The life-history ofMesorchis denticulatus (Rudolphi, 1802) Dietz, 1909 (Trematoda,Echinostomatidae)

Red-tailed gigantocercous cercariae which developed in the euryhaline snailHydrobia ulvae Pennant (Prosobranchia, Hydrobiidae) in Denmark developed intoMesorchis denticulatus (Rudolphi 1802) Dietz 1909 (Echinostomatidae). Synonyms areStephanoprora denticulata (Rudolphi 1802) Odhner 1910,M. pseudoechinatus (Olsson 1876) Dietz 1909, andS. pseudoechinata (Olsson 1876) Odhner 1910. The rediae are cannibals devouring whole extraredial cercariae. The cercariae are actively ingested by small fish or carried by the respiratory current into their gill chambers. They encyst in the gill filaments.Gasterosteus aculeatus L.,Pungitius pungitius L. andPomatoschistus microps Krøyer are the most important second intermediate hosts in Danish waters, but all species of small fish, exceptAnguilla anguilla L., exposed to the cercariae were experimentally infected. Chickens were suitable laboratory hosts, whereasLarus spp. and other piscivorous birds function as natural final hosts in Europe and North America. Mammals may also be suitable hosts.