Escape of rediae from miracidia of Philophthalmus megalurus and Philophthalmus gralli during in vitro culture

Miracidia of the eyeflukes Philophthalmus megalurus and Philophthalmus gralli contain a preformed larval stage that was identified as a redia by electron microscopy and, on living forms, by the presence of ambulatory buds and an oral opening. This redial stage escaped and actively moved about when the miracidium stopped swimming in pond water. No redial escape was observed in NaCl solutions even though miracidia became immobile, but escape was noted in Hanks' balanced salt solution (HBSS) after 7 hr of exposure. When miracidia were placed in RPMI-1640 and Eagle's minimum essential medium, rediae escaped much earlier than in pond water and HBSS. Redial escape in vitro will provide a good source of material to initiate cultures of this larval stage.