Monogenea

Abstract

A large group of flatworms (Platyhelminthes) that are usually ectoparasitic (living on the exterior of the host). The Monogenea comprise a few thousand described species and probably many thousands of not yet described species. The vast majority of species is found on the gills, skin, and fins of fishes (elasmobranchs and teleosts), whereas some are found hi the mouth cavity and urinary bladder of turtles and frogs. A few species have secondarily become endoparasitic (living inside the host) in fishes, and a few infect marine cephalopods. They range in length from about 0.1 mm (0.004 in.) to several centimeters.