Anglerfish have some really weird body parts.
1) A built-in 'lure' to attract prey. It's a long filament extending from the fish's head, and sometimes it even glows in the dark. Little fish will swim near to see what it is, and the anglerfish will chow down. For a pop-culture reference, there's a great anglerfish scene in "Finding Nemo".
2) Males. Seriously, they are just a body part. The male anglerfish is a tiny little critter (compared to the female) and can't even survive on his own for very long. When he finds a female he attaches himself to her by biting her belly and releasing enzymes that fuse their flesh together. Eventually his whole body wastes away until he's nothing but testicles, attached to her and fertilizing her eggs.
