Description of a new cryptic, shallow-water tonguefish (Pleuronectiformes: Cynoglossidae: Symphurus) from the western North Pacific Ocean.

Combined results based on morphological characters and analyses of partial sequences of the 16s rRNA and coI genes confirm the validity of a new, cryptic, symphurine tonguefish from the western North Pacific Ocean. Symphurus leucochilus n. sp., a diminutive species reaching sizes to c. 67 mm standard length, is described from nine specimens that were collected from fish-landing ports and from trawls made at c. 150 m off Taiwan and Japan. Symphurus leucochilus shares many similar features with those of Symphurus microrhynchus and that of several undescribed species that are morphologically similar to S. microrhynchus. Symphurus leucochilus has also been misidentified as Symphurus orientalis in fish collections because of shared similarities in some aspects of their morphology. The new species differs from all congeners by the following combination of meristic, morphological and pigmentation features: a predominant 1-2-2-2-2 pattern of interdigitation of proximal dorsal-fin pterygiophores and neural spines; 12 caudal-fin rays; 89-92 dorsal-fin rays; 76-80 anal-fin rays; 49-51 total vertebrae; four hypurals; 75-83 longitudinal scale rows; 32-35 transverse scales; 15-17 scale rows on the head posterior to the lower orbit; absence of a fleshy ridge on the ocular-side lower jaw and a membranous connection between the anterior nostril and lower part of the eye; a narrow interorbital space and dorsal-fin origin anterior to the vertical through the anterior margin of the upper eye; absence of both dermal spots at bases of anterior dorsal-fin rays and melanophores on the isthmus; uniformly yellow to light-brown ocular-side colouration without bands; dorsal and anal fins with alternating series of dark rectangular blotches and unpigmented areas; a uniform white blind side and a bluish-black peritoneum. Despite overall similarities in morphology between S. leucochilus and S. orientalis, as well as between two of the nominal species morphologically similar to S. microrhynchus, analyses of partial 16s rRNA and coI gene sequences show that S. leucochilus, S. orientalis and the two other nominal species represent three distinct lineages within the genus Symphurus.