Cephalopods (octopuses, squids, nautilus, etc.) are among the most complex invertebrates. They have been around since before the dinosaurs. Yet, there are none that tolerate fresh water today - perhaps there never have been (I am aware there is one squid in Chesapeake that lives in brackish water). This leads me to wonder about a few things: What is it about this class of molluscs that prevents them from exploiting fresh water environments? Is this why they also have not given rise to any land forms? Is tolerance of fresh water essential to evolution to living on the land? Were the predecessors (e.g. tiktaalik) of the first land vertebrates, fresh water animals?