Here is a fossil I found years ago that I always wondered what it was. While in the library the other day I found out what it was. It is part of crinoid called ancyrocrinus and what that part is the bottom of the crinoid. It was like a weighted grappling hooks or an anchor that would drag along the sea bottom until it got snagged on something. The top part would have the stem and the calyx. So this crinoid was mobil.
This fossil only has one hook left. The other three and the stem are broken off.