A new hypothesis of decapod phylogeny

A cladistic analysis based on external morphology was carried out on 60 taxa of decapod crustaceans. An analysis with unordered characters and one with ordered characters were both in agreement regarding the major relationships. The ordered analysis gave better resolution of more advanced clades, while the unordered analysis gave better resolution of more basal clades. None of the traditional groups Palinura, Anomura, and Macrura is monophyletic. A new classification of decapod crustaceans is proposed. Homarida and Astacida are closely related, as shown by the unique process on the ischium of their first pereiopods. Glypheoidea forms the sister group to Astacura, within an enlarged Astacidea. Achelata is the sister group to Meiura (Anomala + Brachyura) in a new clade, Eurysternalia, characterized by a unique antennular morphology and by the eponymous wide sternum of its members. Thalassinida emerge as the sister group to Eurysternalia, in a new clade, Sterropoda, characterized by fusion of the first segments of the thoracic limbs. The fractostern is interpreted to be a eureptant feature, and a possible burrowing habitus is posited for the ancestral Eureptantia.