Franco Banfi / Squat lobster (Lauriea siagiani) on Sponge (Xestospongia), Cabilao House Reef, Cabilao Island, Bohol, Central Visayas, Philippines, Pacific Ocean.

Alex Mustard / Black grouper (Mycteroperca bonaci) yawns as it visits a cleaning station on a coral reef, beside a giant barrel sponge (Xestospongia muta). Jardines de la Reina, Gardens of the Queen National Park, C...

Franco Banfi / Barrel sponge (Xestospongia testudinaria) Tubbataha Reef Natural Park, UNESCO World Heritage Site, Sulu Sea, Cagayancillo, Palawan, Philippines

Georgette Douwma / Black coral (Antipathes dichotoma) and Barrel sponge (Xestospongia testudinaria) in coral reef, West Papua, Indonesia.

Linda Pitkin / Barrel sponge (Xestospongia testudinaria), beneath roots of mangroves (Rhizophora sp.). Diver photographing Mangrove Ridge, Yanggefo Island, Raja Ampat, West Papua, Indonesia, March 2016

Claudio Contreras / Giant barrel sponge (Xestospongia muta) Cozumel Reefs National Park, Cozumel Island, Caribbean Sea, Mexico, January

Alex Mustard / Diver swimming through Tolberone Tunnel, a triangular tunnel through the middle of an island in Raja Ampat. Giant barrel sponges (Xestospongia muta) growing on the floor of the tunnel, which have an u...

Juergen Freund / Giant barrel sponge (Xestospongia testudinaria) with crinoids, Kimbe Bay, West New Britain, Papua New Guinea.

Pascal Kobeh / Diver near barrel sponge (Xestospongia testudinaria), hard coral (Porites sp) and red whip coral (Ctenocella sp), Walindi, Papua New Guinea, Bismarck Sea.

Pascal Kobeh / Caribbean spiny lobster (Panulirus argus) in a giant barrel sponge (Xestospongia muta), San Salvador Island / Colombus Island, Bahamas. Caribbean.

Pascal Kobeh / Caribbean spiny lobster (Panulirus argus) in Giant barrel sponge (Xestospongia muta), San Salvador Island / Colombus Island, Bahamas. Caribbean.

Pascal Kobeh / Hawksbill turtle (Eretmochelys imbricata) feeding on a Leathery barrel sponge (Geodia neptuni), San Salvador Island / Colombus Island, Bahamas. Caribbean.