Contribution to the phylogeny of Isopoda (Crustacia)

A cladistic analysis of the main isopod lineages (sub-orders) based on 75 a nd/or 76 morphological traits is presented with the aim of reconstructing t he phylogenetical relationships within the Isopoda and between this latter group and other malacostracan orders. Some of the morphological traits are used for the first time, others receive new interpretations. From this anal ysis, using the Amphipoda and Tanaidacea orders as outgroups, we infer the monophyletic origin of the Isopoda. Tanaidacea is the sister group of Isopo da. Phreatoicidea represents the most primitive isopod group. The microcerb erids, considering their peculiar male copulatory organ and many autapomorp hic traits, are considered, not a family of the Aselloidea, but a sub-order , the Microcerberoidea, the sister group of Asellota. The enigmatic group C alabozoidea appears related to the Oniscidea, as sister group.