Redia and cercaria
A single large redia positioned next to a single cercaria (bottom, with forked tail). These are both larval stages of flukes (phylum Platyhelminthes, class Trematoda). Redia are typically found in snails, and they asexually produce cercaria (which can be seen inside the redia as all the individual balls). Cercaria typically leave the snails and hunt the next host in the life cycle, such as a fish (for the human liver fluke) or another human (for Schistosoma).
Copyright © 2011 Marc Perkins