An assessment of lesions in bay scallops Argopecten irradians attributed to Perkinsus karlssoni (Protozoa, Apicomplexa)

Lesions found in bay scallops Argopecten irradians imported into Atlantic Canada for culture were attributed to a parasite Perkinsus karlssoni. It appears, however, that stages from several organisms were combined to create the life cycle of P. karlssoni. The ultrastructure of the agent in lesions of bay scallops is not documented adequately to diagnose affinities to the genus Perkinsus. Furthermore, there was discrepancy as to whether P. karlssoni enlarged in fluid thioglycollate medium, and the shape and structure of the prezoosporangia as well as the movement and life span of the zoospores were not consistent with the genus Perkinsus. P. karlssoni cannot be considered as a species of Perkinsus.