The congrid eel genus Gnathophis in Taiwan (Anguilliformes, Congridae), with descriptions of three new species

The genus Gnathophis differs from other genera of Congridae in having a moderately blunt and rounded tail tip and a slightly hardened tail extremity. The fleshy tip of the snout extends distinctly forwards beyond the intermaxillary teeth. A longitudinal fleshy keel is present on the ventral surface of the snout tip. Currently, two species of Gnathophis have been recorded from Taiwan, G. heterognathos and G. asanoi , whereas G. xenica has subsequently been determined to be a misidentification. In this study, three new species of the congrid eel genus Gnathophis Kaup are described from deep-sea waters off northeastern and southwestern Taiwan, based on 130 specimens. Gnathophis kbalanensis sp. nov . is diagnosed by the combination of blackish dorsal, caudal, and anal fins; 34–36 preanal vertebrae, 42–43 precaudal vertebrae, and 134–137 total vertebrae; 32–35 preanal lateral line pores; and elevated lateral line pores above the pectoral fin. Gnathophis melanurum sp. nov . is distinguished from its congeners by having whitish dorsal and anal fins and a blackish caudal fin; 28–32 preanal vertebrae, 37–41 precaudal vertebrae, and 98+–125 total vertebrae; 29–32 preanal lateral line pores; and elevated lateral line pores above the pectoral fin. Gnathophis nanhaiensis sp. nov . is separable from other species of Gnathophis in possessing whitish dorsal, caudal, and anal fins; 40–42 preanal vertebrae, 47–48 precaudal vertebrae, and 139–143 total vertebrae; 37–41 preanal lateral line pores; and lateral line pores above the pectoral fin that are not elevated. The validities of G. kbalanensis sp. nov . and G. melanurum sp. nov . are further supported by DNA barcoding analysis of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Molecular comparisons additionally indicate that specimens of G. heterognathos (Bleeker) from waters off Taiwan exhibit a maximum intraspecific COI sequence divergence of 1.4%.