Trichocephalida

The Trichocephalida is an order of parasitic nematodes.

Taxonomy

The order Trichocephalida includes, according to modern classifications, the single suborder Trichinellina Hodda, 2007, which itself includes the single superfamily Trichinelloidea Ward, 1907, which itself includes 6 families:

Family Anatrichosomatidae Yamaguti, 1961 including the single genus Anatrichosoma
Family Capillariidae Railliet, 1915 including Capillaria
Family Cystoopsidae Skrjabin, 1923
Family Trichinellidae Ward, 1907 including Trichinella
Family Trichosomoididae Hall, 1916 including Huffmanela
Family Trichuridae Ransom, 1911 including Trichuris

Note that another slightly different arrangement of families exists, with the Family Trichosomoididae including Anatrichosoma in a subfamily Anatrichosomatinae.

Biology

All members of this order are histiotrophic, meaning that in at least one stage of their life cycle, they develop in cells or tissues. They are all parasites in vertebrates in their adult stage. The anterior end is narrower than the posterior end in most of these worms, and the esophagus is slender and embedded in cells called stichocytes which form a stichosome. Eggs of members of this order have bipolar or biopercular plugs.