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?