Eunice Aphroditois, The Bobbit Worm

Armed with sharp teeth, it is known to attack with such speeds that its prey is sometimes sliced in half. Although the worm hunts for food, it is omnivorous. It is also covered in bristles that are capable of a sting that results in permanent numbness in humans.
Little is known about the sexual habits and life span of this worm, but researchers hypothesize that sexual reproduction occurs at an early stage, maybe even when the worm is about 100 millimetres (3.9 in) in length; this is very early, considering that these worms can grow to sizes of nearly 3 metres (9.8 ft) in some cases (although most observations point to a much lower average length of 1 metre (3 ft 3 in)) and an average of 25 millimetres (0.98 in) in diameter. A long lifespan may very well explain the size of these creatures.
Eunice aphroditois is found in warmer oceans around the world, including the Indo-Pacific and Atlantic.
In March 2009, the Blue Reef Aquarium in Newquay, Cornwall, discovered a bobbit worm in one of their tanks. The workers had seen the devastation caused by the worm, such as fish being injured or disappearing and coral being sliced in half, but didn't find it until they started taking the display apart in the tank.