The Acanthocephalan Genus Corynosoma. I. The Species Found in Water Birds of North America

Abstract

Individuals of the acanthocephalan genus Corynosoma reach sexual maturity in the digestive tract of birds and mammals, especially those in aquatic habitats or those feeding on fish or aquatic invertebrates which serve Corynosoma as intermediate hosts. Although the same species has often been reported from both aquatic birds and mammals, Lundstr6m (1941) has recently reviewed the evidences which seem to discount the possibility that both of these groups serve as normal to the same species of Corynosoma. In observations on the two best known representatives of the genus in Europe, Corynosoma strumosum and C. sermerme, Lundstr6m's results support those earlier announced by Forssell (1904, 1905). Both of these species are normal parasites in the intestine of fish-eating mammals, especially seals. Although both species likewise occur often in the intestine of water birds they never attain full functional maturity in these hosts. Larvae of these two species, in the bodies of fish, may be introduced into the digestive tract of birds that prey upon fish but the worms fail to prosper there sufficiently to bring their eggs to full maturity. Evidence of this sort constitutes one of the most valid indictments of the meaningless expansions of host lists which received so much attention on the part of parasitologists, particularly a generation ago. An analysis has been made of numerous collections of Corynosoma from various parts of North America. On this continent there are some species which normally parasitize birds and other species which infect mammals. There are no clearly marked evidences of infections occurring in the alternative group such as have been found for the European species. In the present paper, only those species which infect water birds of North America will be considered. One of these is a well known species, Corynosoma constrictum Van Cleave, 1918; the other is a new species here described as Corynosoma anatarium n. sp. Other taxonomic and morphological studies on Corynosoma are in the course of preparation for publication. In 1918, the writer described and named Corynosoma constrictum, the first valid species of the genus to be recorded from North American water birds. The material upon which the description was based had been collected by Dr. Edwin Linton from the intestine of the American scoter (Oidemia americana Swainson) on Yellowstone Lake in Wyoming. Dr. Linton (1892) had mistakenly identified the worms as Echinorhynchus striatus Goeze a species described from European water birds. The specific identity and generic assignment of this European species were long under discussion (Liihe, 1911) although Meyer (1931, 1932-3) more recently ascribed it to the genus Polymorphus. As pointed out by the present writer in 1918, the males of Linton's original specimens had conspicuous cuticular spines on the fore body (Fig. 10) and around the posterior extremity in the region of the genital pore. This last statement alone is proof of the fact that the individuals are of the genus Corynosoma. The genital spines were shown clearly in Linton's