Trematode infections in Pirenella conica in three sites of a mangrove lagoon in Sinai.

Over a period of 11 months, eight samples of Pirenella conica were taken at each of three sites of a mangrove lagoon in Sinai. Infection with larval trematodes, especially of Heterophyidae, was highest at the site within the mangrove thicket with a breeding colony of reef herons, the supposed definitive hosts of the Heterophyidae. The lowest frequency of infection was recorded from a tide-pool on the broad sand-flats surrounding the lagoon, where there was a great variation in the abundance of snails and xiphidiocercariae were more common than heterophyid cercariae. Predation from fish or other molluscs did not appear to be an important factor at either of these two sites. In all three sites, double infections of Heterophyidae and trematodes with xiphidiocercariae as well as of Heterophyidae and Echinostomatidae occurred less frequently than theoretically expected, but there was no competitive exclusion between Echinostomatidae and xiphidiocercariae.