Not unlike Garth Brooks concerts and Applebee's, the deep sea is one of those places you don't need to visit to know that it sucks. Down in the depths, mates are hard to find, thus the male anglerfish bites onto a female and fuses to her body, living the rest of his bummer of a life as a gonad. In the blackness seeing is next to impossible, even with the huge eyes of, say, the giant squid. And you really never know when you'll get your next meal, so you'd do well to have an outsized mouth to take on whatever comes your way.

It also doesn't hurt to have row after row of backward-facing, needle-like teeth—hundreds and hundreds of them, each forked into three nasty prongs. Such is the grotesque mouth of the frilled shark, surely one of the more bizarre sharks in the sea. And it's a mouth that biologist David A. Ebert, director of the Pacific Shark Research Center, knows all too well to respect.

"I can tell you from snagging my fingers on the teeth, you can only back out one way and that's in toward the mouth and then out," he said. "It didn't feel good, I can tell you that."