cercar

noun
  1. A cercar is the larval form of certain parasitic flatworms, specifically trematodes, which are characterized by a tail that aids in swimming. These larvae are typically released from an intermediate host, such as a snail, and seek out a definitive host to continue their life cycle. noun
    The cercariae were released from the snail and swam in search of a new host.
    Researchers observed the cercariae under a microscope to study their movement.