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Context

I'm building/designing a set of creatures in a world I'm making. Currently the creatures I am designing will live in an extremely hot, dry desert. About the same amount of rainfall as the Atacama Desert but far bigger. The creatures evidently have to store water so one idea I had was that I could have an animal that is pretty much a perfect sphere to minimise water loss.

My question is how could such a creature move?

Criteria for success

  1. The creature must be fast enough to evade predators.
  2. Movement should take up as small an amount of energy as possible.
  3. The creature must be able to move on sand and rock.
  4. The creature must remain as spherical as possible

Bonus points for coming up with a name for the creature.

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Why, hello there! I'm a Roksphere. I'm spherical, to protect myself against the harsh conditions of the desert, but I need to get around. I don't have any limbs. Instead, I propel gases out of one of my sides. Here's a diagram:


Most body parts not shown.

I have six holes, with two along each axis. I also have a large central chamber inside me, filled with carbon dioxide. When I want to move, I use strong muscles to propel it out of one of the holes - the other five remain closed with flaps - which generates a torque. This then makes me roll!

I'm kind of like a furry rocket, but I look much cooler. Plus, I can turn nearly instantaneously.

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    $\begingroup$ a remark: propelling gas with some sand in it (which is easy to get in a sandy duney desert) can increase push force compared to just gas $\endgroup$ – user1306322 Jul 10 '16 at 0:02
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    $\begingroup$ @user1306322 Interesting idea, although I'd be worried about damage to the creature's internal organs. $\endgroup$ – HDE 226868♦ Jul 10 '16 at 13:52
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    $\begingroup$ @HDE226868 I'm more interested in damage to some other creature's organs ;-) $\endgroup$ – John Dvorak Jul 10 '16 at 18:53
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    $\begingroup$ I'd add more thrusters, though, if they are going to be off-center. An alternative design with six on-axis thrusters is possible, but I feel it might be less efficient. $\endgroup$ – John Dvorak Jul 10 '16 at 18:59
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    $\begingroup$ How does it eat? $\endgroup$ – Xandar The Zenon Jul 11 '16 at 4:48
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This animal already exists... somewhat. Its an armadillo. Armadillos are found in arid environments as well.

An armadillo-like animal would be able to roll around. But since it can it can unball itself, it can do so much more. Digging, fighting, climbing, the Macarena, and high fives.

We shall call it the, deserillo.

enter image description here

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  • $\begingroup$ Now I want to see an armadillo doing the Macarena. $\endgroup$ – Hankrecords Feb 26 '18 at 11:16
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Start with a kangaroo rat. Picture for reference:

Add to it an instinct to how to roll like a human would:

Mae Ukemi forward roll

With the advantage that it can use its tail for propulsion (by pushing the body forward on every rotation), balance and turning.

Now since it's going to store more water than it already does in nature (which is a lot... these animals are more water-efficient than camels), and move by rolling, natural selection will naturally pick the rounder ones on each and every generation. They will look more and more like pokémon, and may even end up losing their legs.

You can call the species Ukemi waza. That sounds scientific enough, and is actually a japanese umbrella term for martial arts rolling techniques in general.

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    $\begingroup$ Nice concept and I can see how it could evolve. My one problem is it might have trouble turning. $\endgroup$ – Bellerophon Jul 9 '16 at 21:59
  • $\begingroup$ @Bellerophon it oculd use its tail for that. $\endgroup$ – The Square-Cube Law Mar 26 '17 at 13:56
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This idea isn't especially sensible, but it meets your criteria. Kinda.

Start with a tortoise. Make it more spherical. Give it a set of bladders for water, in compartments of its shell. Make it able to pump the water around between bladders rapidly. The transfer of weight lets it roll.

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  • $\begingroup$ Where will it find enough spare water in a desert? $\endgroup$ – Bellerophon Jul 9 '16 at 22:00
  • $\begingroup$ Water shortage is a problem, but changing the centre of mass is no problem; you have to swap water and air around in the bladders, and you do that with muscles, running off chemical energy from food. My centre of mass is moving as my evening meal makes its way through my digestive system; this hypothetical creature just does similar things faster. $\endgroup$ – John Dallman Jul 9 '16 at 22:23
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    $\begingroup$ You have reaction against the ground. That's the key. Consider water at the bottom of the sphere. Now the muscles pump it up the side, in the direction the creature wants to roll. That side gets heavier. If the contact with the ground was frictionless, the sphere would just spin in place. But it isn't frictionless, so the sphere rolls. $\endgroup$ – John Dallman Jul 9 '16 at 22:35
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BB8 from Star War Episode VII actually rolled in the desert and has a spherical design:

enter image description here

As discussed on SF.se, the prop is not an optimal design, nor do we see the whole picture, e.g. supports for the prop such as a trolley. I think the best summary from that post is:

He was able to move in sand without skidding because there was much more to some versions of BB-8 than we see onscreen.

How does BB-8 move in the sand without skidding?

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One possible idea which also allows moving upward is that the creature can extend itself into an elongated shape, the same working principle in many perpetual motion machines.

Perpetuum mobile

Image: Wikimedia Commons, Creator Dims, License Public Domain, 2005-05-08

The fact is while it does not work as perpetual motion, it really works if the creature uses energy to deform itself; then it can be made quite efficient.

Spherical locomotion itself is not so crazy as people may think: The wheel spider rolls itself into a ball to roll down dunes for escape.

What I am missing is how the creatures itself can survive. The extremely arid Atacama parts are lifeless. So you need to give them an energy source, perhaps that the desert itself contains nutrients or chemicals which can be exploited by the creature.

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    $\begingroup$ Could you please indicate the source of that image? (Unless you created it yourself.) $\endgroup$ – ruakh Jul 10 '16 at 1:29
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This one is a little more unorthodox than some of the other answers, consider it a wildcard. I'm aware it's not spherical, but it fulfills all of the other criteria and actually negates the need to be spherical. The OP did say that being spherical was just 'an idea' so I assume (s)he is open to other possibilities.

I propose a plant-animal hybrid.

Meet the Chryvador. A play on the word Voador which is Portuguese for 'flying' and the feeling that any creature that looks like this should absolutely have some form of 'chrys' in its name.

Structure

A large but lightweight creature, not unlike the Extatostoma tiaratum (pictured) enter image description here

While the actual creature in the image is in fact an insect which pretends to be plant to hide from predators, the Chryvador would have far larger 'leaves' with the ability to act as sails, so it is carried by the wind but is able to control its direction in a similar manner to that of a sailing boat.

Survival

The Chryvador does not need to store a lot of water, only around a day's supply at most. It has a sharp and extremely long extendable tongue which can penetrate the ground rock and down into the water table several meters below the surface and extract the water it needs to survive in a similar way to a tree root. If approached by a predator while 'drinking' it can save time by detaching its tongue and taking off immediately; the tongue will grow back in a matter of hours so while it is possible, it uses a lot of energy and is not desirable to do this regularly.

Lifestyle

Generally living in groups of between twelve to fifteen, they will display behavior not dissimilar to that of the Meerkat. To extract enough water from the ground below the rock a large amount of time will need to be spent doing this. Two or three will keep lookout while the rest perform this act. Every individual in the group will take its turn as lookout.

Ecosystem Quirks

As an additional defense mechanism, when a tongue is discarded it will continue to extract water on its own and at the top a plant will grow which is smaller and inert but looks very similar in appearance to a Chryvador. These are left in place for two reasons. Firstly they are useful decoys. But secondly they provide a source of nourishment for other nomadic creatures. It is often in the interest of these other creatures to scare off the Chryvador but not actually kill it, as this provides them with a regular source of food and water for themselves. These creatures will actually defend the Chryvador from animals seeking to eat it, as that would essentially cut off its own food supply.

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    $\begingroup$ I kinda like your idea and, although I will stick with the Rocsphere from above I will definitely also use your creature in my world. $\endgroup$ – Bellerophon Jul 10 '16 at 10:19
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HAMSTERBALL!

enter image description here From dubaipetfood.com

In this version the round part is a shell. The animal constructs it with local materials and sticky spit, like a caddisfly case.

enter image description here

From http://twistedsifter.com/2013/03/caddisfly-larvae-cases/ these caddisflies were provided some pretty high end building materials.

The creature dwells inside its constructed case and roves around like a hamster in a ball. It can open a hatch to poke its head out and feed or poke its excretory organs out and excrete. Maybe it would leave the ball to mate but not necessarily. It can leave the case entirely should circumstances warrant. It can repair the case if damaged or enlarge it as it grows. It occurs to me that a case that incorporates something distasteful (for example the predator's own feces) would be a good defense against being eaten, at least by things that do not like messing with their own feces.

I wondered if a hamster ball could roll on sand. I found video of a spherical robot cruising around on sand. It looks like it has projecting linear treads. https://www.youtube.com/watch?v=5mvr--XEeT4

The critter is a Kugel. Why Kugel? "Sphere" in German. Why German? Because "Kugel" is an awesome name.

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  • $\begingroup$ I really like this idea. It's definitely my second favourite idea after the roksphere. $\endgroup$ – Bellerophon Mar 26 '17 at 11:25
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Idea: The creature is covered in an exoskeleton, and it uses muscular contractions in order to push out plates in a spring-like motion. Its exoskeleton is also smooth, reducing friction and increasing movement speed and efficiency. These plates are positioned at equal distances from each other, and there's at least 4, so that it doesn't end up upturned and unable to move.

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