noun, plural: trematodes
Phylum Platyhelminthes, commonly called flatworms, is comprised of four groups: (1) turbellarians, (2) trematodes, (3) monogeneans, and (4) cestodes. They are characterized by their flattened, bilaterally symmetrical body.
The trematodes are distinguished by their holdfasts resembling suckers that aid them to anchor within the host. Most of them are parasites of mollusks and vertebrates. They include two subclasses: Digenea and Aspidogastrea. The subclass Digenea includes most of the trematodes that live as obligate parasites of both mollusks and vertebrates. The subclass Aspidogastrea includes trematode species that live as obligate parasites of mollusks but may also infect vertebrates, such as turtles and fish.
The trematodes are also called flukes. Based on the system of the vertebrate host that they infect, they are classified into tissue flukes or blood flukes. The tissue flukes, e.g. Paragonimus westermani, Fasciola hepatica, and Clonorchis sinensis, are those that are found in lungs, bile ducts, and other tissues of their hosts. The blood flukes, e.g. Schistosoma, are those that occur in the blood of their vertebrate host. Humans may also serve as a host to certain trematodes, such as Schistosoma, Clonorchis, Opisthorchis, Fasciola, and Paragonimus species.
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