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I am working on an alien species which have tentacle like appendages along their limbs, based on the range of appendages used by marine suspension and filter feeders.

On land, many of the species have lost the limb protrusions, some just have spikes in their place but one species due to complex mating displays has kept the tentacles and has learned to move them with great precision.

As this species will be the advanced species on the planet and will take a similar path as humans to advance into a technological civilization, I will pose this question as if humans had these tentacles.

The tentacles will run along the outer sides of the limbs, they are around 10cm long with full range of motion, each tentacle can hold onto up to 5kg and each limb can have 10-15 tentacles running perpendicular along its length.

My question is: Would these limb tentacles aid a human in daily life activities? I can image a few activities such as multitasking simple tasks close to the body, carrying light or slender items using single or combined tentacles but I am not sure about other tasks that would make them useful enough that they would keep them as the species advances, if not they may reduce in size and disappear like the majority of other the species.

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    $\begingroup$ Is this scenario tentacles in addition to fingers? Or tentacles in addition to some blunt ended or otherwise specialized limb? Our fingers are tentacle-like. We can do things with our limb tentacles that the dog and seal cannot. $\endgroup$
    – Willk
    May 29, 2022 at 14:04
  • $\begingroup$ @Willk Yes in addition to fingers. They could do all the things we can with our fingers but running along the outer side of the limbs are these tentacles. $\endgroup$
    – user96146
    May 29, 2022 at 14:10
  • $\begingroup$ Lift 5Kg? Those are pretty big strong.appendage. That would be more then enough to wield a short sword. Big enough to wonder at the leverage issues. $\endgroup$ May 30, 2022 at 19:22
  • $\begingroup$ @GaultDrakkor Yeah that number and other details need more thought. I based it on what weight plate I could hold with my little finger without too much discomfort for a period of time. When I thought about the tentacle uses it was more multitasking with light items/tools, button pressing etc not for heavy lifting. $\endgroup$
    – user96146
    May 31, 2022 at 12:38

2 Answers 2

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Very.

The backpack has been around for ages, and people often imagine it will continue that way. There's a scene from one of the Star Wars movies with future Darth Vader hauling one. Nonetheless, there has been some technical progress: the good hikers say that a proper modern backpack frame transfers the weight to your hips instead of your shoulders.

Your people do much better. They carry the items they need all over their body, each at the ready. When they have something very big, it simply has multiple tentacle-holds.

They can also link up to one another, whether to carry the wounded around without a stretcher or to make an "ant bridge" across a chasm. 5 x (10 to 15) x 4 = 200-300 pounds of carrying capacity plus the limbs, so they probably can each securely grasp an edge while confident of their hold on another person suspended over the gap; they might also manage a fifth in the middle.

The tentacles may also allow them to creep in tiny steps across a surface without using their limbs directly, making them exceedingly stealthy, especially if they are also clutching and waving bundles of dry grass above them.

Simultaneous control of the tentacles would let them plant multiple furrows of crops at once, first poking the hole with one tentacle before dropping the seed with the one behind it, taken from a third that carries a pouch of them. They might be similarly competent at harvesting.

The catch is that all this is hard to do. Hard to provide a blood supply for strong muscle motions along the entire tentacle at once. Hard to control those by nerves. Hard to coordinate all those muscle motions from a brain. Hard to get visual data to guide where the tentacle can go, or to process the accompanying sensory data to feel the way.

I would be tempted to go the route of making the tentacles more autonomous, as octopi do. But this involves sacrificing some degree of control. Making tentacles easy to regenerate, giving them an eye for local sensory integration... might be nice. But for your organisms to do much, much more control and exertion than people, they need a more robust overall design of cardiovascular and nervous systems, with the rest having to keep up with those. You basically have to suppose they evolved better than us, which is certainly possible (older planet, better set of building blocks than amino acids, etc.).

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  • $\begingroup$ When you say more robust cardiovascular and nervous system, what would that entail? Stronger or multiple hearts? what changes to veins and nerves do I need to think about? $\endgroup$
    – user96146
    May 29, 2022 at 18:06
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    $\begingroup$ Moving a tentacle involves a lot of different muscles running different directions, which need to be directed from a larger mass of neural tissue. Some of that can be local. Sensation increases with the body size of an animal, and I imagine tentacles offering useful proprioception with tremendous surface area have a similar requirement. Octopi are described to have nine brains and three hearts, and your situation may be more demanding (more tentacles). $\endgroup$ May 29, 2022 at 18:42
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Climbing

climbing

The tentacles are used to climb shear surfaces. They work similar to a gecko's feet: The individual tentacles go into small cracks and then expand by filling with fluid to offer grip.

This is not a stretch when you consider similar microtentacles on starfish can expand and contract depending on whether the starfish is in air or water.

enter image description here

Your tentacle people cannot climb a stone wall like a gecko. But perhaps they can climb the trunk of a large tree by gripping the bark in several dozen places, with only a few kilos on each hold.

enter image description here

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  • $\begingroup$ Plus you can climb the tree "backwards" with your toes and face pointed away from the trunk. $\endgroup$
    – Daron
    May 30, 2022 at 14:03

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