The order consists of two families: Mermithidae and Tetradonematidae. Mermithida are characterized by a stichosome
Most species are endoparasites of arthropods
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 pharyngeal lumen.
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 is
known as the stichosome.
In Romanomermis culicivorax, the preparasitic larva is equipped with a stylet which allows penetration through the cuticle of the mosquito larva host. The stylet is lost in subsequent larval stages and the stichosome separates from the intestine, which becomes a trophosome with no anal opening to the exterior.
Nutrient uptake from the insect hemolymph is through a very thin cuticle, perhaps enhanced by narrow diameter pores. The epidermal cells adjacent to the cuticle have their absorptive surface area increased buy outwardly-directed microvilli (Poinar and Hess, 1977; Munn and Munn, 2002).
The continued role of the stichosome is unclear although it appears to be involved in protein synthesis (Poinar, 1983).
The larva undergoes one molt in the insect host and then ruptures the body
wall as it emerges. After a final molt to the adult stage, the female deposits
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.
Ferris, H. 2007. Stichosomida. McGraw-Hill Encyclopedia of Science & Technology. http://accesscience.com/abstract.aspx?id=757377&referURL=http%3a%2f%2faccesscience.com%2fcontent.aspx%3fid%3d757377.
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.
Munn, E.A and Munn, P.D. 2002. Feeding and digestion. Pp 211-232 in Lee, D.L. (ed.). The Biology of Nematodes. Taylor and Francis, London and NY. 635p.
Poinar, G.O. and Hess, R. 1977. Romanomermis culicivorax: morphological evidence of transcuticular uptake. Experimental Parasitology 42:27-33.
Poinar, G.O. 1983. The Natural History of Nematodes. Prentice-Hall, Englewood
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