RESUMEN
Coccidian oocysts were proved to be found in 70 of 100 collected Pirenella conica snails, with a natural infection of 70%. It was observed that, Pfeifferinella sp. was transferred between hepatopancreas and small intestine of snail. The prepatent period of Pfeifferinella sp. infecting P. conica snails ranged from 14-18 days and the patent period was reached 50 days [P.L]- Mer-ogony stages were the early stages observed in this study. These stages were observed in the hepatopancreas and in a large clear parasiteophorous vacuole [PV]. In snails killed 4 days P.I. immature meronts were measured 12x10 microm containing 8 nuclei. Meanwhile, mature meronts with about 6 differentiated merozoites were detected as early as 6 days P.I., and measured 3.1xl.4jim. The earliest gametogonic stages were seen in the intestine of Pirenella conica snails killed 12 days P.L Microgamonts contained about 4 nuclei and measured 79x6.7microm. The mac-rogamonts measured 7.3x5.6|