You know those nasty tunneling sandworms nicknamed “graboids” from the Tremors movies? As the franchise rolled along, the filmmakers tried assorted mutant variations on the original theme, including bipedal "shriekers" and airborne versions with the awesome nickname "ass blasters." But they never took the idea underneath the water... and that's okay, because nature's already done that.
Enter Eunice aphroditois, alias the bobbit worm. Some claim it's named after notorious husband-castrator Loreena Bobbitt, and while that would be pretty amazing, it's not entirely proven (although the worm does have serious chopping skills, as you'll see below). The tropical monstrosity, which can grow to ten feet long, really is an aquatic version of the graboid – a carnivorous nocturnal predator that burrows deep beneath the seabed, with only its rainbow-hued head above the sand, waiting for an unsuspecting fish to wander by. When the prey is close enough, the worm's jaws – which have scissor-like blades called pharynx – are often powerful enough to snap it in half. Watch it in action:
In an article for Wired, ecologists Luis F. Carrera-Parra and Sergio I. Salazar-Vallejo, who specialize in studying species like these, said they're still not entirely sure how the bobbit worm handles still-living prey, but theorize that its jaws inject a toxin potent enough to incapacitate fish for easier snacking. That toxin, which may also be produced by other parts of its body, has the potential to paralyze a human who gets too close. But we haven't even told you the best part yet.
You see, the bobbit worm has a tendency to just show up uninvited in aquariums – they get in by stowing away on rocks and coral that are introduced into the tanks, and then one day start murdering the hell out of all the fish in nightly killing sprees. One of the nastier cases happened four years ago at Newquay's Blue Reef Aquarium in the UK, when the aquarium's owners had to dismantle their tank completely to remove the killer worm... whom they had nicknamed “Barry.” How adorable.