Trematode Metacercariae of Clams and Cockles


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Metacercarial infection of clams.

Scientific name or taxonomic affiliation

Various species in the Digenea families Bucephalidae, Sanguinicolidae, Monorchiidae, Fellodistomidae, Gymnophallidae, Lepocreadiidae, Zoogonidae, Echinostomatidae, Psilostomatidae, and Renicolidae.

Geographic distribution

Global, although each species probably has a confined distribution.

Host species

Venerupis (=Tapes) philippinarum, Tapes decussatus, Tapes aureus, Mya arenaria, Mercenaria mercenaria, Cardium glaucum, Cardium tuberculatum, Cerastoderma (=Cardium) edule, Abra ovata, Scrobicularia plana, Loripes lacteus, Divaricella divaricata, Venus gallina, Dosinia lupinus, Mactra corallina, Tellina tenuis, Lentidium mediterraneum, Donax trunculus, Donax semistriatus, Spisula subtruncata, Solen marginatus, Macoma baltica, Macoma inconspicua, Ensis siliqua, Darina solenoides, Gaimardia trapesina and Amiantis purpurata as well as various other bivalves including oysters and mussels.

Impact on the host

Majority of species are innocuous. However, some species in some clams are reported to cause abnormal clam behaviour (e.g., Parvatrema affinis can cause disorientation in M. baltica in Holland), severe tissue damage and eventual mortalities when in high intensities (e.g., Cercaria cerastodermae I. in C. edule in Sweden), castration (e.g., monorchiid cercariae caused lack of gamete production in 81% of infected Amiantis purpurata on the coast of Argentina), mantle-shell complex reactions involving hyperplasia and metaplasia of the mantle epithelium and calcium carbonate deposits to form partial coverings over the metacercaria (e.g., unidentified species of Gymnophallidae in Gaimardia trapesina from Argentina and Magellan Strait), shell deformities (e.g., Gymnophallus fossarum in various species of clams in Europe) and possibly pearls (e.g., Bartolius pierrei induced mineral concretions in Darina solenoides in Argentina). Sporocycts containing many cercaria (identified as Cercaria tapidis) were reported from the gonadal tissue of 9.7% of the Manila clams, V. philippinarum, in coastal areas of Korea (Lee et al. 2001) and in 12% of the same species of clam from Jeju, an island off the south coast of Korea (Nago and Choi 2004) with associated castration and deterioration of connective tissue adjacent to the sporocysts. No pathology has been associated with the various species of trematodes (all metacercarial stages) that occur in clams from Canada.

Diagnostic techniques

Squash Preparations: Thin slices (about 3 mm thick) of the clam body pressed between two plexiglass plates and examined under a dissecting microscope (50 ×) show metacercariae.

Histology: Cross sections of metacercariae and sporocysts (possibly containing developing cercaria) can be observed within the tissues.

Methods of control

Prevention and control impractical.


Bower, S.M., J. Blackbourn and G.R. Meyer. 1992. Parasite and symbiont fauna of Japanese littlenecks, Tapes philippinarum (Adams and Reeve, 1850), in British Columbia. Journal of Shellfish Research 11: 13-19.

Carballal, M.J., D. Iglesias, J. Santamarina, B. Ferro-Soto and A. Villalba. 2001. Parasites and pathologic conditions of the cockle Cerastoderma edule populations of the coast of Galicia (NW Spain). Journal of Invertebrate Pathology 78: 87-97.

Ching, H.L. 1965. Life cycles of Lacunovermis conspicuus n. gen., n. sp. and Meiogymnophallus multigemmulus n. gen., n. sp. (Gymnophallidae: Trematoda) from Macoma inconspicua and diving ducks from Vancouver, Canada. Proceedings of the Helminthological Society of Washington 32: 53-63.

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Cremonte, F., M.A. Kroeck and S.R. Martorelli. 2001. A new monorchiid cercaria (Digenea) parasitising the purple clam Amiantis purpurata (Bivalvia: Veneridae) in the Southwest Atlantic Ocean, with notes on its gonadal effect. Folia Parasitologica 48: 217-223.

Ituarte, C.F., F. Cremonte and G. Deferrari. 2001. Mantle-shell complex reactions elicited by digenean metacercariae in Gaimardia trapesina (Bivalvia: Gaimardiidae) from the Southwestern Atlantic Ocean and Magellan Strait. Diseases of Aquatic Organisms 48: 47-56.

James, B.L. and E.A. Bowers. 1967. The effects of parasitism by the daughter sporocyst of Cercaria bucephalopsis haimaena Lacaze-Duthiers, 1854, on the digestive tubules of the cockle, Cardium edule L. Parasitology 57: 67-77.

Jonsson, P.R. and C. André. 1992. Mass mortality of the bivalve Cerastoderma edule on the Swedish west coast caused by infestation with the digenean trematode Cercaria cerastodermae I. Ophelia 36: 151-157.

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Lee, M.-K., B.-Y. Cho, S.-J. Lee, J.-Y. Kang, H.D. Jeong, S.H. Huh and M.-D. Huh. 2001. Histopathologucal lesions of Manila clam, Tapes philippinarum, from Hadong and Namhae coastal areas of Korea. Aquaculture 201: 199-209.

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. 88-89.

Ngo, T.T.T. and K.-S. Choi. 2004. Seasonal changes of Perkinsus and Cercaria infections in the Manila clam Ruditapes philippinarum from Jeju, Korea. Aquaculture 239: 57-68.

Pekkarinen, M. and H.L. Ching. 1994. Comparisons of gymnophallid digeneans from north Pacific and Baltic clams, Macoma balthica (Bivalvia). The Journal of Parasitology 80: 630-636.

Citation Information

Bower, S.M. (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Trematode Metacercariae of Clams and Cockles.

Date last revised: February 2007
Comments to Susan Bower

Date modified: