Independent radiation of snailfishes into the hadal zone confirmed by Paraliparis selti sp. nov. (Perciformes: Liparidae) from the Atacama Trench, SE Pacific

Snailfishes are among the most rapidly radiating families of marine fishes, resulting in a global distribution from the coastal intertidal to deep subduction trenches. The true diversity and distribution of deep-water snailfishes, particularly at hadal depths (>6000 m) and in the Southern Hemisphere, remain uncertain due to the rarity of samples. Here, we present the snailfish diversity at near-hadal and hadal depths in the Atacama Trench, which runs along the southwest coast of South America. Using free-fall baited cameras and traps, we documented at least three species of hadal snailfishes between 5920 and 7608 m based on distinct morphologies. One snailfish specimen was recovered from 6714 m, which we describe herein as Paraliparis selti sp. nov., based on a combined morphological and molecular taxonomic approach (16S, COI, and Cyt-b). Paraliparis selti sp. nov. is morphologically distinct from described snailfishes due to a combination of high number of; vertebrae (65) particularly the abdominal vertebrae (12), dorsal fin rays (60), anal fin rays (52), and caudal fin rays (8); comparatively low number of pectoral fin rays (18) which forms a deep notch with two widely spaced non-rudimentary rays. Micro-CT was used to minimise dissection of the specimen and to provide a digital holotype. Paraliparis selti sp. nov. highlights the importance of the Liparidae at hadal depths and provides evidence for at least two independent radiations of snailfishes into the hadal zone.