Systematic relationships of the Atractidae and Cosmocercidae (Nematoda: Cosmocercoidea): two new atractids parasitic in amphibians and fish

Abstract

Raillietnema spectans Gomes, 1964 (Cosmocercinae) from Bufo paracnemis of Brazil is redescribed. The cephalic, oesophageal, and male caudal structures of this species are strikingly similar to Schrankiana freitasi n. sp. (Atractidae) from Leptodactylus pentadactylus of Brazil and Labeonema bainae n. sp. (Atractidae) from the fish Eutropius liberiensis of Gabon. Comparison of the cephalic, oesophageal, and female reproductive structures of the 21 genera of Atractidae reveals two primitive groups with characters suggesting an ancestral relationship with the didelphic Cosmocercinae: Schrankiana, Ibrahimia, Schrankianella, Labeonema with Cosmocercinae-like cephalic and oesophageal morphology, but monodelphic; and Probstmayria and Fitzsimmonsnema with a Cosmocercinae-like oesophagus and didelphic reproductive system, but with a modified cephalic end. A possible polyphyletic origin for the Atractidae cannot be excluded, although for the present the group remains classified as a single family distinguishable by its biology (viviparous) from the Cosmocercidae (oviparous).