Abstract
Five new species (Unionicola (Parasitatax) dimocki, arcuatoides, bishopi, cooki and tumidoides) are described for the first time. All species in Parasitatax are mussel parasites. The species of the subgenus are re-evaluated, and distribution and host records are reported for U. ypsilophora (Bonz), U. arcuata (Wolcott), U. tumida (Wolcott) and U. thienemanni Viets.