Another piece of the living fossil puzzle: A new species of Polymixia Lowe, 1836 (Polymixiiformes: Polymixiidae) from the western South Atlantic

The family Polymixiidae is an ancient group of acanthomorph fish, often regarded as living fossils. Currently, there are 11 valid species allocated in the genus Polymixia, and commonly known as beardfish. All species are benthopelagic and can be found at depths between 80 and 800 meters, in the Atlantic, Indian, and Pacific oceans. Traditionally, only two species had been assigned to the Atlantic Ocean, P. lowei, in the western Atlantic, and P. nobilis, in the North Atlantic, including northern South America and Saint Peter and Saint Paul Archipelago; however, recent studies revealed a cryptic species from the Bermudas, described as P. hollisterae, and a yet undescribed species from the Caribbean Sea. Herein, we describe a new species of Polymixia from the western South Atlantic, which was previously confused with P. lowei. The new species is supported by both morphological and molecular evidence and can be distinguished among its congeners by a combination of characters, including counts of gill rakers, pyloric caeca, and dorsal-fin rays, arrangement of scales spines, and the shape of preopercle. The new species is distributed on the upper continental slope in Brazil, from Bahia to Rio Grande do Sul, and Uruguay, between 160 and 600 meters deep.