I've mentioned before my long time interest in giant squid. I am amazed that something so big can remain largely a scientific mystery.
Cuttlefish, which are smaller relatives, have an incredible capacity to change the appearance of their skin in order to communicate with their squidly counterparts. Ed, over at the blog Not Exactly Rocket Science (a good all around science blog, btw) has a great post on the subject and here's a quote about how it works:
The top layer consists of specialised sacs of coloured pigment called chromatophores, which can expand or contract on command. By switching them from concentrated specks to flat plates, the squid can produce rapid bursts of colour.
But the key to secret signalling lies in the bottom layer. This consist of cells called iridophores, which contain stacked plates of protein separated by liquid. When light hits each plate, some is reflected but the rest passes through to the other plates below. The squid can control the size of the gap between the plates, so that they match the wavelength of different colours of light.
Go read the rest of the post, it's very interesting.
Seeing it reminded me of when I worked a couple of summers as a seasonal naturalist for the state park system in Ohio. At the training, we'd go through this catalog of films (yes, like we saw in grade school) on various topics that we were supposed to show at the campfire program on Saturday night. I tried to pick things that were either just entertainment ("What's that Lassie? Timmy's down in the well?") or sciencey.
One was on cuttlefish, and it was one of those things that you think, 'well, that looks OK' and after you see it, you think 'I can't believe there are creatures like that!' As they say in the video below, from a PBS NOVA episode, it's pretty wild that something related to a slug has such a complex brain. Did you notice how big their eyes are when they're not trying to hide them? Wow.
The NOVA link is to their website that has a lot more info on this phenomenon.