Comparative Morphology of Six Species of Strongyloides (Nematoda) and Redefinition of the Genus

To establish criteria for specific identification of Strongyloides, detailed descriptions were made of the parasitic and free-living stages of S. stercoralis, S. fiilleborni, S. cebus, S. myopotami, S. venezuelensis, S. ratti, and seven new species (to be reported later). Certain features were found to be constant and these formed a basis for a detailed definition of the genus. The number and arrange- ment of genital papillae in the free-living male and the cephalic papillae of the adult stages of both sexes, although previously reported to vary from species to species, were found to be constant within the genus. The excretory system of the parasitic female and the intestinal cell patterns in the larval and adult stages are newly described. The character of the ovaries and the stoma of the parasitic female, and the stages passed in the feces, were found to be useful in the identification of species, as were also, in some cases, certain features of the free-living adults and filariform larvae. The shape of the stoma, viewed from the en face position, proved to be the most useful single diagnostic feature. The diagnosis of the superfamily Rhabdiasoidea is emended. Concurrent infections of S. venezuelensis and S. ratti were found in wild rats for the first time. The importance of species identification of strains of Strongyloides isolated for experimental studies from rats and other animals was noted. A single-larva infection of S. venezuelensis was successfully established in the laboratory rat.