Has anyone made sentient species that use cell mouths?

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.