Shell-boring Polychaetes of Scallops


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Shell-boring polychaetes.

Scientific name or taxonomic affiliation

Polydora spp. and Dodecaceria concharum.

Geographic distribution

Ubiquitous, although some species probably have limited distributions.

Host species

Patinopecten yessoensis, Crassedoma giganteum, Placopecten magellanicus, and various other species of bivalves that live on the surface of the substrate including oysters, mussels and abalone.

Impact on the host

Most infections are innocuous and of low intensity with the burrow being confined to the shell. However, in British Columbia, stunting, abnormally thickened shells and high mortalities caused by high intensities (burrows too numerous and interwoven to count in shells of dead scallops) of P. websteri have precluded the culture of introduced P. yessoensis in a few localities (Bower, 1990). In Japan, Mori et al. (1985) suggested that Polydora may have an adverse affect on the growth of Japanese scallops in some areas. Also, thickening of the shell (3-4 fold) by the scallop to prevent the polychaete from penetrating through the shell to living tissue may reduce swimming capacity of the scallop, thereby making it more accessible to predators (i.e. sea stars). In P. magellanicus perforation of the shell may lead to infiltration of mud (used by the polychaetes to line their tunnels) and formation of mud blisters on the inner surface of the shell surface. These blisters may occupy a large proportion of the mantle cavity space, but do not appear to adversely affect the scallop unless the blister impedes adductor muscle attachment.

Diagnostic techniques

Gross Observations: Hold clean shell against a bright light and examine through the shell matrix for sinuous burrows about 2 mm in diameter. Some Polydora sp. line their tunnels with mud and chronic incursion of mud into the extrapallial cavity can result in grossly visible mud blisters in P. magellanicus.

Wet Mounts: The polychaete must be removed from the shell intact for specific identification. Break the shell along the burrow using bone shears. Submerge the shell fragments in cool sea water and extract the intact living polychaete from the burrow with fine forceps and needle. Place the worm on a piece of plasticine and, using pins positioned along the edges of the body to keep the worm straight, flood with 70% alcohol and store in 50-70% isopropyl alcohol.

Note: these procedures are very labourious and time-consuming. For other techniques see Knudsen (1966).

Methods of control

Prevalence and intensity of infection can be reduced by avoiding localities with high intensities of P. websteri for the culture of scallops and by culturing the scallops off-bottom in other areas.


Ball, M.C. and S.E. McGladdery. 2001. Scallop parasites, pests and diseases: implications for aquaculture development in Canada. Bulletin of the Aquaculture Association of Canada 101-3: 13-18.

Bower, S.M. 1990. Shellfish diseases on the west coast of Canada. Bulletin of the Aquaculture Association of Canada 90: 19­22.

Bower, S.M. and G.R. Meyer. 1994. Causes of mortalities among cultured Japanese scallops, Patinopecten yessoensis, in British Columbia, Canada. In: Bourne, N.F., B.L. Bunting and L.D. Townsend (eds.). Proceedings of the 9th International Pectinid Workshop, Nanaimo, B.C., Canada, April 22-27, 1993. Volume 1. Canadian Technical Report of Fisheries and Aquatic Sciences 1994: 85-94.

Getchell, R.G. 1991. Diseases and parasites of scallops. In: S.E. Shumway (ed.). Scallops: Biology, Ecology and Aquaculture. Developments in Aquaculture and Fisheries Science No. 21. Elsevier Press, p. 471-494.

Knudsen, J.W. 1966. Biological Techniques - Collecting, Preserving, and Illustrating Plants and Animals. Harper and Row, New York. p. 157-160.

Kurochkin, Y.V., E.M. Tsimbalyuk and A.V. Rybakov. 1986. Parazitî i bolyezni. (Parasites and diseases.). In: P.A. Motavkin (ed.). Primorskii grebeshok. (The Yezo scallop or Japanese common scallop Mizuhopecten yessoensis (Jay).) Institute of Marine Biology, Far East Science Centre, Academy of the USSR, Vladivostok, p. 174­182. (In Russian).

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. 805-817.

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. 29-31.

Mori, K., Sato, W., Nomura, T. and Imajima, M. 1985. Infestation of the Japanese scallop Patinopecten yessoensis by the boring polychaetes, Polydora, on the Okhotsk Sea coast of Hokkaido, especially in Abashiri waters. Bulletin of the Japanese Society of Scientific Fisheries 51: 371­380. (In Japanese, with English abstract).

Citation Information

Bower, S.M., McGladdery, S.E. (2004): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Shell-boring Polychaetes of Scallops.

Date last revised: December 2004
Comments to Susan Bower

Date modified: