The isopod parasites of South American fishes.
Most isopod parasites belong to the family Cymothoidae but the family Excorallanidae is also represented. In South American waters, there are 18 species in eight genera known from marine fishes, and 28 species in 12 genera known from freshwater fishes. South America has more freshwater cymothoids than any other continent in the world. Diagnoses of the genera are provided, along with measurements, host data, and geographic distribution for each species. The parasitic isopods are found on the skin, in the mouth (over the tongue), in the branchial chamber, and within the peritoneal cavity of their hosts. Most are highly host-specific but some, especially the skin dwellers, have been found on a wide variety of host species. Differences in the morphology of the mouthparts of freshwater and marine cymothoids are discussed. The two groups appear to be phylogenetically distinct at the subfamily level. The feeding habits and pathogenicity of these isopods are also discussed.