Mussel Gill Turbellaria


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Mussel gill flatworms.

Scientific name or taxonomic affiliation

Urastoma cyprinae (synonymized with Urastoma evelinae) and possibly other species of Turbellaria. Another species of turbellaria (Paravortex-like) was reported as a symbiont in the intestinal lumen of less than 3% of Mytilus galloprovincialis from Galicia, Spain (Villalba et al. 1997).

Geographic distribution

Specific reports in mussels from the coast of Galicia in NW Spain, Portugal, the Mediterranean Sea and the Black Sea but U. cyprinae has been observed in other bivalves or found free-living in Australia, Brazil, North Atlantic, and the east coast of North America but not observed in Canada.

Host species

Mytilus galloprovincialis, Mytilus edulis and other bivalves including oysters, clams and scallops.

Impact on the host

In Europe, U. cyprinae is reported as an opportunistic mantle inhabitant on the gills of bivalves, or free-living on muddy bottoms. Although not yet associated with mussel mortalities, U. cyprinae can cause disorganization of the gill filaments (including reduction of space between the lamellae and increase in the size of haemal sinuses within the lamellae), a heavy infiltration of haemocytes and subsequent necrosis of adjacent gill tissue. Robledo et al. (1994) suspected that flatworms could greatly reduce feeding capacity in heavily infected mussels.

Diagnostic techniques

Gross Observations: Small oval or pyriform, white or light coloured spots (1.6 ± 0.4 by 1.0 ± 0.4 mm) containing up to 5 flatworms located between gill lamellae. Immature live U. cyprinae from mussels in Galicia varied between 0.4 and 0.8 mm in length and had two pigmented eyes near the anterior end. Although most frequently found in the middle area of the four demibranchs, they occurred over the entire gill surface and were detected swimming freely in the pallial cavity.

Whole Mounts: For species confirmation, stain with acetic acid alum carmine and mount in permount. Larger specimens can be imbedded in paraffin for sectioning as necessary.

Histology: Examine transverse sections though gill and palp area of mussels for cross-sections through turbellarians characterised by ciliated surfaces. In severely affected areas, histopathology as mentioned above may be observed.

Methods of control

No known methods of prevention or control. Greater numbers of U. cyprinae occurred in mussels inhabiting a silty bottom than in cultivated mussels suspended above the bottom. This turbellarian was also most numerous in mussels during the colder seasons of the year. Although not currently considered to be a health or marketing problem, it could be considered a potential threat to mussel culture in some areas. Thus, managers in areas currently free of these flatworms should prevent their introduction.


Cannon, L. R. G. 1986. Turbellaria of the World - A Guide to Families and Genera. Queensland Museum, Australia. 132 p.

Murina, G.V. and A.I. Solonchenko. 1991. Commensals of Mytilus galloprovincialis in the Black Sea: Urastoma cyprinae (Turbellaria) and Polydora ciliata (Polychaeta). Hydrobiologia 227: 385-387.

Noury-Sraïri, N., J.-L. Justine and L. Euzet. 1990. Ultrastructure of the tegument and subepithelial glands of Urastoma cyprinae prolecithophora turbellarian parasite of molluscs. Annales des Sciences Naturelles Zoologie et Biologie Animale 11: 53-71. (In French).

Robledo, J.A.F., J.C. Ráceres-Martínez, R. Sluys and A. Figueras. 1994. The parasitic turbellarian Urastoma cyprinae (Platyhelminthes: Urastomidae) from blue mussel Mytilus galloprovincialis in Spain: occurrence and pathology. Diseases of Aquatic Organisms 18: 203-210.

Trotti, G.C, E.M. Baccarani, S. Giannetto, A. Giuffrida and F. Paesanti. 1998. Prevalence of Mytilicola intestinalis (Copepoda: Mytilicolidae) and Urastoma cyprinae (Turbellaria: Hypotrichinidae) in marketable mussels Mytilus galloprovincialis in Italy. Diseases of Aquatic Organisms 32: 145-149.

Villalba, A., S.G. Mourelle, M.J. Carballal and C. López. 1997. Symbionts and diseases of farmed mussels Mytilus galloprovincialis throughout the culture process in the Rías of Galicia (NW Spain). Diseases of Aquatic Organisms 31: 127-139.

Citation Information

Bower, S.M. (2001): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Mussel Gill Turbellaria.

Date last revised: June 2001
Comments to Susan Bower

Date modified: