Structure of Leptorhynchoides thecatus and Pomphorhynchus bulbocolli (Acanthocephala) eggs in habitat partitioning and transmission.

The role of egg structure in transmission and habitat use of Leptorhynchoides thecatus and Pomphorhynchus bulbocolli (Acanthocephala) was investigated. During storage in tap water at 4 C, the outer membrane of L. thecatus eggs was lost, releasing ribbonlike filaments of the fibrillar coat. After similar storage, the outer membrane and fibrillar coat of P. bulbocolli eggs remained intact. Eggs of L. thecatus entangled in algae, whereas those of P. bulbocolli settled to the substratum. Leptorhynchoides thecatus infections in amphipod intermediate hosts were significantly more prevalent and dense when eggs were allowed to entangle than when they were not. Prevalence and relative density of P. bulbocolli infections in amphipods were not significantly different between trials in which entanglement was possible and those in which it was not. These results indicate that although the same species of amphipod, Hyalella azteca, is the intermediate host for both acanthocephalan species, mechanisms of transmission differ. Differences in fibrillar coats result in segregation of the environment in a manner that affects transmission and occurrence in intermediate hosts.