Europa, Jupiter or small planets offer different environments and gravity for alien life to evolve. I see many advantages to life possessing radial symmetry in both lower and higher gravity environments. What advantages and disadvantages would be pertinent to this form of life.

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    $\begingroup$ Bilateral symmetry evolved in the seas of Earth, and I expect that it would evolve in the seas of Titan too. Which is not to say that Titanic jellyfish and starfish wouldn't exist, but I wouldn't expect then to be any more dominant than they are here. $\endgroup$ – Arcanist Lupus Oct 23 '18 at 6:02
  • $\begingroup$ There's quite a few liquid environments here on Earth, and we certainly have critters with radial symmetry but they are far from dominant. Why do you believe that radial symmetry would have many advantages in higher/lower gravity? $\endgroup$ – Giter Oct 23 '18 at 14:13

I think you can look for an answer in Ediacaran biota, which, as far as I'm aware, lived exclusively in fluid environment. Just browsing through the list, there were a number of radially symmetric genera, but there is also bilateral and even tri-lobed symmetry.

Of course, Ediacaran seas are were shallow, and the fact that there was a bottom to be reached must have had a definite impact on morphology: if you can attach to something, or lie or browse along the bottom, that's a very different lifestyle than if you have thousands of kilometres of hydrogen atmosphere in every direction.

The benefits of bilateral body plan are organ specialization and mobility. Radial form lets you react to opportunities and threats from many directions. In other words, if you can predict where your lunch is coming from, go bilateral. If all directions are equally likely, radial is best. The same applies to others taking a bite out of you.

Would you have consciousness develop in radially symmetric creatures? I imagine that would produce vastly different minds from our own.


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