Anglerfish

Some anglerfish, who live in the ocean at depths of over one mile, have unusual lives. To see where they are going in that depth, or perhaps to attract food, the females have a chemically operated lamp that hangs on a stalk in front of their mouths. The male doesn’t need to see because early in his life, he bites into the belly of the female and stays there forever. After a while the female grows skin over the connection. The male degenerates, losing his teeth, his fins, and any manner of life beyond being a small appendage hanging off the female.