Stichosomes occur in two orders of the Nematoda: Trichinellida, with at least
six families, and Mermithida, with two families. Recent phylogenetic analysis
based on a synthesis of molecular and morphological data suggest that the
stichosome may be an example of parallel evolution in the Trichinellida and
Mermithida (De Ley and Blaxter, 2002; Ferris, 2007).
The pharynx is narrow and thin-walled anteriorly and which, posteriorly, is
surrounded by unicellular, glandular stichocytes, each with a duct into the
The pharynx extends one-fourth to nine-tenths of the body length in various
taxa and is almost devoid of musculature. The region of the pharynx surrounded
by stichocytes isknown as the stichosome.
Contact with soil contaminated with eggs or larvae of nematode
parasites is a common form of transmission that results in human infection. The
nematodes can live for years as adults in the human intestinal tract. Soil
becomes contaminated by fecal material of infected humans and other animal
More than a billion people are infected with at least one species.
The most important nematode infections of the human gastrointestinal tract are
the intestinal roundworm (Ascaris
lumbricoides), whipworm (Trichuris trichiura), and
hookworm (Necator americanus or Ancylostoma
It is common for a single individual, especially a child living in a less
developed country, to be chronically infected with all three of the nematode
parasites, which results in malnutrition, stunted growth stunting, retarded
intellectual development, and cognitive and educational deficiencies.
Adult hookworms (Ancylostoma
duodenale and Necator americanus)
parasitize the upper part of the human small intestine, whereas
Ascaris lumbricoides parasitize the entire
small intestine and adult
Trichuris trichiura live in the large intestine, especially the caecum.
The parasites can live for several years in the human
gastrointestinal tract. After mating, each adult female produces thousands of
eggs per day which leave the body in the feces.
Dictionary of Terminology
De Ley, P. and Blaxter, M. 2002. Systematic position and
phylogeny. Pp 1-30 in Lee, D.L. (ed.). The Biology of Nematodes. Taylor and
Francis, London and NY. 635p.
Lee, D.L. 2002. Life cycles. Pp 61-72 in Lee, D.L. (ed.). The
Biology of Nematodes.Taylor and Francis, London and NY. 635p.
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