The ancestors of deuterstomes are the extinct yunnanozoans. They had a large mouth, 6 pairs of external gills, and a lightly cuticularized segmented posterior body section. Later in detuerostome evolution, gills became internal and connected to the exterior via slits in the body wall. These gill slists were lost in the echinoderms. Deuterostomate animals include:
The two major clades of deuterostomes are as follows:
Echinoderms & Hemichordates, which have a 3-part coelom and bilaterally symmetrical ciliated larva.
The chordates had a nonfeeding, tadpole-like larva and unique dorsal supporting structure.