Thresher shark (Nicolas Voisin / shutterstock.com)
The thresher shark (Alopias sp.) is easily identified by its large eyes and its whiplike caudal fin that can be as long as its entire body. Thresher sharks range from 3 meters (9.8 inches) to 6.1 meters (20 feet, common thresher, Alopias vulpinus) in length and feed on schooling pelagic fish, squid, and cuttlefish. Thresher sharks use their tails as weapons to stun or kill prey. They are considered harmless to divers.