The Biology Of Selected Freshwater Monogenectic Trematodes

The taxonomic history of monogenetic trematodes was begun by Rudolphi who, in 1808, was responsible for the order Trematodes. Van Beneden proposed the term monogeneses for trematodes which developed with metamorphosis and Digneses for those which developed with metamorphosis. The former generally contain ectoparasites whereas the latter consists of endoparasites. Carus proposed the terms lYlonogenea and Digenea to replace the terms of I/an Beneden in 1863. In 1892, lYlonticelli divided the order Trematoda into the suborders Heterocotylea, Aspidocotylea, and IYlalacocotylea. The suborders Heterocotylea coincides with the lYlonogenea. The Aspidocotylea and iYlalacocotylea are divisions of the Digenea. Odhner divided the lYlonogenea of Carus into Polypis thocotylea and (Ylonopisthocotylea, respectively, on the basis of the presence or absence of a genito-intestinal canal. According to Fuhrmann (1928), as set forth in Kukenthal\u27s Handbuch der Zoologie the lYlonogenea and Digenea of Carus are accepted as orders and the order Trematoda of Rudolphi is elevated to the status of class. The order lYlonogenea of Carus as given by Fuhrmann embraces three suborders, iYlonopisthodiscinea, lYlonopisthocotylinea and Polypisthocotylinea. Price (1937a) prefers the divisions lYlonopisthocotylea and Polypisthocotylea of Odhner as suborders to those Fuhrmann. The monogenetic trematodes are mostly ectoparasites that typically inhabit the gills and, occasionally the skin of freshwater and marine fishes. Bychowsky (19S7) states that many forms occur on all gill arches of bony and cartilaginous fishes. However, some forms prefer certain pairs of gill arches. Different species of monogenetic trematodes seem to have favorite places of location within the limits of a single gill arch. A few monogenetic trematodes occur on crustaceans and cephalopods. Some tend toward endoparasitism by going into structures that open to the exterior, such as the nasal and pharyngeal cavities, urinary bladder, and ureters of fishes, amphibians, and reptiles. Only one genus (Dictylocotyle) is known to inhabit the interior of the host and it is found in the coelom of a ray. The Monogenea move about on their host by looping in a leech-like manner, alternately attaching pro- and opisthaptors. They feed on slime, epithelial cells, and blood exuding from places damaged by their hooks and may seriously injure the gills of the host, especially in the case of young fish (Bychowsky, 1957)