AN OBSERVATION ON INTRACAPSULAR AND POST-EMBRYONIC PHASES OF RIVER NERITE (Theodoxus fluviatilis)

The river nerite (Theodoxus fluviatilis, Linnaeus, 1758) is one of the most common gastropod grazer species in Europe inland and brackish waters. Its feeding activity significantly impacts on periphyton which has a decisive role on the water parameters and the population dynamics. In the present study, reproductive outputs and larval phases of the river nerites were examined via field collected and laboratory cultivated samplings. The length of capsules laid by adults was between 0.7 and 1.1 mm. Viable embryos were detected first on the 33rd day post-spawning. After few development phases embryo reached a ready-to-hatch phase with comple-tely developed foot and pigmented protoconch before hatching. There was never more than one embryo per capsule. The earliest hatching was observed on the 53rd day of spawning. But most of the embryos did not hatch even they were fully developed. The shell length of the hatchlings was about 0.8 and the width was 0.6 mm. It was estimated that the length of a newly hatched crawling juvenile can be about 1/7 of the length of an adult.