Studies on the Coccidian Parasites (Apicomplexa: Eimeriidae and Pfeifferinellidae) of Pulmonate Gastropods1

Pulmonate and prosobranch gastropods collected in Minnesota and Washington were examined for the presence of coccidian parasites. Typical coccidian oocysts were recovered from the feces of 89 of 543 (16%) pulmonate snails representing the families Lymnaeidae, Physidae, Planorbidae, and Succineidae. No coccidial infections were apparent in 104 specimens representing the prosobranch families Viviparidae and Pleuroceridae. Oocysts identified as Pfeifferinella ellipsoides were recovered from 21 of 101 (21%) Stagnicola elodes, 2 of 94 (2%) Physa gyrina, and 4 of 67 (6%) Aplexa hypnorum although incidence of infection differed greatly (2–40%) dependent upon the locality sample. This coccidian has not been described previously from North America and is reported here from members of the families Lymnaeidae and Physidae for the first time. Twenty percent of Oxyloma retusa from one habitat were shedding oocysts slightly smaller than, but otherwise identical with, those of Alveocystis gugleri. A third as yet unidentified oocyst was recovered from up to 54% of Helisoma trivolvis. As a group, the coccidia of pulmonate molluscs have been poorly studied. The findings of this survey, however, suggest that these parasites may be more common and widely distributed in both the Basommatophora and Stylommatophora than previously believed.