Trichocephalida

The Trichocephalida (Trichinellida or Trichurida in other classifications) is an order of parasitic nematodes.
Taxonomy.
The order Trichocephalida includes, according to modern classifications, the single suborder Trichinellina , which itself includes the single superfamily Trichinelloidea , which itself includes 6 families:
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 (except in a few species).