Echinoderms. Developed By Adam F Sprague & Dave Werner MATES Biology (Marine Bio Book – Ch.7) (Biology Book – Ch.40 also pp.682-686). 5 classes of Echinoderms. Sea star or starfish (Asteroidea) Brittle stars, basket stars, serpent stars ( Ophiuroidea )
Developed By Adam F Sprague & Dave Werner
(Marine Bio Book – Ch.7)
(Biology Book – Ch.40 also pp.682-686)
Anatomy of an adult sea star. Lower (right) image is a cross section through an arm of the adult sea star. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
The answer lies in the development of the embryo. If you were to watch an embryonic starfish develop, you would see that it begins life bilaterally, but switches to radial symmetry as it matures.