In schizocoelomates the coelom forms through

• A. Separation of mesoderm cells
• B. Out-pocketing of the embryonic gut into mesoderm space
• C. Formation from ectoderm
• D. Formation from endoderm

Answer: (A)

Schizocoelomates form the coelom by splitting the mesodermal mass. After mesoderm starts to form, blocks of mesoderm separate and spread apart, creating a fluid-filled cavity that becomes the coelom. This splitting process, or schizocoely, is what the term describes. It differs from enterocoely, where the coelomic cavities arise as pockets that bud off from the gut. The coelom is a mesoderm-derived space, not formed from ectoderm or endoderm, so options invoking formation from those germ layers aren’t correct. Thus, the coelom forms through the separation/splitting of mesodermal tissue.