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Zoological Science
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Abstract
Seven (including one new) species of the polyplacophoran genus Ischnochiton (Ischnochitonidae) from the Pacific coast of Japan, namely, I. boninensis, I. comptus, I. manazuruensis, I. hakodadensis, I. hayamii sp. nov., I. paululus, and I. poppei, were investigated on the basis of DNA sequence analyses of COI, 16S rRNA, 18S rRNA, and 28S rRNA gene regions. For the latter four species, SEM observations were simultaneously carried out. A molecular phylogenetic tree based on the four gene regions for 18 chiton species indicated that the seven Japanese Ischnochiton species are polyphyletic and originated from two different clades. A haplotype network based on the COI gene region for the six Japanese Ischnochiton species, except I. hakodadensis, showed that the genetic distances among them were large. The SEM observations revealed that the denticles of the major lateral teeth in the seven Japanese Ischnochiton species were bicuspid, and an accessory process was only observed in the minor lateral teeth of I. hakodadensis. Ischnochiton hayamii sp. nov. cooccurs with I. boninensis, I. comptus, and I. manazuruensis at the two investigated localities, and was difficult to distinguish from other, similar species by naked eyes. However, these can be discriminated based on a combination of adult body size, girdle scales, and valve sculpturing in the lateral and central areas.
I deeply thank Akiya Hino and Ken'ich Kanazawa (both Kanagawa University) for their support during the present study, and Masaya Saito, Tsuyoshi Kobayashi (both Kanagawa University) and Hirokazu Abe (Tohoku University) for their help in collecting specimens. I would like to express my appreciation to Kazushige Tanabe (University of Tokyo) and Toshiyuki Yamaguchi (Kanagawa University) for their critical review of the first draft, Yasuhiro Ito (UMUT) for repository of the type and figured specimens, and Douglas J. Eernisse (University of California) for his review and suggestions. I also thank to editors and reviewers for useful comments to improve the manuscript.
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