ABSTRACT
The male reproductive system in the water mite Unionicola tetrafurcatus consists of a single accessory gland, 2 testes, each leads to a vas deferens, the latter leads to an ejaculatory duct and copulatory organ. The system is supported with a genital skeleton consisting of cella and brachia. Each testis is composed of a glandular and germinal parts. In the testis, the spermatogonia. spermatocytes, spermatids and sperms are distributed in a sequence from the dorsal to the ventral region. The acrosomal complex and the nuclear envelope of the sperms are absent. The testicular lumen is filled with secretion that contributes to sperm cell aggregation.