Animals in which no body cavity develops are termed acoelomate . An animal body plan characterized by no body cavity present between the digestive tract and the outer body wall. The area between the digestive tract and outer wall is filled with cells, producing a solid body. Mesenteries connect the inner and outer mesoderm layers and suspend the internal organs in the coelom. The fluid cushions the organs thus preventing injury.
Internal organs can grow and move independently of the outer body wall.
Serves as a hydrostatic skeleton in soft bodied coelomates such as earthworms. In addition to the presence of a body cavity, acoelomates differ from pseudocoelomates and eucoelomates by not having a blood vascular system. Most protostomes undergo spiral cleavage and determinate cleavage during their development. Cleavage in which the planes of cell division are diagonal to the vertical axis of the embryo. Cleavage in which the developmental fate of each embryonic cell is established very early.