Addressing concerns about focus:

What advantage did an octopus with a more flexible tentacle have over an octopus with a less flexible tentacle? It seems it must have been something unusual.

It seems an octopus has the most dexterous limbs in the animal kingdom. Mesmerizing Video Study Reveals How Octopus Arms Are So Incredibly Flexible.

This seems to be the opposite of most aquatic animals. Fish have limbs adapted to swimming. They have no ability to grasp anything except with their mouths. Jellyfish have tentacles, but no ability to do anything with them. They passively wait for prey to brush against them. Barnacles have feet that they sweep up food with. Crabs have rather clumsy looking claws.

Hagfish have dexterous bodies. They can tie themselves in a knot and slide the know along their length. Combined with their slimy skin, this allows them to pull themselves out of your grasp. But I don't know that they make any particular use of this flexibility. Reaching into tight places for food?

On land, limbs are mostly legs or wings. Elephants have trunks. Snakes are flexible. Animals that climb trees are the only one that seem to have hands.

It seems that the ability to grasp and manipulate objects is an evolutionary afterthought. Animals that have the ability to hold onto trees have adapted to hold onto other things like food. Animals without hands bite their food in place. Animals with hands pick it up and carry it to their mouths.

So what made it advantageous for an octopus to take tentacles so much farther than anything else? Why do they need to pick up food? Was that the primary thing they evolved to do?

Octopi are mobile, but much less so than fish. They hide under rocks, while fish often swim in the open. Why is mobility less important than whatever else they use limbs for?

  • $\begingroup$ Grasping is not "an evolutionary afterthought" -- evolution uses no thoughts, and so can have no afterthoughts. Evolution has no aim in creating a variation; the variation either survives or it doesn't. $\endgroup$
    – mgkrebbs
    Nov 19 at 20:58
  • $\begingroup$ @mgkrebbs - I understand that. What I meant was that it seems that grasping does not seem to confer such an advantage that a grasping appendage evolves and is subsequently used for locomotion or other purpose. It usually is an appendage that evolves for locomotion that is adapted for grasping trees and then grasping food, etc. An octopus seems to not follow this pattern. Neither does an elephant, but an octopus took the adaptation further. $\endgroup$
    – mmesser314
    Nov 19 at 23:16
  • $\begingroup$ what about tails? i know a lot of animals use their tails for balance and agility. that's much more common than flexible limbs but probably results from the same evolutionary pressure to be agile. $\endgroup$ Nov 20 at 6:49
  • $\begingroup$ @AFriendlyFish - Good point. What about tails is another whole question. Social signalling. Horses use them as fly swatters. Apes, including us, lost them completely, but many other animals have not. Old world monkeys use them for balance. New world monkeys have prehensile tails and use them for grasping. What does a pig or a bear do with a little tail? $\endgroup$
    – mmesser314
    Nov 20 at 14:31
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    $\begingroup$ if you think crabs are clumsy with their claws you haven't watched them hunt. also animals that just try to bite their food don't do so well at it in open water, which is why so few animals do it. the closing of the mouth pushed food out of the mouth, which is why fish need some weird adaptation to suck in water or have really long sharp teeth to catch things before the water pressure change is large. $\endgroup$
    – John
    Nov 20 at 23:04


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