This fossil comes from the Mulde layers, Silutian, near Djupvik, Gotland, Sweden.The trilobite fragments belong to Calymene tuberculata. However, the interesting thing about it is that the trilobite seems to be entombed in a shell of something else.
At first glance, I though it was a cephalopod because of its long tube like shape, which also makes sense because ceplhalopods feed on trilobites. But from the sideview, I can see that the shell is made of two halves, and there is no visible segments along the tube. And you can see curves from one side, which makes it look like a brachiopod. Does brachiopod eat trilobite? Or could it be a crushed cephalopod?
Does anybody have any idea about what it is? Sorry that I don't have tools to further prepare the fossil, so the shell is still largely covered by the matrix.
The pictures below are showing topview, sideview and backview (trilobite is on the right).