Ascaridida

The order Ascaridida includes several families of parasitic roundworms with three "lips" on the anterior end. They are sometimes placed in the subclass Rhabditia, but more often in the Spiruria.

Important families include:
 * Ascarididae, which includes the giant intestinal roundworm and related species.
 * Toxocaridae, which includes parasites of canids, felids, and raccoons, but which can unsuccessfully parasitize humans and cause visceral larva migrans.
 * Anisakidae, also called the marine mammal Ascarids. The larvae of these worms cause anisakiasis when ingested by humans, but do not reproduce.