Although they look similar to the sea stars, there are some major morphological differences between these two groups. 

As the hobby of keeping marine animals has evolved, greater emphasis has been placed on keeping a wider diversity of animals. 

All echinoderms share several common characteristics despite very dissimilar outward appearances differentiating them from all other members of the animal kingdom. 

Echinoderms possess an interesting defensive structure called the pedicellaria. These external jaw-like structures are located not only on the ends of arms but are also found along the body.