The creatures of the dark depths of the ocean are some of the strangest and most mysterious in the world. One common adaptation for these creatures is the ability to glow in the dark, known as bioluminescence. This glow is created by special types of chemical reactions in bacteria, and the results are spectacular. There is a great video by National Geographic on the subject, containing some fantastic footage of these rarely seen deep sea denizens.
I wish to someday dive that deep in the ocean! =)