Cercaria larva (video). Upper Newport Bay, Newport Beach, Orange County, CA. 5/4/13. © Peter J. Bryant.


Phylum Platyhelminthes; Family Cyathocotylidae

Species unknown, but almost certainly a trematode in the family Cyathocotylidae, the marine species of which have a complex life cycle involving three hosts. It is probably Mesostephanus appendiculatus, which uses the California Horn Snail, Cerithidea californica as its first intermediate host. The parasite develops in the snail host to produce the free-swimming cercaria shown here. The cercaria penetrate the skin of small fish (probably killifish) and encyst in the muscles. When the fish is eaten by a bird, the adult trematode is parasitic in the digestive tract. The adults produce eggs that are passed in the feces. On exposure to water, the eggs hatch and liberate a ciliated miracidium that infects the snail and develops to the cercaria stage. See Parasites as Indicators of Coastal Wetland Health.

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(Click for Video)
. Larvae removed from a California Horn Snail, Cerithidea californica. Upper Newport Bay, Newport Beach, Orange County, CA. 05/28/13. © Peter J. Bryant