I find cephalopods like octopuses, squid and cuttlefish fascinating. They are really intelligent and like true aliens on our own planet.

They have eyes that are organised in a much more efficient way than ours - instead of the backwards way where our blood vessels and some neural fibres are in front of the photoreceptors (reducing effective resolution) they have things arranged in the more logical manner. That is they have the photoreceptors at the front.

They also have some other fascinating eye differences that are well worth reading about but I won't write a long essay here. It is considered a good example of convergent evolution since it is almost impossible that the vertebrate eyes that we have are derived from the same evolutionary source.