FIGURE 29.5
A comparison of early development in protostomes and deuterostomes. (a) Protostomes have spiral, determinate cleavage; deuterostomes have radial, indeterminate cleavage. (b) The blastopore of the gastrula forms the mouth in protostomes; the mouth forms from a secondary opening in deuterostome. (c) Coelom formation also begins in the gastrula stage. In the schizocoelous development of protostomes, the coelom from splits in the mesoderm. In the enterocoelous development of deuterostomes, the coelom forms from mesodermal outpocketings of the archenteron (blue = ectoderm, yellow = endoderm, red =mesoderm).