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I can go into a little detail, I've researched a little online but feel my world is a slightly deviant case.

I'm trying to create life on a very hot, volcanic planet: one orbiting a gas giant, and with a large moon, so there is a lot of volcanic activity. I imagine a world, simply, with seas of magma, and small islands of rock.

I have creatures who use fire as there energy source, effectively finding fuel in the environment to set fire to, and power internal energy systems.

I'm having trouble figuring out how they would move (they be made of rock/or metal). I considered a system with legs made out of metal filings, using magnetism to control their movement, but seems like it would be very energy effiecent.

Edit: So, I'm creating this in an (alternate) world where life is an inevitablity, so it finds a way. I'm looking for a way that some rock/metal based 'creature', using fire as a fuel source, would be able to evolve movement. Wheels was simply an idea, apologies for confusion in question.

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    $\begingroup$ "animals with no biological parts" are not animals in our standard. And we have no idea about evolution in conditions you described (except extremophiles but these are way simpler and not metallic) $\endgroup$
    – Mołot
    Commented Oct 17, 2016 at 13:54
  • $\begingroup$ I think these creatures could be balloon-like sacks of gas, floating above the lava. $\endgroup$
    – AndreiROM
    Commented Oct 17, 2016 at 14:33
  • $\begingroup$ @AndreiROM i thought about it too. Probably more like a "plane" / "bird" looking animal that would permanently be flying, thanks to hot winds or eruptions. $\endgroup$
    – Strannch
    Commented Oct 17, 2016 at 14:50
  • $\begingroup$ Answer in video form: Why Don't Any Animals Have Wheels? by Vsauce $\endgroup$
    – Philipp
    Commented Oct 17, 2016 at 15:03
  • $\begingroup$ floating/flying creatures isn't something I had considered yet, thanks for the suggestion. $\endgroup$
    – user28207
    Commented Oct 17, 2016 at 15:58

2 Answers 2

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If the creatures are living on a fiery moon orbiting a Gas Giant, the analogue is Io orbiting Jupiter.

enter image description here

The intense radiation fields, the flood of energy being emitted from the Gas Giant itself and the electrical "Flux Tube" created by the moon cutting through the huge magnetosphere of the Gas Giant provides an energy rich environment. In the case of Io, constant geoflexing caused but the passage of multiple moons in resonant orbits also keeps the core molten and powers a violent geological process. Io is the most volcanically active body in the Solar System.

How any living creature could evolve in that environment will be up to you, of course, but chemical energy (i.e. "fire") is probably not going to be a part of it. The creature will somehow be utilizing the radiation or electrical fields in the environment instead in order to gain energy. One possibility would be to envision a creature with a multitude of "antenna" to receive the energy. The spiny sea urchin might serve as a model

enter image description here

Sea Urchin

The spines would serve a multitude of purposes, including receiving energy, acting as sense organs ("looking" at modulations in the external energy fields), communications organs (broadcasting information to other members of the species) and "limbs" (walking along the surface by moving the spines). The interior of the creature will probably not have analogues of mouths or guts, but may well have a "heart" and circulatory system to move electrolytes around the creature and act as a cooling system.

How such a creature would evolve beyond that point to use tools or become intelligent is difficult to imagine, but this provides a starting point.

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Hmm... Sounds like your environment might be good for something that used something like a Stirling engine (https://en.wikipedia.org/wiki/Stirling_engine) or at least something using that cycle. Basically, a Stirling engine runs off a temparature difference (via heating and cooling gas, which expands/contracts) - I used to have a little model one that would run off the heat from your hand, a hot drink, or warm sunlight. The engines With hot lava/ground and a cooler atmosphere, you could probably get a decent amount of power out of the temperature difference between the hot bottom and cooler top (with a cooling radiating surface?) of the creature. That might also help them to move - you could use hot/cold air to inflate/deflate bladders for a pneumatic style movement. (See this about an artificial pneumatic octopus from Harvard https://www.youtube.com/watch?v=69EgjZ__1Zw).

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