I'd rank periphyton a bit of all three.
|It's fun watching the tiny fish|
and crayfish dart through the three-
dimensional sponge matrix
It looks like a plant (i.e. vegetable) when submerged ...
But once dry, it morphs into part of the marl soil below (i.e. mineral). Then there is the microbial organisms and critters that form and co-mingle in its sponge (i.e. animal).
Verdict: All of the above.