There is a creature. Let's call it a Blop.
Blops are fairly simple creatures: They consist of a tough, flexible outer skin and then an inner structure that is (essentially) organs and tentacles floating in goo. This gives them a remarkable versatility, as they can literally flip end-to-end within their own skin, or push their organs through a small space one at a time while remaining safely intact. They can best be thought of as the unholy offspring of an octopus and a honey badger.
Respiration is fairly simple: Blops are amphibious swamp dwellers, so a semi-permeable skin allows them to breathe and exhale simultaneously. The issue that I'm having with the Blops is that they are relatively high-energy creatures (they burn a lot of calories), and so have to actively consume other carbon based material in order to survive (Don't worry too much about what they're eating. If you're assuming a certain kind of biomass just note it in the answer)
Given that the Blops have an outer skin with no orifices and can be at any orientation within said skin, how can they eat and defecate?
One last thing: Ideally a Blop should be able to eat while on a person's shoulder (I'm not planning any space piracy. No sir! Not me!), but it isn't required.