(If you're interested, now would be a good time to scan the Wikipedia master list. I'm sure they haven't gotten everything, since I don't see any record of the Quintaglio on it, but it gives a nice overview, at any rate. Note that Star Trek, Star Wars, Farscape, Babylon 5, and Doctor Who are responsible for a lot of the species.)
I remember being intrigued by the idea of the Quintaglio. Far-seer was the first time I'd encountered sentient non-humanoid aliens, and let's face it, a book featuring a dinosaur civilization? Pretty darn awesome. The Prawns in District 9 hit me the same way: "Holy mother of Asimov, they did that?"
Thing is, I want to be wowed more often. I want every book/movie about aliens (or every other one, I'm generous), to give me the same feeling. I want more creativity! Humanoid aliens are sooo last century.*
Alien molds that haven't been done, that I know of:
- Octopus (real octopusses octopusi ones, not aquatic things with tentacles)
- Bacterial hive-minds
- Slime molds
Or we could follow the route laid down by Stargate, and go with deities. A race of satyrs, perhaps? Trolls? Chinese dragons? Western dragons? The Hindu pantheon? The Mayan gods? There are an awful lot of folkloric and mythological monsters, not to mention the ones that popped up in medieval travelogues and the like.
Let's not forget that our minds are influenced by our experiences and cultures. Some writers have created beings that don't match neatly to an Earth-based lifeform or concept, but most build on what we know about the natural world already. What if we went beyond that? What if we built a planet or environment first, and then evolved a species to survive in it? After all, there are some very extreme lifeforms on our own planet.
One possible environment, "close" to home: the diamond oceans of Uranus and Neptune.*** This would be a rather hot, very high pressure place to live. There probably wouldn't be a lot of gas mixed into the diamond, let alone oxygen, so either the aliens wouldn't breathe, they'd use a system like photosynthesis where they'd break down carbon for energy, or they'd be like whales, surfacing to breathe hydrogen, helium, or methane (those being the abundant gases). The aliens would almost certainly be carbon-based, and would consume other carbon-based life for energy. They'd likely evolve something like fins or flagella to propel themselves. Maybe they'd use jet propulsion.
I doubt that these aliens would achieve buildings, because short of building on the solid-diamond floes, there'd be nothing solid, and the caps probably wouldn't be all that stable. However, they could still have a civilization, of sorts. Dolphins and whales have proto-languages. Octopuses use tools.
Actually, I can see floating, roundish structures tethered together into cities, provided the aliens had something to build with. Perhaps after millennia of them using these structures, they'd adapt to them, becoming more amphibious than aquatic or losing the flippers and gaining something more like hands.
Perhaps not. They'd still be cool.
What about aliens living in nebulae? Black holes? Asteroids? Stars? It's not entirely impossible. Think of what our descendants (or even ourselves) could discover!
* Just my opinion. Go ahead and prove me wrong.
** Yes, yes, they're technically fish, sue me, a civilization of sharks would be wicked†
*** Boing Boing
† I just dated myself, didn't I?