The vampire squid (Vampyroteuthis infernalis, literally: vampire squid from Hell) is actually more beautiful than hellish, I think. This squid does not live at the same depths as the number one entry on this list, but at 600-900 metres, it still dwells a long way down as far as squid are concerned. At the upper levels of its range, there is some sunlight, and as a consequence it has evolved the biggest eyes of any animal (in proportion to size) in order to capture as much light as it can. What is really fascinating about this animal are its defense mechanisms. In the dark seas that it lives in, it releases bioluminescent ‘ink’ that dazzles and confuses other animals while it escapes.

 And check out this cool video, where a vampire squid turns itself ‘inside out’ to avoid predators: www.youtube.com/watch?v=IWAnliNc6wk. This works a bit better when the sea around it is not illuminated. Normally, it can emit a bluish light which, seen from underneath, helps to camouflage; but when spotted, it wraps itself with its black-coloured underside… and disappears.