There are over 800 different species of sea urchins varying greatly in appearance, ranging in size from less than an inch to over a foot across in an assortment of shapes and colors. 

While sea urchins may be considered the brutes of the echinoderms, feather stars are the delicate flowers of the group. 

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.