Worms from the phylum Nematoda or the phylum  Annelida have some sort of body cavity— a fluid-filled space between the body  wall and the digestive tract that helps transport nutrients and corresponds to  the development of more complex systems.

来自线虫或环节的蠕虫具有一种体腔——于身体壁和消化道之充满液体的，有助于运输营养质，并对应着更复杂系统的发展。