A reef creature is an organism that lives in coral reefs, which are underwater ecosystems found in tropical and subtropical waters. Two examples of reef creatures are sponges and seahorses. Sponges are filter feeders that live attached to the substrate of the reef and can come in a variety of shapes and sizes. Seahorses are small fish with a prehensile tail and a head that resembles a horse, and they use their tail to anchor themselves to coral or seaweed.