The significance of female dimorphic characters of primary freshwater crabs for the systematics of Eubrachyura (Crustacea: Decapoda: Brachyura)

Abstract

Abstract Male pleopods, pleon, and gonopods 1 and 2 of primary brachyuran freshwater crabs have been used for well over 100 years as important taxonomic characters to distinguish between species, genera, and families. In contrast, while there have been a number of studies of female dimorphic brachyuran characters, including two families of primary freshwater crabs, their pleopods have been virtually ignored and presumed to be uninformative with respect to systematics. Consequently, we provide for the first-time descriptions and images of the female pleon, pleopods, egg attachment sites, and telson of representatives of five primary freshwater crab families: Potamidae, Potamonautidae, Gecarcinucidae, Pseudothelphusidae, and Trichodactylidae. For preliminary comparative purposes, similar details are also presented for species representing two Heterotremata families, e.g., Epialtidae and Portunidae, and four Thoracotremata families e.g., Gecarcinidae, Grapsidae, Sesarmidae, and Varunidae. This morphological comparative study of female characters provides a new dataset for family-level comparisons of freshwater crabs. As a result, two groups of primary freshwater crabs are recognized: a revised Potamoidea Ortmann, 1896 for Potamidae, Potamonautidae, Deckeniidae, Gecarcinucidae, Pseudothelphusidae, and Epiloboceridae, and Trichodactyloidea comprising Trichodactylidae. Although all of the non-trichodactylid freshwater crab families are morphological heterotremes with male coxal gonopores and female sternal gonopores, their current Heterotremata assignment is here being questioned. From new evidence presented here, this group of primary freshwater Brachyura may be more properly positioned outside of Heterotremata, as a sister group of Thoracotremata. This use of novel female diagnostic characters, however, supports the continued assignment of Trichodactylidae to Heterotremata.