Here's another sketch I did a while back. This takes place in an oceanic environment on an alien planet. I need to define these creature's roles exactly, but at this point the central "hub" (with radiating spokes with spheres at the ends) is a colonial creature. The ones at the top are filter feeders, and the bottom ones are an example of convergent evolution- although completely unrelated to earth's fish, similar environmental forces have shaped them into a similar form.
I've recently been working on several more sketches which are ready to be turned into full-scale illustrations as soon as I find the time.
Would be interesting to see an ecosystem like this in some kind of thick, soupy nebula, not that that would really be possible to the best of my knowledge.