Abstract
The present investigation was designed to assess the extent of sexual variations in some taxonomical paramerters in the populations of water mites Unionicola anodontae, U. niloticus and U. palpatus, collected from the freshwater mussel Anodonta rubens living in River Nile. The primary sexual differences are the presence of genital flaps in females and genital skeleton in males. The secondary sexual characters include dimensions and general shapes of body and its different parts, in addition to the meristic characters. X2 values of 28 meristic characters for females and males of the three species, are significant , at P levels from 0.01-0.001