(NEMATODA: TRICHOSTRONGYLIDAE) FROM OSTRICHES IN NORTH AMERICA, WITH COMMENTS ON THE GENERA LIBYOSTRONGYLUS AND PARALIBYOSTRONGYLUS

Libyostrongylus dentatus sp. n. is described from ostriches on farms from North Carolina and Texas. Nematodes were recovered from the posterior proventriculus and under the koilon lining of the gizzard; the parasites occurred in mixed infections with Libyostrongylus douglassii. The species is distinguished from congeners by the presence of a prominent, dorsal, esophageal tooth; in males by the structure of the dorsal ray and spicules; and in females by small eggs (52-62 gm in length), a sublateral vulva situated at 93% of the body length from the anterior, and a strongly curled, digitate, tail with cuticular inflations at the anus. Conflicts in the generic diagnoses of Libyostrongylus and Paralibyostrongylus were apparent, based on the structure of the dorsal ray or position of rays 3-5 of the copulatory bursa. These can only be resolved based on phylogenetic analyses of the 11 nominal species referred to these genera. Although historically represented only in North American zoos, various species of ratites (emus Dromaius novaehollandiae (Latham), rheas Rhea americana Linnaeus, and ostriches Stru- thio camelus Linnaeus) have been gaining economic importance in the United States and southern Canada. Semiconfined to near free-ranging flocks are now widely distributed on ranches across temperate North America. Concurrent with more intensive hus- bandry of these avian species has been the renewed recognition of parasitism by helminths as an influence on production, mor- bidity, and mortality, e.g., Thieler and Robertson (1915), Barton and Seward (1993), and Button et al. (1993). Also it has become apparent that a substantial component of the typical parasite faunas (principally strongylate nematodes) associated with these hosts has been introduced from sub-Saharan Africa and South America and some pathogenic species now may be widely es- tablished in North America (Table I). Although the parasite faunas of ratites appear to be host specific and historically de- fined by biogeographic and host associations (Clay, 1957), the potential for cross-transmission to domesticated birds or avian taxa endemic to North America has yet to be established (nor has the reciprocal been considered in detail). The greatest po- tential for transmission resides with strongylate nematodes with direct life cycles. This burgeoning interest in ratites and their parasites has resulted in numerous submissions to the U.S. National Parasite Collection for confirmation or identification. Recently, material was submitted from isolated flocks of ostriches in North Car- olina and Texas, with a provisional identification of Amidos- tomum sp. based on the presence of a prominent esophageal tooth extending into the buccal cavity. It was later determined that these specimens represented a previously unrecognized spe- cies of Libyostrongylus Lane, 1923 (Trichostrongylidae: Li- byostrongylinae), which is described herein. Additionally, we provide the basis for readily distinguishing all species of Li- byostrongylus from ostriches, enabling rapid diagnosis, and comment on diagnostic characters for the genera Libyostron- gylus and Paralibyostrongylus Ortlepp, 1939.