Abstract
The Hymenosomatidae is unique among the Brachyura on the basis of spermatozoal ultrastructure and morphological characters of the adults and larvae. The location of the hymenosomatid male gonopore, always a controversial question, is here shown to besternal, not coxo-sternal. This disposition, analogous to the arrangement of Thoracotremata, contradicts all morphological characters that indicate a heterotreme affiliation, close to the Majoidea and Dorippoidea. Molecular data also support such an assignment. The multiple hymenosomatid plesiomorphies are reviewed. The exceptional male reproductive system, a new scheme for the Eubrachyura, is assumed, at least in part, to be the result of a strong car-cinisation in an ancient, deeply rooted group, at present the most ecologically diverse in Brachyura. The presence of the Hymenosomatidae on the former Gondwanan landmasses and its worldwide pattern of distribution are consistent with the hypothesis of a Gondwanan origin of the family.
NSTL