Which evolved first: the mouth, the stomach, the digestive fluids, or the ability to excrete?

Question: Which evolved first: the mouth, the stomach, the digestive fluids, or the ability to excrete?
- Keywords:
  body,
  digestion,
  evolution,
  excretion
Asked by n3rdy to Gopal, Hannah, Becky on 27 Jun 2013.
- Hannah Little answered on 27 Jun 2013:
  
  That’s a really good question and i’ve never really thought about it before. Bacteria excrete stuff and they don’t really have a digestive system as we think about it and plants can also secrete or excrete waste and they definitely don’t have a mouth or stomach. I suppose all organisms that can excrete will do this through some kind of chemical process though, so probably digestive fluids came first.

Question: Which evolved first: the mouth, the stomach, the digestive fluids, or the ability to excrete?