The morphology and evolution of Tristoma adcoccineum (Monogenea: Capsalidae) from the swordfish (Xiphias gladius) from the N.W. Hawaiian Islands

The gills of 53 swordfish (Xiphias gladius) collected during January of 1990 were examined for monogenetic trematodes of the genus Tristoma. All swordfish examined were infected with Tristoma adcoccineum (53) and 24 percent (12) were also found to be infected with T. integrum. Scanning electron microscope analysis of the dorsal marginal comb teeth rows of T. adcoccineum indicate that these structures are not uniform in shape and may serve different functions. The saw-like anterior teeth may be used as feeding or rasping and the spike-like posterior teeth may be used for attachment. Analysis of the number of comb teeth rows versus the sexual maturity of the parasite indicated a significant relationship, with numbers of comb teeth rows increasing with sexual maturity. Phylogenetic analysis of the genus Tristoma indicates that T. adcoccineum is most closely related to T. coccineum and may have diverged about 3.5 million years ago.