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

Doug Perrine / Diver looking at Purple tube sponge {Aplysina lacunosa} Bahamas, Caribbean

Doug Perrine / Bottlenose dolphin {Tursiops truncatus} Cayman Islands, Caribbean Sea (Non-ex).

Doug Perrine / Bottlenose dolphin {Tursiops truncatus} Cayman Islands, Caribbean Sea (Non-ex).

Sergio Hanquet / Yellow umbrella slug (Tylodina perversa), two feeding on Golden sponge (Aplysina aerophoba). Tenerife, Canary Islands.

Sergio Hanquet / Yellow umbrella slug (Tylodina perversa) on Golden sponge (Aplysina aerophoba). Tenerife, Canary Islands.

Sergio Hanquet / Yellow umbrella slug (Tylodina perversa) feeding on Golden sponge (Aplysina aerophoba). Tenerife, Canary Islands.

Sergio Hanquet / Yellow umbrella slug (Tylodina perversa) on Golden sponge (Aplysina aerophoba). Tenerife, Canary Islands.

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

David Fleetham / Blue spiral fan (used for feeding and breathing) of Christmas tree worm (Spirobranchus giganteus) visible on reef. Maui, Hawaii.

David Fleetham / Caribbean trumpetfish (Aulostomus maculatus) camouflaged among Tube sponges (Aplysina sp). Bonaire, Netherlands Antilles, Caribbean.

Alex Mustard / Colourful coral reef wall, with yellow branching tube sponges (Pseudoceratina crassa), brown tube sponges (Agelas conifera) and red rope sponges (Amphimedon compressa), in front of deepwater sea fans...