Answer:
Most zoologists believe that echinoderms share a common ancestry with hemichordates and chordates because of:
1. The deuterostome characteristics that they share (see figure 1),
2. An anus that develops in the region of the blastopore.
3. A coelom that forms from outpockets of the embryonic gut tract (vertebrate chordates are an exception).
4. And radial, indeterminate cleavage.
