Abstract
A description is given for a new species of water mites belonging to the genus Unionicola. Adults and nymphs of the mite are residence the mantle cavity of the molluscan bivalve Anodonta rubens, while the other developmental stages are inhabiting the gills of the host. The descriptive characters of the present species are in accordance with those of superfamily, family and the genus. The present species has a specific characters compared with characters of other species of the same genus. The specific characters of the present species, the identity of the host and its distribution in the River Nile in Egypt and the description of mite for the first time suggested the present mite is a new species belonging to the genus Unionicola.