Asgeir Helgestad / Reindeer bull + calf {Rangifer tarandus} Buskerud, Norefjell, Norway

Fred Bavendam / Grey Nurse Shark (Carcharias taurus) swimming over reef, New South Wales, Australia

Fred Bavendam / Grey Nurse Shark (Carcharias taurus), New South Wales, Australia

Michael Pitts / Nurse shark {Ginglymostoma cirratum} seeking shelter under the stern of a sunken fishing boat. British Virgin Islands.

Francis Abbott / Tawny nurse shark {Nebrius ferrugineus} swimming over coral reef, Indian Ocean

Francis Abbott / Tawny nurse shark {Nebrius ferrugineus} swimming over coral reef, Indian Ocean

Jeff Rotman / Nurse Shark (Ginglymostoma cirratum) feeding on bait with schooling sharks and reef fish, Bahamas, Caribbean Sea.

Norbert Wu / Grey Nurse Shark (Carcharias taurus) swimming near Papoose Wreck off North Carolina

Norbert Wu / Grey Nurse Shark (Carcharias taurus) pair and other small fish swimming through Papoose Wreck off North Carolina

Norbert Wu / Grey Nurse Shark (Carcharias taurus) swimming through Papoose Wreck with other small fish, off North Carolina

Norbert Wu / Grey Nurse Shark (Carcharias taurus) swimming through Papoose Wreck off North Carolina

Juergen Freund / Nurse shark (Ginglymostoma cirratum) Caribbean

Doug Perrine / Teeth of Sand tiger shark {Carcharias taurus} or Grey nurse shark {Odontaspis taurus}