Description of a new cryptic species of tonguefish (Pleuronectiformes: Cynoglossidae: Symphurus) from shallow waters off Japan

Symphurus longirostris, a new, cryptic tonguefish, was discovered by combining evidence from both morphological characters and the genetic divergence data of partial sequences of the 16S rRNA and COI genes. This dwarf species, reaching sizes to 65.5 mm standard length (SL), is described from 37 specimens collected from shallow waters around southern and central Japan. Compared with congeners, S. longirostris shares many morphological similarities with those of S. microrhynchus, S. holothuriae, and several undescribed species that are morphologically similar to S. microrhynchus. Symphurus longirostris differs from all congeners by the following combination of characters: a predominant 1–2–2–2–2 ID pattern; 12 caudal-fin rays; 9 abdominal vertebrae; 45–48 total vertebrae; four hypurals; 81–88 dorsal-fin rays; 68–74 anal-fin rays; 56–66 longitudinal scale rows; 21–26 transverse scales; 11–14 scale rows on the head posterior to lower orbit; a well-developed fleshy ridge on the ocular-side lower jaw; a membrane covering both eyes that is continuous with the anterior nostril; distinct spots present in the dermis at the bases of the anterior dorsal- and anal-fin rays; the dorsalmost aspect of the peritoneum bluish black; the upper head lobe larger than lower head lobe; relatively short lengths of the head (HL 20.5–22.6 % of SL) and postorbital region (POL 13.0–14.9 % of SL); relatively long snout (SNL 18.7–24.4 % of HL); and relatively long predorsal length (PDL 23.8–32.7 % of HL) compared with corresponding features in S. microrhynchus and S. holothuriae. Analysis of morphological and molecular features in this description of S. longirostris will also help to clarify the status of the poorly known species, S. microrhynchus and S. holothuriae. This study is the beginning of a taxonomic revision of shallow-water species of Symphurus from the Indo-West Pacific.