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Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, commonly known as tapeworms.
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts . The intermediate host, in which asexual reproduction occurs, is usually a snail .
Nematodes are very small, slender worms. Most are free-living, often less than 2.5 mm long and some only about 1 mm. Many nematodes are microscopic. Some soil nematodes can reach up to 7 mm in length, and some marine species can reach up to 5 cm. Some are parasitic and can reach lengths of 50 cm or more. [42]
Telorchis is a genus of trematode parasites found in many herps, comprising around 70 species. [2] This parasite is an indirect parasite, with a snail intermediate host and a reptile or amphibian definitive host.
Trematodiasis is a group of parasitic infections caused by different species of flukes, in humans mainly by digenean trematodes. [4] Symptoms can range from mild to severe depending on the species, number and location of trematodes in the infected organism. [1]
[16] [17] Helminth eggs of concern in wastewater used for irrigation have a size between 20 and 90 μm and a relative density of 1.06–1.23. [18] It is very difficult to inactivate helminth eggs, unless temperature is increased above 40 °C or moisture is reduced to less than 5%. [ 18 ]
[20] [21] However, a 2007 study concluded that Acoela and Nemertodermatida were two distinct groups of bilaterians. [ 22 ] Xenoturbella , a bilaterian whose only well-defined organ is a statocyst , was originally classified as a "primitive turbellarian". [ 23 ]
Some internal fish parasites are spectacular, such as the philometrid nematode Philometra fasciati which is parasitic in the ovary of female Blacktip grouper; [14] the adult female parasite is a red worm which can reach up to 40 centimetres in length, for a diameter of only 1.6 millimetre; the males are tiny.