Sphenophrya-like Ciliates of Oysters


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Sphenophrya-like ciliates, sphenophyriid infection.

Scientific name or taxonomic affiliation

Sphenophrya-like ciliates.

Geographic distribution

On oysters from eastern and western U.S., Canada, Europe and Scandinavia. May be ubuquitous.

Host species

Crassostrea virginica, Crassostrea gigas, Ostrea edulis and other bivalves including mussels, clams and cockles. Different species may occur in different species of oysters.

Impact on the host

Effects not well-established. Large numbers can be observed with no obvious host-response. Small numbers (fewer than 1%) are intracellular and may cause massive hypertrophy of the host cell and its nucleus (xenoma). The only pathology described to date was this xenomic response reported for sphenophyrids from C. virginica from the eastern United States. No mortalities have been associated with sphenophryiid infections.

Diagnostic techniques

Histology: Examine transverse sections through the gill and palp area for pear-shaped ciliates with large, densely basophilic nuclei attached to the gill and palp surfaces. More rarely found within the gill epithelium with or without xenoma.

Methods of control

No known methods of prevention or control.


Fenchel, T. 1965. Ciliates from Scandinavian Molluscs. Ophelia 2(1): 71-174.

Otto, S. V., Harshbarger, J. C. and Chang, S. C. 1979. Status of selected unicellular eucaryote pathogens, and prevalence and histopathology of inclusions containing obligate prokaryote parasites in commercial bivalve mollusks from Maryland estuaries. Haliotis 8 (1977): 285-295.

Sprague, V. 1970. Some protozoan parasites and hyperparasites in marine bivalve molluscs. American Fisheries Society Special Publication 5: 511-526.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Sphenophrya-like Ciliates of Oysters.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: