Jigsaw critters with two brains
Picture a creature that is basically a jigsaw puzzle - multiple parts, but those parts are shaped in such a way that they "snap" together and are unable to be pulled apart without deforming them. If the spaces between the pieces are relatively large, but smaller than the curves and angles holding them together, it is possible for a 2D creature to have an anus and a circulatory system.
What is particularly interesting about such a body shape is that each "segment" of the body will have a separate nervous system. This may mean that each creature has two (or more) separate brains that work together, or it may be possible for it to have nerves that can actually split apart and re-join.
