I would be interested in knowing how often people make sentient beings that use cell mouths as their only mouth when reaching tribal stage.
I recently watched a Youtube video from The Spiffing Brit where he did a full run without ever evolving at all. Still got DNA by "singing" to other creatures and eating generic food, but never added any parts onto his original cell-stage default creature. It just kept getting bigger with every levelup. So yeah, some people keep the original mouth I guess. It didn't seem to cause any problems for this guy, at least not on camera. The lack of any legs was a bigger issue though, he kept getting stuck on certain places on the terrain and some of the cutscenes just went a little bit insane because they were meant for creatures with legs. LOL.
It's normal for a creature/tribal stage thing to have cell mouths, and it works fine. The thing that breaks spore is having no legs. Try it and see, get to the tribal stage with a legless guy. Then do a campfire dance and watch everyone freak out and fly about.
many people have. the challenge is take it to the space stage; and then the captain stage.
create a cell with the most parts to use as a base to create other creatures from at a later date.