[3] The giant barrel sponge has been called the "redwood of the reef"[4] because of its large size and its long lifespan, which can be more than 2,000 years.

[5] 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.

[3] In shallow water, the color is brownish-red to brownish-gray; but, at greater depths and in caves and under-hangs, or when the sponge is undergoing cyclic bleaching events, it is pinkish or white.

[8] On the reefs off the Florida Keys, it may be as common at two individuals per square metre (yard), and the total biomass of the sponge is greater than any other benthic invertebrate.

[6] Two or more closely related species that are visually indistinguishable from X. muta are found on reefs in the Pacific and Indian Oceans (particularly Xestospongia testudinaria).

Clouds of sperm from males are emitted from the osculum, while females produce flocculent masses of eggs that are slightly negatively buoyant.

[11] Resulting sponge larvae disperse with ocean currents, but there is some genetic differentiation among populations from Florida, the Bahamas and Belize.

Sponges filter large amounts of water, and are a predominant link in benthic-pelagic coupling on reefs and they harbor diverse assemblages of bacteria that can take part in nitrification and carbon fixation.