Clarifying the Labrisomus Conundrum: Deep Divergence, Cryptic Lineages, and a Genetic Melting Pot in the Atlantic Ocean (Teleostei, Labrisomidae)

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ABSTRACT Aim We evaluate the phylogenetic relationships and taxonomic validity of Atlantic species of Labrisomus , identifying the lineages currently assigned to L. nuchipinnis , and assessing the role of biogeographic barriers in shaping the evolutionary history and geographic distribution of the genus. Location Atlantic Ocean. Taxon Labrisomus . Methods We assembled an extensive mitochondrial and nuclear DNA dataset of Atlantic species of Labrisomus to perform multi‐locus phylogenetic divergence‐time and historical biogeographic analyses, reconstruct haplotype networks, estimate genetic distances, implement lineage delimitation tests and estimate migration rates. Results Labrisomus nuchipinnis is a species complex comprising three deeply divergent lineages: one broadly distributed in the western Atlantic, another restricted to Florida (USA), and a third mostly distributed in the eastern Atlantic. A new usage of L. nuchipinnis is proposed, with the species restricted to the western Atlantic, and with the revalidation of Clinus canariensis (as L. canariensis ) for the mostly eastern Atlantic lineage. Despite their anatomical similarity, L. nuchipinnis and its Atlantic congeners diverge significantly genetically. Unusual genetic connectivity between samples of L. canariensis from the eastern Atlantic and southern Brazil suggests a potential trans‐Atlantic genetic pathway. Main Conclusion The deep genetic divergence among lineages previously included in the L. nuchipinnis complex contrasts with their anatomical similarity, making Labrisomus one of the most challenging cases of cryptic diversification among reef fishes. The evolutionary history of the genus likely involved spatial segregation driven by ecological niche overlap. Ecological factors may influence distribution patterns among species of the genus more strongly than geographic distance. The apparently isolated population of L. canariensis off southern Brazil provides a well‐documented case of disjunct distribution of a reef fish species between the eastern Atlantic and south Brazil, highlighting the potential of this region as a melting‐pot of biodiversity.

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