Cosmocerca parva Travassos 1925 (Asca-ridida, Cosmocercoidea, Cosmocercidae) was originally described from Helosia nasus (Leptodactylidae) of Angra dos Reis, State of Rio de Janeiro, Brazil. It has also been reported in Leptodactylus chaquensis, L. elenae, Hyla fuscovaria and Bufo paracnemis from Paraguay (MR Baker & C Vaucher 1984 Rev Suisse Zool 91: 299-307). This note enlarges the known morphological variability of C. parva in a new host and makes amend for previous descriptions with the aid of scanning electron microscope (SEM) at the same time that presents the first record of Cosmocerca species in Argentina.Facultad de Ciencias Naturales y Museo