Polystomes of the world (Polystomatidae: Monogenea) : an appraisal of intestinal morphology and species diversity
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Species interact and exploit one another for a number of reasons, including transportation, shelter or nutrition such as in parasitic relationships. Parasitism is an important aspect in life and is common in all taxonomic groups. Parasites are often host-specific and can be endoparasites or ectoparasites. The phylum Platyhelminthes includes the class Monogenea or monogenetic parasitic flukes. Monogeneans are mainly parasitic in fish but the family Polystomatidae, also commonly referred to as polystomes, are found on the skin and gills of the Australian lungfish, tadpole gills, kidneys and urinary bladders of frogs, gills and skin of salamanders, cloaca and phalodeum of caecileans, on the eye, in the nose, mouth or urinary bladder of freshwater turtles and on the eye of the hippopotamus. Polystomes have a cosmopolitan distribution, and are found on all hospitable continents. Polystome species were first discovered in the 1758. Between 1961 and 1980 French researchers focussed on Central and West Africa and described a large number of parasites. Polystome discovery has steadily decreased in the last 30 years, however despite this, new species are still being discovered annually. The list of currently known polystomes is most likely only a small portion of the species that exists. Wherever scientists searched for polystomes, new species were discovered. The current distribution of polystomes is not at all a true reflection of their global distribution but merely an indication of research effort. Monogenean flatworms exhibit many variations in the morphology of the intestinal tract. These parasites display two distinct diets, where one group mainly feeds on blood while the other mainly feeds on mucus and epithelial tissues. Thus the feeding habits and other factors such as the shape of the caeca, the presence/absence and number of medial and lateral diverticula as well as anastomosis may play a role in the morphology of the intestinal tract, which can be used as a classification tool to classify polystome species into specific genera. The three aims of the study were to: * Conduct a literature study to compile a species list and source of information on all valid polystome taxa. * Review the intestine shape of all polystomes and evaluate it as a taxonomic characteristic. * Conduct a species description of a new North American chelonian polystome belonging to the genus Polystomoides.