Ancistrocoma pelseneeri and A. myae Ciliates of Clams


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Gill ciliates.

Scientific name or taxonomic affiliation

Ancistrocoma pelseneeri, Ancistrocoma myae and Ancistrocoma spp.

Geographic distribution


Host species

Mya arenaria, Mya irus, Mya inconspicua, Mya nasuta, Mya secta, Cryptomya californica, and probably other species of clams as well as oysters.

Impact on the host

The effect on clams not well-established. Large numbers can occur adjacent to the gills with no obvious host-response. However, Pauley et al. (1967) have described a host-defense response and suggest these ciliates may have an effect under adverse growing conditions.

Diagnostic techniques

Histology: Banana shaped ciliates with large granular and polymorphic nuclei on or adjacent to the gills.

Methods of control

These ciliates appear to be ubiquitous in distribution, although different species may occur in different clam species. All pathology described to date appears correlated to secondary factors.


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

Pauley, G.B., Chew, K.K. and Sparks, A.K. 1967. Experimental infection of oysters (Crassostrea gigas) with thigmotrichid ciliates. Journal of Invertebrate Pathology 9: 230-234.

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

van Banning, P. 1979. Protistan parasites observed in the European flat oyster (Ostrea edulis) and the cockle (Cerastoderma edule) from some coastal areas of the Netherlands. Haliotis 8 (1977): 33-37.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Ancistrocoma pelseneeri and A. myae Ciliates of Clams.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: