Echinoids - The class Echinoidea includes the sea urchins, heart urchins, cake urchins and familiar sand dollars. The sea urchins are well known to most people, having a large number of sharp spines pointing out in all directions.

Holothuroids - The class Holothuroidea is composed of creatures called sea cucumbers. A sea cucumber is so named due to the fact that many members of the group (but not all) resemble the garden variety of cucumber. The similarity ends there.