Abstract
Monogeneans, a fully-fledged class of the Platyhelminth phylum, are represented by thousands of species, ectoparasites of aquatic vertebrates. Marine Teleosts are parasitized by the greatest number of them. These organisms arouse fundamental as well as applied questions, most of them tackled during the last decades by Louis Euzet and several of its colleagues of Montpellier. A synthesis of these ecological works is presented here, as some recent reflections relative to their population dynamics.