A new sentinel crab of the genus Euplax H. Milne Edwards, 1852 (Crustacea: Decapoda: Brachyura: Macrophthalmidae) from Palau Islands and Ryukyu Islands, Japan

Abstract

Members of the Macrophthalmidae occur commonly in the Indo-West Pacific. Among the recent revisions of the Macrophthalminae, Mendoza & Ng (2007) revised the subgenus Euplax. And then, McLay et al. (2010) and Kishino et al. (2011) regarded Euplax H. Milne Edwards, 1852 as the valid genus. We collected an unusual macrophthalmid crab from shallow subtidal muddy bottoms in the Milky Way lagoon, Palau Islands and Kabira bay of the Ishigaki Island, Ryukyu Islands, Japan. The specimens appears similar to Euplax (H. Milne Edwards, 1852) species in having the following features: 1) the carapace is less than 1.26 times as wide as long 2) the front is slightly constricted at base of eyestalks 3) the external orbital angle is small and blunt, and the lower orbital border is with small granules 4) the central region of the epistome is concave, and its posterior margin is without no rim 5) the merus of the third maxilliped is distinctly shorter than the ischium 6) the dactylus of male cheliped arms with small differentiated tooth on the cutting margin. The genus Euplax has contained two species as Euplax dagohoyi (Mendoza & Ng, 2007) and E. leptophthalmus (H. Milne Edwards, 1852), but the present specimens can be distinguished from two congeners by combination of the characters of the eyes and chelipeds. The present poster is described on the species as new to science, herein.uplax H. Milne Edwards, 1852 as the valid genus. We collected an unusual macrophthalmid crab from shallow subtidal muddy bottoms in the Milky Way lagoon, Palau Islands and Kabira bay of the Ishigaki Island, Ryukyu Islands, Japan. The specimens appears similar to Euplax (H. Milne Edwards, 1852) species in having the following features: 1) the carapace is less than 1.26 times as wide as long 2) the front is slightly constricted at base of eyestalks 3) the external orbital angle is small and blunt, and the lower orbital border is with small granules 4) the central region of the epistome is concave, and its posterior margin is without no rim 5) the merus of the third maxilliped is distinctly shorter than the ischium 6) the dactylus of male cheliped arms with small differentiated tooth on the cutting margin. The genus Euplax has contained two species as Euplax dagohoyi (Mendoza & Ng, 2007) and E. leptophthalmus (H. Milne Edwards, 1852), but the present specimens can be distinguished from two congeners by combination of the characters of the eyes and chelipeds. The present poster is described on the species as new to science, herein.