Fourteen species have either been described in, or referred to, the genus Euniphysa. Seven of these are here re-described based on type material and two new species, E. quadridentata and E. filibranchia, are described. Euniphysa oculata is found to be a subjective synonym of E. spinea, and E. unicusa is a subjective synonym of E. aculeata. Euniphysa taiwanensis and E. megalodus are correctly assigned to the genus, but cannot be described due to lack of material. Euniphysa misakiensis, E. tubicola and E. tubifex are transferred to Eunice. A key is given to the nine identifiable species retained in Euniphysa. Coding strategies for polymorphic and inapplicable characters, as well as problems associated with shared absences, are discussed. A phylogenetic analysis of Euniphysa based on 24 morphological characters yielded two most parsimonious trees (CI = 0.902, RI = 0.905). The tree topology separates Euniphysa into two distinct groups. Group I includes E. filibranchia n. sp., E. italica, E. jeffreysii, E. quadridentata n. sp. and E. spinea, it is supported by five equivocal similarities. Group II is supported by five unequivocal synapomorphies and two equivocal similarities, it includes E. aculeata, E. auriculata, E. falciseta and E. tridontesa. Based on the phylogenetic topology, Paraeuniphysa and Heterophysa are considered as junior synonyms of Euniphysa. The recognition of a separate family for Euniphysa is not warranted. All species of Euniphysa are fragile, shallow, warm water species. They have been collected mainly from sandy sediments of the Northern Hemisphere. The greatest diversity is from the South China Sea area; other species are found throughout the Indian Ocean, the Mediterranean Sea and the East Atlantic Ocean coasts suggesting the genus may have originated in the Tethys Sea. A few species have also been found in the Gulf of Mexico and the West Atlantic Ocean coast again suggesting a Tethyan origin associated with the westward drift of the North American continent.