Redescription of the bigeye chimaera, Hydrolagus macrophthalmus de Buen, 1959 (Chondrichthyes: Chimaeriformes), with a genetic characterization of the species

Abstract

Hydrolagus macrophthalmus de Buen, 1959 is a little known chimaerid species from the southeastern Pacific Ocean. At the time of its description, it was the only chimaeroid species known from the region; however, there now are four other Hydrolagus species known from the area. Hydrolagus macrophthalmus is distinct from other species in the area based on the following characters: an undulated second dorsal fin with peaks on the anterior and posterior regions, a long curved first dorsal fin spine that extends past the origin of the second dorsal fin when laid flat, and uniform dark brown color with a light spot on middle of the second dorsal fin that extends onto the body below it. Genetic sequencing of the NADH2 gene was used to distinguish H. macrophthalmus from other known species in the region. This species is herein re-described and compared to four sympatric species: H. alphus, H. melanophasma, H. mccoskeri, and H. trolli. The redescription of this species will improve identification and aid in the taxonomic resolution of Southeastern Pacific Ocean chimaeras. A key to species of Hydrolagus in the Southeastern Pacific Ocean is provided.