Eunice aphroditois

Eunice aphroditois, also known as the bobbit worm (or bobbitt worm) or sand striker, is an ambush predator of the sea floor. It is a polychaete worm dwelling in a burrow on the ocean floor. It buries its long body into the ocean bed of gravel, mud, or corals. It waves a few feelers (antennae) as a kind of lure.
When it feels a stimulus to one of its feelers, it attacks if it senses prey. Armed with sharp pincers, it attacks with such speed and ferocity that its prey is sometimes sliced in half. Usually, it drags the prey down into its burrow, and eats it there.
The procedure is well captured on YouTube, where the worm goes by the name of bobbit worm.