Pseudocorynosoma constrictum is an acanthocephalan parasite of North American waterfowl. Eggs are released into lakes, where they are ingested by the first host, amphipods. After about a month of development, the infective cystacanth stage is reached and the worm can be transmitted to birds. The cystacanths are bright orange and clearly visible through the cuticle of the intermediate host (see picture). Several acanthocephalan species have orange cystacanths, and there has been much debate about the function of this pigmentation. Hypotheses include increased conspicuousness to final host predators, protection against UV radiation, or that it is just a byproduct of larval physiology.
Contributed by Daniel Benesh.