八重山諸島与那国島から得られたシシダマオオクチアマダイ（新称）Opistognathus variabilis（アゴアマダイ科）

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The cosmopolitan genus Opistognathus Cuvier, 1816, characterized by unforked dorsal-fin spines, currently comprises 64 valid species, including Opistognathus variabilis Smith-Vaniz, 2009, described on the basis of 71 specimens and widely known from the Maldives, Andaman Sea, Indonesia, Philippines, Palau, Taiwan, Ryukyu Islands and Vanuatu. However, the Japanese record was based solely on an underwater photograph taken off Iriomote Island, Ryukyu Islands. A single example of the species, collected from Yonaguni Island, Yaeyama Islands, represents the first record of the species from Japan supported by a voucher specimen. Opistognathus variabilis closely resembles Opistognathus albicaudatus Smith-Vaniz, 2011 and Opistognathus castelnaui Bleeker, 1860 in having an elongate upper jaw, numerous longitudinal scales and similar body coloration, including 7–10 dark blotches along the dorsal-fin base. However, the former can be distinguished from O. albicaudatus by the poreless Y-shaped area dorsally on the head (vs. absent) and 9–11 procurrent caudal-fin rays (vs. 6–7), and from O. castelnaui by having 68–92 longitudinal scale rows (vs. 90–110), the dorsal fin deeper posteriorly (vs. similar depth along entire length), a single stripe on the upper jaw inner surface (vs. two), and seven or eight mid-lateral blotches along the body (vs. three or four irregular dark horizontal lines and/or dark reticulations laterally on body). The new Japanese standard name “Shishidama-ohkuchi-amadai” is proposed for O. variabilis.