Hm, I haven't touched the models in awhile. I used to draw tyranids all the time
though so I picked up a lot of things that were similar in all the species.
-5 head plates
-three oxygen holes (not sure if that's what they are, but there are 3 indents on each side) near the base of the tail
-5 basic body segments; head, ribcage, thorax (waist), hips, tail. The hips and ribcage are large while the thorax (where the abs would be) is generally smaller. Hips attach to tail.
-3 sets of limbs; arms, second set of arms, legs. All the arms are attached to the ribcage and the legs are attached to the hips.
There's a lot more, I just forget