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Free-living flatworms are mostly predators, and live in water or in shaded, humid terrestrial environments, such as leaf litter. Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts.
Unlike the flatworms, nematodes have a tubular digestive system, with openings at both ends. Like tardigrades, they have a reduced number of Hox genes , but their sister phylum Nematomorpha has kept the ancestral protostome Hox genotype, which shows that the reduction has occurred within the nematode phylum.
Helminths of importance in the sanitation field are the human parasites, and are classified as Nemathelminthes (nematodes) and Platyhelminthes, depending on whether they possess a round or flattened body, respectively. [8] Ringworm (dermatophytosis) is actually caused by various fungi, and not by a parasitic worm. [11] [12]
The position of the Cestoda within the Platyhelminthes and other Spiralian phyla based on genomic analysis is shown in the phylogenetic tree. The non-parasitic flatworms, traditionally grouped as the "Turbellaria", are paraphyletic, as the parasitic Neodermata including the Cestoda arose within that grouping. The approximate times when major ...
Platyhelminthes (flatworms) form another worm phylum which includes a class Cestoda of parasitic tapeworms. The marine tapeworm Polygonoporus giganticus, found in the gut of sperm whales, can grow to over 30 m (100 ft). [44] [45] Nematodes (roundworms) constitute a further worm phylum with tubular digestive systems and an opening at both ends.
Liver fluke is a collective name of a polyphyletic group of parasitic trematodes under the phylum Platyhelminthes. [1] They are principally parasites of the liver of various mammals, including humans. Capable of moving along the blood circulation, they can occur also in bile ducts, gallbladder, and liver parenchyma. In these organs, they ...
An example of a marine worm, the Parborlasia corrugatus lives at depths of up to 4,000 metres.. Any worm that lives in a marine environment is considered a water worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida (segmented worms), Chaetognatha, Hemichordata, and Phoronida.
Trematoda is a class of flatworms known as flukes or trematodes. [1] They are obligate internal parasites with a complex life cycle requiring at least two hosts.The intermediate host, in which asexual reproduction occurs, are mollusks and usually a snail.