A new five-gilled species of <i>Myxine</i> (Myxinidae) from the western South Atlantic sheds light on the phylogenetic relationships and biogeography of the genus

Abstract Hagfishes (Myxinidae) are jawless, cartilaginous, eel-like craniates, known from 91 valid species distributed across all oceans from the surface to 2743 m depth. Traditionally, the family is divided into three subfamilies, with the genus Myxine comprising 26 valid species so far. Here, we describe a new species of Myxine from off southern Brazil and assess its phylogenetic position among other myxinids. Molecular data were generated from mitochondrial genes (16S and COI), and phylogenetic analyses were conducted using maximum likelihood and Bayesian methods. The new species differs from congeners in several morphological traits, including the total number of teeth cusps, number of anterior and posterior unicusps, number of caudal pores, and colour pattern. Phylogenetic analyses recovered the Myxininae and Eptatretinae as monophyletic sister groups, with the Rubicundinae as sister to that assemblage. In the Myxininae, the new species represents an early branch within Myxine, reinforcing the relevance of the South Atlantic in the early diversification of the genus.