Abstract
During the spring of 1984, the ciliateBalantidium prionuriumn. sp. was collected from the intestinal lumen of the herbivorous surgeonfish,Prionurus punctatus, from the Gulf of California. The symbionts were found in five fish from two well separated collection sites. Morphostatic specimens average 51 μm x 42 μm, and thus fall within the size range of several other fish balantidia. But the presence ofBalantidiumin a saltwater fish has not been reported, and such a host difference alone supports at least provisional recognition of this organism as a new species.