Schizocoelous

Schizocoelous development is exclusive to protostomes: phyla Mollusca, Annelida, and Arthropoda. The term refers to the order of organization of cells in the gastrula leading to development of the coelom. In these three phyla of organisms, the mesoderm (the middle germ layer) forms as a solid mass of migrated cells from the single layer of the gastrula. The new mesoderm then splits, creating the pocket-like cavity of the coelom.