Two new species of Crustacea Copepoda parasitic on other Crustacea are described, both belonging to the family Nicothoidae. Homoeoscelis elongata n. sp., a parasite of a cumacean, is mainly characterized by the ventral situation of the cephalic region. Hadrothoe crenulata n. sp. resembles H. crosnieri, but differs from it by the structure and setation of the swimming legs. A key to the 20 genera of the Nicothoidae is provided as well as a checklist of the species of Nicothoidae, parasitic on cumaceans and decapods, with their locality.