First record of Pachysentis canicola (Acanthocephala:Oligacanthorhynchida) and the occurrence of Mesocestoides sp. tetrathyridia (Cestoidea:Cyclophyllidea) in the western diamondback rattlesnake, Crotalus atrox (Serpentes:Viperidae).

This paper represents the first documentation and description of Pachysentis canicola cystacanths and the first report of a Pachysentis sp. in a paratenic reptile from the Americas. The western diamondback rattlesnake (Crotalus atrox) is also listed as a new host for tetrathyridia of the cyclophyllidean cestode (Mesocestoides sp.) and for the cystacanths of the oligacanthoryhynchid acanthocephalan (P. canicola). Six rattlesnake specimens were examined from Nolan County (32.30 degrees N, 100.39 degrees W), Texas. Four snakes (67%) were found parasitized with between 3 and 16 (mean 7) encapsulated tetrathyridia and 1 host additionally was infected with 6 P. canicola cystacanths within its mesentery.