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Starfish (scientifically known as Asteroids and Ophiuroids) first appear in the fossil record in the Lower Ordovician. They are members of the phylum Echinodermata, the largest phylum of strictly marine creatures. Starfish are included in this group along with animals such as sea urchins, sea cucumbers and sand dollars. Most living echinoderms have a five-fold symmetry called Pentameral. This is not always the case though, and despite the common five arms, there are starfish species that have many more then just five. Echinoderms have an internal water canal system and tube feet with suckers that they use to move, burrow and grasp objects. Because of their overall fragile nature, starfish are rarely preserved as complete specimens.

Brittle stars are a type of starfish that are uniquely classified in their own group called Ophiuroidea. The ophiuroids possess five long and fragile arms radiating out from a small, round disc-shaped body. Brittle stars lack the bulk and thickness of the asteroids and are lightly armored.