They are now by many systematists united with the Acanthocephala and the Nematomorpha to form the group Nemathelminthes.
ACANTHOCEPHALA, a compact group of cylindrical, parasitic worms, with no near allies in the animal kingdom.
Food is imbibed through the skin from the digestive juices of the host in which the Acanthocephala live.
The Acanthocephala are dioecious.
Certain additional small groups should probably be recognized as independent lines of descent or phyla, but their relationships are obscure - they are the Mesozoa, the Polyzoa, the Acanthocephala and the Gastrotricha.