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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]
Demodex folliculorum is a microscopic mite that can survive only on the skin of humans. [2] [3] Most people have D. folliculorum on their skin.Usually, the mites do not cause any harm, so are considered an example of commensalism rather than parasitism; [4] but they can cause disease, known as demodicosis.
Worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms); [1] 6.7 metres (22 ft) for the African giant earthworm, Microchaetus rappi; [2] and 58 metres (190 ft) for the marine nemertean worm (bootlace worm), Lineus longissimus. [3]
Worms commonly live for about one year, [5] during which time females can lay up to 20,000 eggs per day. Recent studies using genome-wide scanning revealed that two quantitative trait loci on chromosome 9 and chromosome 18 may be responsible for a genetic predisposition or susceptibility to infection of T. trichiura by some individuals.
Oligochaetes are well-segmented worms and most have a spacious body cavity (coelom) used as a hydroskeleton.They range in length from less than 0.5 mm (0.02 in) up to 2 to 3 metres (6.6 to 9.8 ft) in the 'giant' species such as the giant Gippsland earthworm (Megascolides australis) and the Mekong worm (Amynthas mekongianus).
The microscopic mite Lorryia formosa (). The mites are not a defined taxon, but is used for two distinct groups of arachnids, the Acariformes and the Parasitiformes.The phylogeny of the Acari has been relatively little studied, but molecular information from ribosomal DNA is being extensively used to understand relationships between groups.
Ascaris lumbricoides is a large parasitic roundworm of the genus Ascaris. It is the most common parasitic worm in humans. [1] An estimated 807 million–1.2 billion people are infected with Ascaris lumbricoides worldwide. [2]
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. Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed ...