phyla

They belong to the two phyla Platyhelminthes (flat-worms) and Nemathelminthes (thread-worms, &c.).

The animal kingdom has a varying number of divisions, called branches, subkingdoms, or phyla.

According to it the seven phyla, or tribes, of the animal kingdom are of different value in regard to genealogy.

The group is an isolated one and shows no clear affinities with any of the great phyla.

The conclusion that the Crustacea and Tracheata belong to two distinct phyla is confirmed by a consideration of their development.