Gerris sp. is distinguished by several characteristics: the first antennal segment being shorter than 1.3 times the length of the head, the absence of sclerotization in the accessory gland, connexival corners being triangular and pointed (especially in males), a predominantly membranous dorsal part of the phallotheca, the basal plate of the vesica being fused with the dorsal plate or being absent, the lack of apical sclerites but the presence of rod-shaped ventral sclerites in the vesica, and the origin of the vermiform appendix in the female gynatrial complex from the top of the gynatrial sac. Gerri-selloides, on the other hand, is characterized by having a long median longitudinal groove on the meso- and metasternum, as well as other more general features such as the length ratio of the first segment of the middle tarsus being at most 2.5 times that of the second segment, and modifications to the first gonocoxa including being transversely impressed or flattened.