Protostomes represent animals whose embryonic cells cleave in a spiral an the mouth opening develops before the anus. These animals do not always have a body cavity. Sponges, mollusks and arthropods are protostomes. Echnioderms, vertebrates and chordates are not protostomes, they are deuterostomes. Deuterostomes develop the anus before the mouth, cleave radial and have a true body cavity.
