As for the nucleus, I don't think the nucleoplasm would function nearly as proficiently enough if it were stretched into a torus, if that is even possible at all (which I doubt).
Rather, I suspect that it would have to have the cytonuclear and cytoskeletal systems similar to a xenophyophore, with different specialized nuclei and centrioles for certain locations.
I suspect this could be fixed by modifying the digestive system. Perhaps a specialized glycocalyx or cilia of some kind lining the diametric lumen that, when stimulated, releases digestive enzymes. On the upward and downward curves from the lumen to the outer surface area, the osmotic sites would be located; such that the subparticulates from the digestion and any additional subparticulates in the environment are directly absorbed. In this situation, the microorganism would actually be specialized for environments where macroparticulates can easily get wedged into the diametric lumen.
The anatomy I have in mind would be a bit too large for capillaries, which would likely cause some problems if it got into your bloodstream at all.
I'm not saying it doesn't, I simply find it a fascinating topic.
What are your thoughts on my propositions so far?