Metacercárias livres de diplostomídeos (Digenea, Diplostomidae) em Loricariichthys anus (Val., 1840) (Siluriformes, Loricariidae) do estado do Rio Grande do Sul, Brasil

free (unencysted) metacercariae of an undetermined species of digenetic trematode (diplostomidae) were found over and in the kidney ducts, over the liver, over the peritoneum, in the abdominal cavity and in the brain, but not in the eyes of mailed catfishes, loricariichthys anus, captured in the coastal lagoons of peixoto and pinguela, osório, rs; in the channel linking the lagoons, imbé, rs, and in the jacui river, porto alegre, rs, southern brazil. the morphology of the metacercariae is described and pictured. they are differentiated from diplostomum (a.) compactum and d. (a.) mardox for having an acetabulum, being identified, at present, as an undetermined species of the genus diplostomum. the metacercariae recorded in the present study are also compared with the strigeatoid metacercariae described parasitizing subtropical fishes in argentina, looking similar to those metacercariae described as tylodelphylus cardiophilus from the pericardial cavity of the "peixe-rei"