Animal groups, like flatworms, with no such space are referred to as acoelomates . Animals, such as roundworms, which have a space between the mesoderm and the endoderm are called pseudocoelomates , and the space is called a pseudocoelom . Animals, including earthworms, insects, and humans, which have the space in between several of the mesoderm layers are called coelomates , and the space is called a coelom . These are the sponges. Sponges are hermaphroditic , that is, they have both sexes in one body.
Sponges have no symmetry.
These animals have radial symmetry. The one opening serves as both a mouth to ingest food and for expulsion of any wastes. The bodies of cnidarians are described in one of two ways, depending on whether the opening of the gastrovascular cavity is ventral or dorsal. Cnidarian tentacles serve to capture prey. These tentacles bear stinging cells, called cnidocytes , to subdue their prey, and some jellyfish cnidocytes irritating or toxic to humans.