Highly pathogenic scallop apicomplexan confirmed in gray meat (adductor muscle) Atlantic sea scallops Placopecten magellanicus. Identical apicomplexan found in populations of Iceland and Queen scallop species. Intermediate “brown” stage associated with progression of infection. Apicomplexan found in all gray and brown meat scallops, rarely in white meat scallops. Numerous developmental stages of the parasite present in various organs of the scallops. Severe myodegeneration observed in gray meat scallop tissues.