The saber-toothed blenny genus Petroscirtes Rüppell, 1830, including 11 valid species from the Indo-West Pacific Ocean, is characterized by the following combination of features: no fleshy blade-like crest on head; lower margin of gill opening not reaching to upper margin of pectoral-fin base; canine teeth in lower jaw without deep groove along anterior surface; dorsal and anal fins attached by membrane to body at caudal-fin base; dorsal fin with 10–12 spines and 14–21 soft rays; dorsal fin without notches between portions of spines and soft rays; anal fin with 2 spines and 14–21 soft rays; caudal fin with 11 rays, pectoral fin with 13–16 (usually 13 or 14) rays, pelvic fin with 1 spine and 3 soft rays; all fin rays unbranched; and cirri present on head (absent only in P. marginatus SmithVaniz, 1976). Two specimens (34.1–37.8 mm standard length; SL) of saber-toothed blenny, collected from Aka-jima Island (Kerama Islands) and Yaku-shima Island (Osumi Islands), Japan in 2010 and 2022, respectively, were subsequently identified as Petroscirtes xestus Jordan and Seale, 1906, having the following characteristics: fringed flaps on each side of chin; first dorsal-fin spine moderately elongate (shorter than second and fourth spines); 5 supratemporal pores; body depth at anal-fin origin 19.3–20.5% of SL; a dark brown stripe from eye to caudal-fin base; a series of submarginal black spots on dorsal fin; a black spot between first two dorsal spines. An Indo-West Pacific species, P. xestus has previously been recorded from Mozambique to Micronesia, and in Japanese waters, only from Miyakojima Island (based on an underwater photograph). Therefore, the present specimens represent the first specimen-based records of P. xestus from Japan, that from Yaku-shima Island being the northernmost record for the species. The new standard Japanese name “Kazahana-nijigimpo” is herein proposed for the species.
