The spectrum on this planet really isn't all that vast. Sure, to you looking at an organism's morphology it looks vastly different, but so do dog breeds from eachother yet they are all dogs. You have a lot in common with all forms of life in terms of how your cell biology works, because we all share a common ancestor.

Life on another planet might originate from an ancestor that functions dramatically different than the last common ancestor for all life on Earth, and that might have huge implications for what a potential multicellular organism with this evolutionary trajectory would look like (if such life even utilized multicellularity, or cells at all)