The life cycle of Euclinostomum heterostomum (Rudolphi, 1809) (Trematoda: Clinostomatidae)

In small forest streams of West Nigeria the snail species Bulinus globosus was found to be the first intermediate host of a clinostomatid species which proved in successful infection experiments with the cichlid fish Tilapia zillii as second intermediate host to be Euclinostomum heterostomum (Rudolphi, 1809). Final hosts are herons. The morphology of the redia and the morphology and behaviour of the cercaria are described for the first time. The metacercaria which settles dorsal to the swim-bladder or in the kidney of the host fish requires more than two months (at tropical temperatures) for full development. Histological sections of the metacercaria revealed that its pharynx is provided with only few muscle fibres but surrounded by many myoblast-like cells, and the fact that the interior surface of this organ has a dense brush-like lining consisting of long microtriches. The pathology of infected fish is briefly described, and remarks about the geographical distribution of the parasite are given.