Siphon Snails of Clams and Cockles


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Clam siphon snails.

Scientific name or taxonomic affiliation

Boonea spp., Odostomia spp. and Evalea tenuisculpta of the gastropod family Pyramidellidae.

Geographic distribution

Ubiquitous but most ectoparasitic species have been reported from the North Atlantic Ocean. On the Pacific Ocean coast of North America, Odostomia spp. were reported from British Columbia, Canada (Vancouver Harbour, the west coast of Vancouver Island (Clayoquot Sound), and at the north east end of Vancouver Island) and on the coast of Alaska (Harbo et al. 2012). Evalea tenuisculpta was reported from British Columbia, Canada (Vancouver Harbour in Indian and Port Moody Arms) and in Washington State, U.S.A. (Harbo et al. 2012).

Host species

In the North Atlantic Ocean, ectoparasitic snails were reported from Mya arenaria, Cerastoderma (=Cardium) edule, Cardium lamarcki, Saxicava rugosa and Tellina spp. as well as many species of oyster, mussel and scallop. On the Pacific Ocean coast of North America, they were reported from Tresus capax, Hiatella arctica and Entodesma navicula as well as rock scallops (Crassadoma gigantea), mussels (Mytilus sp.) and chitons (Mopalia sp.) (Harbo et al. 2012).

Impact on the host

Pyramidellids normally occur close to the mantle edge on the shell of the host. However, on clams they attach directly to the siphon tips. They penetrate the soft tissues using a piercing stylet apparatus on a long extendible proboscis and extract body fluids from their hosts. Large numbers (over 20 per siphon) may lead to tissue irritation and cessation of feeding by the clam host. No mortalities have been attributed to these snails to date.

Diagnostic techniques

Gross Observations: Small white snails less than 3 mm long attached to the siphon or mantle margins of clams.

Methods of control

No known methods of prevention or control. Recommend avoidance of introduction of infected clams into areas where these snails have not been previously recorded.


Harbo, R., N. McDaniel, D. Swanston and P. Lafollette. 2012. An exciting new discovery: the lightly-sculptured Odostome snail, Evalea tenuisculpta (Carpenter, 1864) feeding on the siphon tips of the fat gaper, Tresus capax (Gould, 1850) in Vancouver Harbour, British Columbia. The Dredgings 52(2): 3-4. (For the electronic version see tenuisculpta feeding on the siphon tips of the Fat Gaper, Tresus capax.pdf).

Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. In: O. Kinne (ed.). Diseases of Marine Animals. Volume II: Introduction, Bivalvia to Scaphopoda. Biologische Anstalt Helgoland, Hamburg, p. 797-800.

McGladdery, S.E., R.E. Drinnan and M.F. Stephenson. 1993. A Manual of the parasites, pests and diseases of Canadian Atlantic bivalves. Canadian Technical Report of Fisheries and Aquatic Sciences No. 1931, p. 90-91.

Citation Information

Bower, S.M. (2013): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Siphon Snails of Clams and Cockles.

Date last revised: May 2013
Comments to Susan Bower

Date modified: