First report of Subulura sp. (Ascaridoidea, Subuluridae) parasitizing Cerdocyon thous (Carnivora, Canidae) in a fragment of Atlantic forest in the state of Rio de Janeiro, Brazil Luís Cláudio Muniz-Pereira1,3, Fabiano Matos Vieira1,3, Cecília Bueno1, and Paula Araujo Gonçalves1,2 1Laboratório de Helmintos Parasitos de Vertebrados (LHPV), Instituto Oswaldo Cruz (IOC), FIOCRUZ, Av. Brasil 4365, Rio de Janeiro, RJ, CEP 21040-900, Brazil. 2Laboratório de Ecologia, Universidade Veiga de Almeida, Rua Ibituruna, 108, Rio de Janeiro, RJ, CEP 20271-901, Brazil. 3Programa de Pós-graduação em Biodiversidade e Saúde (PPGBS), IOC, FIOCRUZ, Rio de Janeiro The genus Subulura Molin, 1860 (Ascaridida, Subuluridae) has approximately 23 nominal species in Brazil, of which two are parasites of mammals. However, the parasitism by species of this genus in wild carnivorous mammals can still be considered scarce in Brazil. The current study aims to report for the first time the parasitism by Subulura in a wild canid in Brazil. One specimen of Cerdocyon thous (Carnivora, Canidae) road killed in a stretch of BR-040 highway, near to municipality of Petrópolis (22º 30' 18" S, 43º 10' 43" W), in the state of Rio de Janeiro, Brazil, was analyzed for helminth. Nematodes were collected in small intestine, fixed in cold 4% formalin by 15 days and stored in 70°GL ethanol. For identification, the nematodes were cleared in Amann’s lactofenol and mounted in temporary slides, for microscopic identification. The specimens of nematodes analyzed in the current study were identified as Subulura because they had hexagonal buccal opening located dorsoventrally, with three lips; well developed sclerotized and thickly walled buccal capsule; anterior end of oesophagus prolonged into three sclerotized small teeth; oesophagus with posterior bulb; lateral alae present; and male with caudal sucker. In mammals from Brazil two species of Subulura were previously reported: Subulura interrogans Lent & Freitas, 1935 as a parasite of marsupials from the states of Pará and Rio de Janeiro, and Subulura amazonica Pereira & Machado Filho, 1968 parasitizing Caluromys philander (Linnaeus, 1758) (Didelphimorphia, Didelphidae) from the state of Amazonas. Both species of Subulura were also recorded in Ptenomura brasiliensis (Gmelin, 1788) (Carnivora, Mustelidae) in the state of Amazonas, and this is the only one report of Subulura spp in wild carnivore mammals from Brazil. The specimens of Subulura sp. of the current study not resemble these two species that occurs in Brazilian mammals, because it has a body alae, which is also occurs in S. interrogans, but was not described em S. amazonica. Subulura sp. differs of S. interrogans by having 11 pairs of caudal papillae (5 precloacal, 2 adcloacal, and 4 postcloacal), while S. interrogans has 12 pairs of caudal papillae (4 precloacal, 2 adcloacal and 6 postclocal). Therefore, this morphotype of Subulura analyzed in the current study has not yet been observed in Brazilian mammals. New morphometric, morphological and genetic studies with these specimens of Subulura need to be performed in order to verify a new occurrence in mammals or a possible new species. .