Alex Mustard / Yellow tube sponge (Aplysina fistularis) on coral reef, diver exploring in background. Black Rock Drop Off, East End, Grand Cayman, Cayman Islands, British West Indies. Model released.

Alex Mustard / Yellow tube sponge (Aplysina fistularis) on a coral reef, with the camera rotated during the long exposure. East End, Grand Cayman, Cayman Islands. British West Indies. Caribbean Sea.

Alex Mustard / Spotlight goby (Gobiosoma louisae) looking out from inside a Yellow tube sponge (Aplysina fistularis), growing on a coral reef. Bloody Bay Wall, Little Cayman, Cayman Islands, British West Indies. Car...

Alex Mustard / Yellow tube sponges (Aplysina fistularis) growing on a Caribbean coral reef. Cayman Brac, Cayman Islands. Caribbean Sea.

Alex Mustard / Yellow tube sponge (Aplysina fistularis) top view of tubes with water swirling around them, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Jeff Rotman / Yellow tube sponge (Aplysina fistularis) Red Sea, Egypt

Doug Perrine / Yellow tube sponge {Aplysina fistularis} with Yellowtail snappers {Ocyurus chrysurus Cayman Brac, Cayman Islands, Caribbean

Franco Banfi / Yellow tube sponge (Aplysina fistularis) Dominica, Caribbean Sea, Atlantic Ocean

Franco Banfi / Spotted moray eel (Gymnothorax moringa) inside Yellow tube sponges (Aplysina fistularis) Dominica, Caribbean Sea, Atlantic Ocean.

Pete Oxford / Yellow tube sponge (Aplysina fistularis) Lighthouse Reef Atoll, Belize Barrier Reef, the second largest barrier reef system in the world. Belize.

Claudio Contreras / Yellow tube sponge (Aplysina fistularis) Cozumel Reefs National Park, Cozumel Island, Caribbean Sea, Mexico, January

Claudio Contreras / Yellow tube sponge (Aplysina fistularis) Cozumel Reefs National Park, Cozumel Island, Caribbean Sea, Mexico, February