Nematomorph Parasitism of Crabs


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Parasitic juvenile nematomorphs in crabs.

Scientific name or taxonomic affiliation

Nectonema spp. (Nematomorpha: Nectonematoidea)

Geographic distribution

Bay of Fundy in eastern Canada and various coastal waters of the world where parasitic juveniles have been reported from crustaceans and free-swimming adults have been encountered.

Host species

Cancer borealis, Cancer irroratus, Pagurus acadianus, and other species of brachyuran and anomuran crabs and shrimp.

Impact on the host

Juveniles nematomorphs up to about 1 m in length, but usually less than 1.5 mm in diameter inhabit the body cavity. The size of individual Nectonema appears to be related to the size of individuals of the host species. Although there is little to no apparent tissue damage in most cases, evidence of gonad degeneration occurred in a few parasitized male C. irroratus. The route of infection is not known but it is suspected that on maturation of the nematomorph, natatory bristles develop and the "worm" exits the host by penetrating the membrane between the posterior margin of the cephalothorax and abdomen. The life expectancy of infected crustaceans is not known.

Diagnostic techniques

Gross Observations: White to creamy yellow thin worm-like organisms usually coiled in the posterior region of the haemocoel or along the hepatopancreas.

Methods of control

No known methods of prevention or control.


Leslie, H.A., A. Campbell and G.R. Daborn. 1981. Nectonema (Nematomorpha: Nectonematoidea) a parasite of decapod Crustacea in the Bay of Fundy. Canadian Journal of Zoology 59: 1193-1196.

Citation Information

Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Nematomorph Parasitism of Crabs.

Date last revised: September 1996
Comments to Susan Bower

Date modified: