Splitting a complicated mesh in half

I am working with a fairly complex model of a spider creature. I need to split the main body (in white) in half along the spine. It is a closed mesh. I was able to use the mesh boolean difference tool to subtract a small extrusion to cut the legs from the body. However when I use the same tool on the body it does not work. Split does not work. Tried a subtract a half of the body. Any ideas?

Hello - if the mesh is valid and for not have any non-manifold edges, a plane through (CutPlane) and MeshSplit should, but may not, work - the best next step is to try in the V7 beta, which has much improved mesh intersection code.