Invasion and development strategies of Ichthyophthirius multifiliis, a parasitic ciliate of fish.

Like many other parasites, Ichthyophthirius multifliis faces critical changes when moving between free-living and parasitic phases. This ciliate alternates between feeding in the epithelium of freshwater fishes and swimming and encysting in fresh water. Several organelles appear to play key roles in successful negotiation o f these changes. Margaret Ewing and Katherine Kocan discuss a variety of cellular components important in host invasion and development of the parasite, with particular attention given to mucocysts, extrusive organelles whose secretions appear to be essential to both life cycle phase changes.