Polybius vernalis, the grey swimming crab, is a small, shallow-water crab in the family Portunidae. P. vernalis was believed to be a strictly Mediterranean speciesGarcía-Raso, E.; d'Udekem d'Acoz, C.; Moukrim, A.; Schubart, C.D.; Cuesta, J.A. (2024). A new cryptic species of Polybiidae (Crustacea: Decapoda: Portunoidea) from the East Atlantic, with considerations on the genus Polybius. European Journal of Taxonomy. 930: 277-313., available online at https://doi.org/10.5852/ejt.2024.930.2501, but newer evidence implies its presence in the North Sea is not that recent.
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