Eunice aphroditois (Bobbit Worm)

Eunice aphroditois

This is Eunice aphroditois, also known as the Bobbit Worm. This alien looking creature lives in the tropical ocean's near coral reefs. They seem to come in a variety of different colors and sizes. It has been known to grow to lengths of 10 feet or more.
The Bobbit Worm submerges itself in sand or soil on the ocean floor leaving only a few inches of its head exposed, ready to ambush any fish that may be unfortunate enough to come close enough for it to grab. As if that isn't disturbing enough, it then proceeds to grasp on to it's prey with the pharynx (mouth piece) at the front of it's head and pull it into the ground much like the graboids from Tremors. Talk about freaky, this thing is just plain out bizarre.

Even stranger than that, these subterranean serpents seem to have a knack for finding their way into salt water aquariums, more than likely brought in with rocks or sand as a juvenile and basically fed their own private stock of fish until adulthood. 
Here is a video of one feeding for anyone brave enough to watch. It's pretty astonishing.