Date of this Version
Journal of Oceanography and Marine Research (2014) 2(1): 117
Müller was the first to describe a monogenean, collected from the skin of the halibut (Hippoglossus hippoglossus). However, he regarded the parasite as a leech and named it Hirudo hippoglossi. It was not until 1858 that its status as a monogenean was established by van Beneden and named Epibdella (now Entobdella) hippoglossi. Van Beneden published a detailed and accurate description of the parasite and one of his excellent illustrations is reproduced here. Entobdella hippoglossi is one of the largest monogeneans, measuring up to 2 cm in length. It has a smaller relative, measuring 5 to 6 mm in length, which was described by van Beneden and Hesse in 1864 and named Phyllonella (now Entobdella) soleae from the skin of the Dover or common sole, Solea solea. This parasite is now perhaps the best known monogenean in terms of its biology.
The Phylum Platyhelminthes (flatworms) to which the Monogenea belongs is a major sub-division of the Animal Kingdom. Platyhelminths lack a skeleton and a blood system and are regarded as relatively simple on an evolutionary scale of anatomical development, just ‘ahead’ of sponges and cnidarians. Many flatworms are free-living but they also include three groups with parasitic life styles. Two of these, the Cestoda (tapeworms) and Digenea (flukes) parasitise the full range of vertebrates, from fishes to mammals, and have complex life cycles, with one or two intermediate hosts in addition to the main or definitive vertebrate host. Members of the third parasitic group, the Monogenea, are mostly restricted to the skin and gills of marine and freshwater fishes and have relatively simple life cycles, lacking intermediate hosts, new hosts being infected by tiny free-swimming ciliated larvae or oncomiracidia. Exceptions to this are the gyrodactylid monogeneans, most of which are viviparous (some are oviparous as are most monogeneans), giving birth to unciliated individuals similar in size to the parent. These parasites spread to new hosts by contagion, via the substrate as a staging post, by contact with detached drifting parasites or by contact between living fishes and infected dead fishes.
An outline classification of the Monogenea, showing the relationships of the families is available in Kearn, although aspects of this scheme are controversial.