1. Phylum Echinodermata marine only radial symmetry; oral/aboral surfaces calcareous endoskeleton made of ossicles lack excretory & circulatory system non-metameric regenerative

2. Natural History benthic; predators & scavengers two part stomach cardiac stomach may be everted pyloric stomach contains the gastric caecae; increased surface area reproduction: mostly dioecious external fertilization swimming larvae (bilaterally symmetrical, ciliated)

3. Class Crinoidea sea lilies & feather stars most primitive extant group tropics mainly long, feathery arms around the mouth; suspension feeders

4. Class Echinoidea sea urchins, sand dollars, & sea biscuits spherical test without arms pentamerous plates with long movable spines algae or deposits

5. Class Holothuroidea sea cucumbers reduced endoskeleton; leathery body secondarily bilateral tube feet modified as tentacles evisceration-

6. Class Stelleroidea brittle stars & starfish most diverse group autotomy- arms detach readily distinct central disk