The genus Gennadas (Benthesicymidae: Decapoda): morphology of copulatory characters, phylogeny and coevolution of genital structures

Species within Gennadas differ from each other largely only in male (petasma) and female (thelycum) copulatory characters, which were restudied in scanning electron microscopy and used as a basis for phylogenetic analyses. Twenty-six petasma characters and 49 thelycum characters were identified. All sixteen recognized species of Gennadas and Aristaeomorpha foliacea (outgroup) were included as terminals. Four robust monophyletic clades were retrieved, described and diagnosed as new species groups. The thelycum characters had greater impact on tree topology and supported deeper nodes than did the petasma characters. We hypothesize that aspects of the thelycum evolved first followed by aspects of the petasma. Relatively more conservative characters include parts of the anterior sternites of the thelycum and of the petasma, while the scuti and protuberances on the thelycum and the shape and subdivisions of the petasma lobes are evolutionary plastic. We identified two groups of copulatory ch...