Leptocephalus larvae of two moray eels (Anguilliformes; Muraenidae), Gymnothorax sagmacephalus and Gymnothorax albimarginatus, identified from morphometric and genetic evidence

Two forms of muraenid leptocephali, collected from the western Pacific Ocean, were identified as Gymnothorax sagmacephalus Bohlke 1997 and Gymnothorax albimarginatus (Temminck and Schlegel 1846) on the basis of morphometric and genetic analyses. The leptocephali of each species were characterized, respectively, by counts of 172–175 and 186–191 myomeres, 43–44 and 47 predorsal myomeres, 109–113 and 127–134 preanal myomeres, and 100–104 and 118–119 last vertical blood vessel myomeres. Gymnothorax sagmacephalus leptocephali had minute melanophores over much of the head and body, closely resembling the condition in Gymnothorax minor (Temminck and Schlegel 1846), whereas those of G. albimarginatus not only had minute melanophores over much of the head and body, but also a pair of melanophore groups on the posteroventral and posterodorsal aspects of the head. Such groups are here considered to represent highly specific characters. Although a previous opinion postulated that G. sagmacephalus is a juvenile of G. albimarginatus, and the adult morphologies of the two species have a lot in common, they clearly differ in both leptocephalus morphology and genetic sequence. Therefore, G. sagmacephalus was concluded as being a valid species.