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.

Georgette Douwma / Stove-pipe sponge (Aplysina archeri) and Orange elephant ear sponge (Agelas clathrodes) Bonaire, Netherlands Antilles, Caribbean, Atlantic Ocean.

Alex Mustard / A diver exploring a coral reef with formation of brown tube sponges (Agelas conifera) red rope sponges (Amphimedon compressa) and deepwater sea fans (Iciligorgia nodulifera) East End, Grand Cayman, Ca...

Juergen Freund / Orange cup coral (Tubastrea faulkneri) with polyps open, Batangas, Philippines.

Juergen Freund / Orange cup coral (Tubastrea faulkneri) detail of mouth and tentacles, Batangas, Philippines.

Norbert Wu / Orange Tube Coral (Tubastraea aurea) polyps extended only at night, Dutch Antilles, Caribbean

Georgette Douwma / Tube coral polyps feeding {Tubastrea faulkneri} Milne Bay, Papua New Guinea

Magnus Lundgren / Wild Wonders of China / Yellow tube coral (Tubastrea faulkneri) with the polyps open, Ninepin Group or Kwo Chau Islands, Hong Kong, China.

Magnus Lundgren / Wild Wonders of China / Sun / Tube coral (Tubastraea sp) with tentacles extended to catch zooplankton. Gulf of Bohai, Yellow Sea. Penglai / Dengzhou / Tengchow, Yantai, Shandong Province, China.

Magnus Lundgren / Wild Wonders of China / Sun / Tube coral (Tubastraea sp) with tentacles extended to catch zooplankton. Gulf of Bohai, Yellow Sea. Penglai / Dengzhou / Tengchow, Yantai, Shandong Province, China.

Linda Pitkin / Orange cup coral (Tubastraea sp.), and soft corals, Triton Bay, near Kaimana, West Papua, Indonesia

Linda Pitkin / Orange cup corals (Tubastraea sp.), Triton Bay, near Kaimana, West Papua, Indonesia