They could use sight or smell (though the latter is unlikely with the smog and all). Think bioluminescence, like deep-sea critters.
A planet entirely covered in smog, if it had life at all, would lead to very, very alien aliens. As in, more different to us than even-non animal life, like plants. I find it kinda odd that the smog would be toxic to anything that evolved there.
edited 19th Mar '11 9:19:23 PM by RTaco
I second the above. They probably have a complex system of sign language, expressions and gestures. Carrying this across to other races, however, might prove to be problematic.
I've returned from the depths to continue politely irritating the good people of Tv Tropes.(◕‿◕✿)We speak because air rushes past our vocal chords, which in turn vibrate and produce sound.
Why not simply have organs that act like vocal chords, but instead twitch and vibrate without the need of air? They would sort of behave like muscles. That way they can produce sounds without needing air or even a mouth. (The sound would be loud enough to be heard from the inside of the body... sort of like a gurgling stomach.)
Just an idea.
edited 21st Mar '11 5:39:23 PM by somerndmguy
Just as a note, if they have their own vibrations they will not even remotely sound human, nor could you really map any sounds they make to an alphabet—unless they were in such control of their modulations they could replicate human language like a speaker output doing the same.
In which case, their sounds would be so varied they would likely have very dense languages.
The Starfish Language idea sounds good, yes.
As for the alien's body shape, I'm going to have them as Humanoid Aliens, but with as much variation as possible, so they are a Humanoid Abomination for Starfish Aliens. Like, elbows that bend in ways they shouldn't, A bigass toothy maw for a face, Uncannaly long limbs,things like that.
edited 26th Mar '11 11:43:22 PM by doorhandle

Alright, so I have this species of evil Buddhist-like Death World Aliens that don't need to breathe, and instead make all the energy they need to live though [[http://en.wikipedia.org/wiki/Anaerobic_respiration
Anerobic Resperation].](With their space their lungs took up being replaced by a pair of organs dedicated to processing lactic acid/manufacturing sulfur.) This adaptation occurred in all creatures on their home-world, because the disgusting smog that passes for air there is too full of pollutants and unwanted chemicals to breathe and anything that would try would be poisoned or suffocated within minutes.
This is all well and good, even if it fails biology a little, but I have come upon a problem: How the hell would they talk? It's not like they would have windpipes or anything!
By the time the story rolls around, they would all have masks with inbuilt vocalize-machines and translators, but first I need to know how they communicated in the first place before those were invented.
Any ideas? And any other ramifications of a planet covered entirely in volcanic smog?