Phylum Nematomorpha - the horsehair worms. Larvae live inside insects and crabs. Gut is reduced or non functional. Phylum Loricifera - sand and mud worms. Phylum Platyhelminthes - the flatworms.
Digestive tract consists of a mouth and a dead-end sac that is branched for absorption.
Class Tubellaria - the planarians. Class Cestoda - the tape worms. Class Trematoda - the flukes. Internal parasites of vertebrates and cause disease. Class Monogenea - the monogeneans.