Nematode parasitism in amphibians and reptiles

Nematodes of amphibians and reptiles comprise five main groups: Enoplida, Oxyurida, Strongylida, Ascaridida, and Spirurida. Systematics, geographical distribution, and host range point to parasitic relationships that extend well back into tetrapod history. Some parasite groups such as the Enoplida were acquired from other vertebrate groups by host transfer, a common theme in the evolution of new nematode taxa. Most nematodes of amphibians and reptiles, however, evolved primarily in these hosts. Oxyurida in reptiles and amphibians are more primitive than forms they gave rise to in mammals. They closely resemble the Oxyurida of invertebrates. Strongylida possibly evolved in Mesozoic archosaurian reptiles such as dinosaurs and early birds. They are now mainly parasitic in mammals, although distinct groups of strongyloids, trichostrongyloids, and diaphanocephaloids evolved in amphibians and reptiles, probably in the early Cenozoic. Ascaridida evolved in mid-Mesozoic or earlier amphibians and reptiles, and the most primitive representatives (Cosmocercoidea) are common today in anurans, saurians, and chelonians. From these the other superfamilies evolved. Survivors of the early radiations include primitive Heterakoidea in anurans and saurians, primitive Ascaridoidea in crocodiles, and Seuratoidea in a wide variety of all vertebrate subclasses. Most superfamilies of Spirurida evolved in mammals, birds or extinct groups. Forms in amphibians and reptiles, however, are at least Mesozoic in age.