Data from: 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 characters, which are likely coupled functionally and interlinked evolutionarily: (1) the external part of the petasma and the posterior part of the thelycum and (2) the internal part of the petasma and anterior part of the thelycum. We reconstruct possible mating position during copulation for each of the new species groups presented here. We also present an updated key to species of Gennadas.

Gennadas属内的物种彼此间的差异主要仅存在于雄性交接器（petasma）与雌性交接器（thelycum）的交配特征上，本研究借助扫描电子显微镜（scanning electron microscopy）对这些特征进行了重新检视，并将其作为系统发育分析的核心依据。
本次研究共鉴定出26项雄性交接器特征与49项雌性交接器特征。所有已被正式确认的16种Gennadas属物种，以及外类群Aristaeomorpha foliacea均被纳入作为终端分类单元。分析结果得到4个稳健的单系群（monophyletic clades），并将其描述、界定为全新的物种类群。
相较于雄性交接器特征，雌性交接器特征对系统发育树形的拓扑结构影响更大，且对更深层级的演化节点具有更强的支持力度。据此我们提出假说：雌性交接器的相关特征先于雄性交接器特征发生演化。
相对更为保守的特征包括雌性交接器与雄性交接器的前侧腹甲部分，而雌性交接器上的盾片与突起，以及雄性交接器叶的形态与细分结构则呈现出演化可塑性。
我们鉴定出两类功能上偶联、演化上相互关联的交配特征：（1）雄性交接器的外部结构与雌性交接器的后部区域；（2）雄性交接器的内部结构与雌性交接器的前部区域。
我们为本文提出的每个新物种类群重建了交配过程中可能采用的体位。此外，本研究还更新了Gennadas属物种的分类检索表。