Body
Sea star as juveniles have bilateral symmetry, but when the mature they have radial symmetry. Unlike sea stars, sea urchins and sand dollars always posses radial symmetry. Inside they have a complex water vascular system. The water vascular system consist of canal through the tube feet. It aids in sensory, and respiratory tasks. It also helps out during meal time. In order for a starfish to eat a clam or any bivalve creature it must open the two shells, and to do this it uses the water vascular system to pump water into the clam, so it can pry it open easier. Altogether each detail of an echinoderms body is useful and necessary.
Reproduction
Echinoderms can reproduce both asexually and sexually. They reproduce asexually by fragmentation, which means if they break apart or lose part of their body it will regrow, plus the same will happen to the parent of the fragment; it will grow back the lost part of the body. Echinoderms can reproduce sexually by both the female and male shed their eggs/sperm into the water. Next, the egg and sperm meet together and start to grow. After all those stages occur a beautiful young creature has joined the ocean.