The giant barrel sponge (Xestospongia muta) is the largest species of sponge found growing on Caribbean coral reefs. It is common at depths greater than 10 metres (33 ft) down to 120 metres (390 ft) and can reach a diameter of 1.8 metres (6 feet). It is typically brownish-red to brownish-gray in color, with a hard or stony texture. The giant barrel sponge has been called the "redwood of the reef" because of its size and estimated lifespan of hundreds to a thousand or more years. It is perhaps the best-studied species of sponge in the sea; a population on Conch Reef, in the Florida Keys, has been monitored and studied since 1997.