Chambered Nautilus, Nautilus belauensis. These cephalopods (members of the squid family) are some of the most ancient critters still around, having been around in the age of the trilobites. Compared to the cuttlefish, a relative, that I posted the other day, you can see that the eye structure looks much simpler and cruder. You may have seen these shells for sale in the store, sliced down the midline (medially). In the center of the spiral is a tiny hole that extends through each chamber. These chambers are filled with air and used to control bouyancy. In their native environment they migrate daily from very deep water during the day to shallow depths during the night to feed, the buoyancy control enabling them to traverse these great depths. I'm not sure if part of the nautilus (the critter) extends all the way back through the different chambers or if the hole is there to pass air in and out of the rear chambers. In either case, it's pretty amazing stuff!
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