Phymactis papillosa is a rocky shore sea anemone that is commonly found in the Pacific Ocean, from the Gulf of California to Tierra del Fuego, and in the Mar del Plata region, Argentina. The genus Phymactis is closely related to Bunodosoma and, due to character plasticity, a number of misidentifications have occurred. Therefore, the presence of P. papillosa in Argentina has been doubted but the matter had not been investigated in detail. Here we analyse P. papillosa specimens from Argentina and compare them, using molecular and morphological markers, to specimens from the species' type locality. In a phylogenetic analysis using 19 allozyme markers and ribosomal internal transcribed spacers sequences of different sea anemone genera, including all West Atlantic Bunodosoma species, we have found that the specimens from Argentina were genetically divergent from P. papillosa from Chile and closely related to West Atlantic Bunodosoma species. The genetic and morphological analyses indicate that those specimens belong to a new species of the genus Bunodosoma, described here as B. zamponii sp. nov.