LIFE-CYCLE OF ECHINOCHASMUS-MACROCAUDATUS N-SP (TREMATODA, ECHINOSTOMATIDAE)

The life-cycle of Echinochasmus macrocaudatus n. sp., from mother-spor ocyst to adult, was studied under natural and experimental conditions. The aquatic snails Pyrgophorus coronatus (Prosobranchia: Hydrobiidae) from cenotes (sinkholes) of the Yucatan Peninsula, Mexico, served as the first intermediate host of this parasite, liberating cercariae pos sessing an extremely large tail (zygocercous cercaria). Metacercariae of the fluke were encysted on the gills of the characid fish Astyanax fasciatus (natural infection); the poeciliids Xiphophorus variatus and Poecilia velifera were suitable experimental hosts. Feeding experimen ts with E. macrocaudatus metacercariae resulted in finding adult trema todes, possessing 22 collar spines (with 2 angle spines on each side), in the intestine of chicks and ducks. E. macrocaudatus differs from t he most closely related species, E. schwartzi Price, 1931, by its larg er oral sucker (138-170 x 118-176 mu m) and by the position of the ace tabulum which is situated at two-fifths of the body length.