Taxonomy and morphology of European pea crabs (Crustacea: Brachyura: Pinnotheridae)

Pea crabs distributed around the coasts of Europe live commensally inside bivalves and sea squirts. Even though just five species are described, their taxonomy is still under development. In order to produce standardized comparative descriptions, pea crabs were collected and studied from different hosts and localities in the Northeast Atlantic and the Mediterranean Sea. Because of the pinnotherids' sexual dimorphism, the male and female are described separately for every species. The common and widely distributed species Nepinnotheres pinnotheres (Linnaeus, 1758) and Pinnotheres pisum (Linnaeus, 1767) are redescribed, while the status of the questionable species Pinnotheres ascidicola Hesse, 1872 and Pinnotheres marioni Gourret, 1888 from sea squirts and Pinnotheres pectunculi Hesse, 1872 from the dog cockle, Glycymeris glycymeris, was finally clarified. According to the morphological analysis, Pinnotheres ascidicola and Pinnotheres marioni are junior synonyms of Nepinnotheres pinnotheres, whereas the status of Pinnotheres pectunculi as a valid species has been demonstrated.