The occurrence of Corynosoma strumosum in the grey seal, Halichoerus grypus, caught off the Atlantic coast of Ireland.

The occurrence, location and sex ratio of Corynosoma strumosum (Acanthoceophala: Polymorphidae) from 26 juvenile grey seals, Halichoerus grypus, by-caught from around the Inishkea Islands, Co. Mayo, from March to June 1997 were recorded. The location of C. strumosum within the seal did not vary, with all worms being found in the small intestine. The prevalence of infection was 100%, with no other acanthocephalan species being recorded. The mean abundance was 416 (range 80-846) C. strumosum per seal. There was no significant change in abundance by month. The sex ratio of mature female to mature male parasites was 1.2:1. The lengths of female and male worms did not differ significantly.