Animal, Pseudocoelomates, or aschelminths

The pseudocoelomates include the nematodes, rotifers, gastrotrichs, and introverts. Some members of some other phyla are also, strictly speaking, pseudocoelomate. These four phyla of tiny body size (many species no larger than the bigger protozoans) are placed together in part because they lack mesoderm on the inner side of the body cavity. Consequently, no tissue,