I call this piece shell as it suggests a shell form with the angled its around the side and the spiral form in the middle. It is one of the pieces influenced by looking at New Zealand forms. The spiral form is common in many of the souvenirs and the angled pieces were on at least one structure we saw there. It is a common form in Maori art and I have used the form with my own interpretation..ie. the junk materials.
It suggests to me that as the shell is often created by secretions( offcasts) of the body to protect the animal inside so this spiky form protects the beautiful curves of the inner shape.