Paramoeba invadens of Sea Urchins


Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Paramoeba invadens, Sea urchin paramoebiasis.

Scientific name or taxonomic affiliation

Paramoeba invadens.

Geographic distribution

Atlantic coast of Nova Scotia, Canada.

Host species

Strongylocentrotus droebachiensis.

Impact on the host

Infection causes muscle necrosis, general infiltration of coelomocytes, reddish-brown discolouration, and high mortalities. From 1980 to 1983 sea urchin mortalities were estimated at 245,000 tons. Following the depletion of the sea urchin population, seaweed abundance increased providing habitat for lobster recruitment. This may be one of the best examples of how a disease can affect ecosystem structure.

Diagnostic techniques

Gross Observations: Muscle degeneration in the tube feet, spines and mouth parts results in immobility, loss of attachment, cessation of feeding, and death.

Histology: Observation of Paramoeba invadens (20-35 µm long and 8-15 µm wide with digitiform pseudopodia) in tissue sections from diseased urchins. The parasome (2 to 3 µm in size) has Feulgen positive poles but no Feulgen positive central band and lies adjacent to the nucleus.

Culture: This amoeba was easily cultured on malt yeast and on non-nutrient agar with marine bacteria as a food source. There was some loss of virulence after 15 weeks in monoxenic culture (on a single strain of Pseudomonas nautica) and after 58 weeks in polyxenic culture (mixed marine bacteria).

Methods of control

No known methods of prevention or control. The infection is waterborne and transmission is direct; however, possible free-living habitat or other potential hosts are not known. Mortalities were not observed in other echinoderms including other echinoids, asteroids, and ophiuroids from the same area.


Jellett, J.F. and R.E. Scheibling. 1988. Virulence of Paramoeba invadens Jones (Amoebida, Paramoebidae) from monoxenic and polyxenic culture. Journal of Protozoology 35: 422-424.

Jellett, J.F., A.C. Wardlaw and R.E. Scheibling. 1988. Experimental infection of the echinoid Strongylocentrotus droebachiensis with Paramoeba invadens: quantitative changes in the coelomic fluid. Diseases of Aquatic Organisms 4: 149-157.

Jones, G.M. 1985. Paramoeba invadens n. sp. (Amoebida, Paramoebidae), a pathogenic amoeba from the sea urchin, Strongylocentrotus droebachiensis, in eastern Canada. Journal of Protozoology 32: 564-569.

Jones, G.M. and R.E. Scheibling. 1985. Paramoeba sp. (Amoebida, Paramoebidae) as the possible causative agent of sea urchin mass mortality in Nova Scotia. The Journal of Parasitology 71: 559-565.

Jones, G.M., A.J. Hebda, R.E. Scheibling and R.J. Miller. 1985. Histopathology of the disease causing mass mortalities of sea urchins (Strongylocentrotus droebachiensis) in Nova Scotia. Journal of Invertebrate Pathology 45: 260-271.

Miller, R.J. 1985. Succession in sea urchin and seaweed abundance in Nova Scotia, Canada. Marine Biology 84: 275-286.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Paramoeba invadens of Sea Urchins.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: