Abstract
A cauda-like structure was found, firstly in Cunaxidae, and with it the new taxa Cunaxicaudinae Chen & Jin subfam. nov., and its two new genera, Cunaxicaudus Chen & Jin gen. nov. (type genus) and Brevicaudus Chen & Jin gen. nov., were erected. Cunaxicaudinae Chen & Jin subfam. nov. differs from the known members of the family Cunaxidae by the unique conspicuous cauda derived from the posterior end of the hysterosoma. The generic features of Cunaxicaudus Chen & Jin gen. nov. are as follows: the posterior of the hysterosoma elongated as a much longer cauda; palp between genu and tibiotarsus without apophysis; e1 closer to d1 than f1; and e1 closer to mid-line than c1 and d1. The generic features of Brevicaudus Chen & Jin gen. nov. are as follows: the posterior of hysterosoma elongated as a short cauda; palp between genu and tibiotarsus with one apophysis; distance between setae e1 and d1 approximately equal to e1; and f1, e1 as close to mid-line as c1 and d1 to mid-line. It is proposed that the specialized cauda may be the result of the evolution of the sperm transfer mode.