Astrobiology: Evolution in a completely aquatic planet, your thoughts on how they would look like?

Question

In my anatomy class (for art) today, we had a discussion about the possibilities of evolution in other planets. Basically, astrobiology. Anyway, to get the point, I ended up wondering, should a planet be mostly made up of water (well, more than Earth's) and life were forced to evolve IN the water itself instead of our evolution theory from fish to amphibian to reptile, etc., what do you think the beings would look like having evolved completely underwater?

Would they look like the creature from the Black Lagoon, or Abe Sapien of the Hellboy series? Maybe Lovecraft's tentacled Cthulhu? Would they be half fish, like a mermaid of the Disney creations or a more fish-like being in the Harry Potter movies? Ofcourse these examples are just a joke, haha.

But what are your thoughts? Don't be afraid to wander in fantastic possibilities, just make sure it makes sense evolutionary-wise. And just to be clear, this is astrobiology, which is science, not magic and fiction.

Wow, okay, maybe I wasn't being clear. This is all speculation. Nothing anyone says will be regaurded as actual fact. I just meant for this to be some artistic fun among people who are interested in the possibilities of evolution and astrobiology, not what exactly WILL happend in any planet that's hospitable for life. Obviously we can't determine what the actual outcome would be.

And Joan, I don't understand your response. You said "we cannot begin to guess" on what otherworldly beings can evolve into, yet you say a humanoid structure is probably not possible in any other planet that has a potential of evolving like the Earth? That's a bit contradicting.

Answer 1

If development went in a similar fashion to Earth's, with the exception of the move to land, I reckon that plant life would develop to become the land.

Think about it - floating plants would recieve more sunlight than underwater plants would, they may even turn out to be like floral jellyfish, collecting scraps of food from the water. Give them enough time and enough cause to become larger - herbivorous creatures, possibly air-breathing life that develops to live on it above the surface - and they could develop into small floating islands.

Actually, that's not a bad idea for a fictional world *jots it down for later*

This concept is © Pirate Puppy 2006, no use without permission ;)

Answer 2

Most our evolutionary history happened in the seas. Everything happened in the seas until the revolutionary move of plants from the oceans to land. So you can just look at what happened before, oh, about 500 million years ago, and that'll give you a clue. Although it's really impossible to say; evolution is far too complex, and is unpredictable. In fact, it's been mathematically been proven to be unpredictable; Chaos theory was the result of studying evolutionary interations. Really, there is no scientific basis to any kind of this imagination, so just imagine what you think yourself.

Answer 3

As per the previous answer, most of the evolution of earth's creatures occured before life moved out of the seas.

As to the kind of life that might evolve on another planet, we cannot begin to guess. For instance, earth's life forms tend to be symetrical with pairs of many body parts like eyes, ears, legs, arms, fins, gills, wings, nostrils, etc. Would this happen on another planet? Probably not.