Strongyloides stercoralis has various life stages that include: and egg, rhabditform larvae, filariform larvae, and adult forms. The adult form that is found in the small intestines of its mammalian host ranges between 0.9 to 1.5mm in length and has a long, cylindrical body. Free-living males can be up to 0.9mm, and larvae can grow to 800µm. Like most nematodes, Strongyloides stercoralis is made up of four tissue layers: the epicuticle, exocuticle, mesocuticle, and endocuticle. The mouth of the nematode opens to the buccal capsule which is small relative to other nematodes. The buccal capsule is connected to the elongated esophagus which lacks a posterior bulb unlike other nematodes. The esophagus is connected to the intestine which is divided into three regions and connects to the rectum.
The body capsule, or pseudocoel, also contains the reproductive organs. For males, vas deferens extend throughout the body cavity from the testes and widen to form the seminal vesicles. Males also have copulatory spicules and a gubernaculum. Females, on the other hand, typically have two ovaries with an oviduct extending from it connecting the ovaries to the uterus via a seminal receptacle. There is also a difference between the free-living and parasitic forms of female nematodes; free-living female nematodes have uteri at the posterior end of the nematode containing more eggs than the parasitic females which have their uteri located more equatorial.
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