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Morphological characteristics and taxonomical problems of the genus Parasesarma De Man, 1895 (Crustacea: Decapoda: Brachyura: Sesarmidae) from the Ryukyu Archipelago, Japan

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  • 琉球列島のカクベンケイガニ属 (甲殻亜門: 十脚目: 短尾下目: ベンケイガニ科) 6 種の形態的特徴と分類学的諸問題


Six species of terrestrial sesarmid crabs of the genus Parasesarma De Man, 1895, viz. P. dumacense (Rathbun, 1914), P. lepidum (Tweedie, 1950), P. leptosoma (Hilgendorf, 1869), P. liho Koller, Liu & Schubart, 2010, P. pictum (De Haan, 1835), and P. tripectinis (Shen, 1940) were collected from the Ryukyu Archipelago, Japan, of which P. dumacense, P. lepidum and P. liho represent new records for the Japanese fauna. Notes on their morphological features, colorations, ecological aspects, and distributions in the Ryukyu Archipelago are provided. The identification of P. dumacense in the present study is provisional, as the original descripton of the female holotype of P. dumacense is insufficient to confirm the identification of the Ryukyuan specimens as male characters are most important to identify the species. Rahayu & Ng (2010) redescribed P. dumacense, but the present study indicates that Rahayu & Ng’s (2010) “P. dumacense” may contain more than two species (Fig. 4). Furthermore, Parasesarma kuekenthali is morphologically very close to P. dumacense. Further taxonomic study is necessary to clarify the systematic status of P. dumacense, P. kuekenthali, and the species studied by the present study and Rahayu & Ng (2010). It has been considered that P. lepidum is distinguished from allied P. palauense (Takeda, 1972) by the fewer number of granules on the upper surface of the movable finger of male chela (17–18 in P. lepidum vs. 19 in P. palauense). Our additional material of P. lepidum expands the range of the number of the granules to 20, which now overlaps with that of P. palauense. Reappraisal of the identity of P. palauense is necessary. Taxonomic problems and distinguishable characters of the other four Parasesarma species are also discussed in detail. Controversial distributional records of P. affine (De Haan, 1837) from the Ryukyu Archipelago are also discussed.

琉球列島において採集されたカクベンケイガニ属Parasesarmaの6種 [ヨコスジベンケイガニ (新称) P. dumacense (Rathbun, 1914), ツメナガベンケイガニ (新称) P. lepidum (Tweedie, 1950), キノボリベンケイガニP. leptosoma (Hilgendorf, 1869), ミズギワベンケイガニ (新称) P. liho Koller, Liu & Schubart, 2010, カクベンケイガニP. pictum (De Haan, 1835), ユビアカベンケイガニP. tripectinis (Shen, 1940)] について, 形態や色彩の特徴, 生息環境, 琉球列島における分布記録および分類学的な諸問題を記述した. これらの種のうち, ヨコスジベンケイガニ, ツメナガベンケイガニおよびミズギワベンケイガニは日本初記録となる. P. dumacenseの同定については, 原記載が雌1個体に基づいており, 雄の形質を重視する現在の同定方法には不充分な情報しか得られていない. また, P. dumacenseは形態的にP. kuekenthali (De Man, 1902) に類似することから, これらの種の分類学的位置を確定するためにはさらなる研究が必要である. さらに, P. lepidumとP. palauense (Takeda, 1972) は雄の可動指上面の瘤状顆粒数によって識別されるとされていたが (P. lepidum: 17–18 vs. P. palauense: 19), 本研究によりP. lepidumの瘤状顆粒数は16–20の間で変異することが確認されたため, P. palauenseの分類学的な位置付けについても再検討が必要である. 本報では, 文献情報に基づき, 琉球列島におけるクシテガニP. affine (De Haan, 1837) の分布記録についても言及した.



  • Fauna Ryukyuana

    Fauna Ryukyuana 23 1-41, 2015-08-25

    琉球大学資料館 (風樹館)


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