What's the most complex organism with a bi-directional digestive system? Are there any?

Question

I'm talking about an animal with a defined digestive tract (i.e., not unicellular) that can ingest food from either end and excrete waste from either end. If such a thing hasn't evolved (which I can't imagine it hasn't, so many other odd things have), would it be workable in a synthetic organism if you make an organism that needs to eat/excrete certain things? If so, what would work best as far as the kinds of things such an organism should eat/excrete?

Just curious. Very curious. About some of the darndest things. ;-)

Answer 1

The least complex multicellular organisms tend to have tidal guts. That is, the food comes in and the waste products go out, the same place. Unidirectional guts evolved for animals to be able to store food, and to allow animals to eat more complex foods, that take longer to digest. I don't know of any "bi-directional" guts, except that most animals can vomit the contents of their stomachs in some circumstances.