bio-engineered living vessels
Now there's a thought, a bio-ship, I seem to recall reading a short story in some Sci-fi mag of old that refered to such a thing, and later I'm pretty sure one featured in a Dr. Who series. The name Dolan rings a bell??
I rather like the idea of something that was introduced by such a bio-engineered alien space vessel, a form of organic, bacteria laden contamination
if you like, that clings slime-like to any passing sugar molecules that happen to be orbiting a nearby star within a gas cloud of sorts and then maybe they might evolve a little bit?