (Truncacila) hokkaidoensis .
Tsujino and Maeda (2007: fig. 6C, D) figured a specimen from the lowermost Campanian of the Upper Haborogawa Formation in west−central Hokkaido as A. (T.) hokkaidoensis which has the line from which the radial ribs diverge in a central position; this specimen most probably belongs to A. (T.) himenourensis Tashiro, 1985 (discussed below).
Stratigraphic and geographic range.—Turonian of California, USA (uncertain); Coniacian to Campanian of the Yezo Group, Japan.
| UMUT |
University Museum, University of Tokyo |
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