This has puzzled me for years. They are very highly developed lifeforms, but they're only found in saltwater. There aren't even any freshwater cephalopods. But it isn't hard to imagine cephalopods frolicking on dry land like the tree squid. If snails have made it by developing lungs, slime and a foot suited to overland locomotion, why can't their relatives? They had millions and millions of years to do it.

Maybe we'll see land snails developing tentacles and lens eyes over the next eon.

Anark: The 'neural wiring' of cephalopod eyes is, if not better, certainly more logical than that of mammalian eyes. The reason is that, evolutionarily, the cephalopod eye developed from the outside in: a photosensitive spot became a dimple, then a camera obscura eye and finally a lens eye. I know much less about the mammalian eye, but it developed from the inside out -- it descends from brain tissue, not skin tissue, in layman's terms (I use these because I am a layman). Thus, the optical nerve in a human eye needs to connect to the outer side of the retina, whereas in a cephalopod eye, it connects to the backside like any sane electrical engineer would do it (does your TV's antenna cable come out of the screen?). That means that cephalopods haven't got a blind spot, but mammals do.

This is an interesting question, and since I just got out of a biology lab final, I thought I'd add my ideas...

For one thing, they're too mushy... just about everything on land has a skeleton of some sort. Insects have exoskeletons, while vertebrates have endoskeletons. Most molluscs have shells which are kind of like exoskeletons... but octopi have lost these. The nautilus still have them but I can't imagine them as a land animal. Slugs manage to exist without an exoskeleton, and are molluscs. However, they have to remain small and don't have much room for tentacles/a brain/ etc.

For another thing, cephalopods just work really well in water. They are products of a very long line of evolution, perfecting them for a marine life. They can move very fast, have very dexterous tentacles, advanced eyes, large brains, ink, etc... if they left for land, none of these things would be able to exist in the current form. So, they'd end up back to the level of slugs, probably.

There's already a lot of competition on land... mammals, insects, reptiles, etc, have pretty much taken up every ecological niche possible. For a cephalopod to thrive on land it would have to be able to compete with these. They'd be much slower on land, barely able to survive under their own weight... which doesn't make for a good predator. And it isn't likely they'd be able to become herbivores. (the same basic idea has been applied to why insects aren't found in marine areas.. there simply isn't anywhere for them to go, ecosystem-wise). Anyway, if a mass extinction killed most chordates on land, perhaps the cephalopods would have a chance. But until then...

It's said that scientists who work with squids and octopuses fall in love with them: not in an anime sense, but ascribing all sorts of dolphin-like beauties to them. I can understand this. I too have been fascinated by the idea of land cephalopods. Giant land cephalopods, of course. Intelligent giant land cephalopods, of course.

Squids have got wonderful things like jet propulsion, invisibility, giant tentacles, and huge razor-sharp beaks. I believe that some of them can launch themselves above the water surface and fly, using a jet burst. This is scary enough. Now combine them with all the best genes from octopuses.

The blue-ringed octopus has one of the deadliest poisons of any creature. An octopus in a laboratory tank can squeeze itself into a tiny space and escape, oozing through unbelievably small cavities. And they are reported as using tools. This hasn't been confirmed by repeated observation, it's true, but they have been seen picking up a stone and putting it inside a clam shell to prevent it shutting, so that they can make a meal at leisure. Octopuses pass intelligence tests as easily as rats and pigeons.

How did our own fishy ancestors make the transition to land? Lungfish that could survive with a bladder full of air when the pools dried up, and that could waddle through the mud from one pool to another -- a bit of a Just So Story, but it'll do for our purpose. Now a squid is probably too streamlined and oceanic to get anywhere near the littoral, but I can easily imagine octopuses lying in wait in shallow rock pools. Heavens, the blue-ringed octopus does.

Give it a more leathery skin, so it doesn't dry up on exposure. It crawls around the seabed on its cute little legs already, so that's not a problem. Let it start by slithering over the seaweedy rock-flats pulling up limpets: that's not such a jump in fitness space.

To make it permanently ambulant on land we'd have to overcome the skeletal support problem. Well we could postulate some new development -- but let's say a simple reversal of the homeobox genes could give it the endoskeleton of a cuttlefish. But broken up. Articulated, joined by cartilage. Or exapt the radula: make it longer and longer, curl it round, break it into pieces, until it can act as an endoskeleton.

Then you've got giant invisible flying poisonous super-intelligent multi-tentacled carnivores. R'lyeh! R'lyeh!

Two little things to add since originally writing this. Cephalopods aren't as continuously active as mammals because their blood contains the copper-based haemocyanin instead of our iron-based haemoglobin, and this stores oxygen more efficiently than it can release it. Secondly: the name says it all, Vampyroteuthis infernalis, the Vampire Squid from Hell.

All of your dreams will come true. Two hundred million years from now, the squid will emerge triumphantly as the largest land animal. The megasquid will weigh 8 tons. Large muscular legs will support his royal bulk, and it will have no skeleton to speak of. By that time, the continents have once again merged to form a supercontinent called Pangea II. In the northwest corner of this uber-continent will be a dense forest with drenching rainstorms, an atmosphere high in carbon dioxide, and conifers the size of today's Redwoods. This will be the domain of the megasquid. The mighty cephalopod will have a special network of muscles in its legs that are both vertical and circular. To walk the megasquid will alternately swing his enormous legs forward. When the megasquid stands still, its legs will lock and the cartilage-like muscles will serve as a base. Also, the giant land squid will have 6-foot tentacles to grasp fruit and leaves. To breathe and emit calls, it will use a vocal sac on its forehead. The MEGASQUID's ancestors are the elusive giant squid, the cuttlefish, and the octopus.

That's what the experts at Animal Planet say. You can believe whatever you want. Just warn your children to warn their children, to warn their children, let sleeping megasquids lie.

To find more about all the amazing animals, go to The most interesting facts and things are at the "Animals at Warp Speed" link.

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