Sand Dollars are actually related to the Sea Urchins. Both belong to the Phylum Echinodermata. Sand Dollars and Sea Biscuits belong to the order Clypeastroida while Sea Urchins belong to the order Echinoida. Other orders in Echinodermata are Cidaroida (pencil urchins), Spatangoida (heart urchins) and Cassiduloida (a rare sand dollar-like group). Sea Biscuits look like cookies while Sand Dollars are very flat.

They can be found huddled together in sandy depressions where they feed.