Scaly on top, bumpy on the bottom. When humans hold them they usually close their mouth which sits underneath them.
Some starfish have spines, humans should not touch those.
"The mouth is located underneath the sea star, on its ventral surface. The spiny upper surface is called the aboral or dorsal surface."
"A sea star may have dense rows of spines as a means of protection, or it may have no spines at all."
|Includes CC-BY-SA content from Wikipedia's Sea_star article (authors)|