Observations on the Life History and Taxonomic Relationships of the Trematode Aspidogaster conchicola

Abstract

In 1827, von Baer described a trematode which he named Aspidogaster conchicola. The original material was from a fresh-water mussel of the genus Anodonta, from Prussia. This same species has long been known to occur in the pericardial and renal cavities of North American UNIONIDAE, but most of the studies carried on by American investigators have dealt chiefly with morphology and distribution of the species. Kelly (1899) carried on extensive studies of the host relationships of this species in the Illinois River and Stunkard (1917) made a study of the general morphology which confirms and adds somewhat to the earlier observations by Stafford (1896). There has been but fragmentary information concerning the development of this parasite of the UNIONIDAE. Stafford (1896), Faust and Tang (1936), and others have made the suggestion that the life cycle is fundamentally direct, i.e., that the young worm develops directly into an adult, either in the same host individual which shelters the mature worm, or in another individual of the same or of a different species. The systematic position of Aspidogaster has long been in doubt. Whether it belongs in MONOGENEA, DIGENEA, or an intermediate group has been a controversial question. It is the object of this paper to trace the life cycle of this worm and to review critically the evidence as to its systematic position. In the present study, the process of hatching of the eggs of Aspidogaster has been observed and, in natural infections, series of immature stages have been found representing fairly complete developmental stages all within the same host species. Aspidogaster conchicola therefore differs from the general pattern of host-parasite relationship among trematodes in that the entire life cycle occurs within an invertebrate host. UNIONIDAE from the Sangamon River near Mahomet, Illinois; from the Salt Fork, at Homer Park, Illinois; and from the Wabash River at West York, Illinois, are the hosts of the Aspidogaster used in this study. A detailed list of the host species will be presented in another paper dealing more directly with relationships to the host.