Here is a Liparoceras ammonite with just the body chamber preserved. Ammonites have a hollow, chambered shell, but the last half of the outer whorl is a long chamber with an open end through which the head and tentacles extended. Often, when the animal died, only the body chamber was filled with mud and the rest of the hollow shell was crushed flat as it became buried.
The image on the right is a close-up of the final chamber wall which is sometimes known as a ‘cat’s paw’ due to the superficial resemblance.
Find out more about ammonites on the molluscs pages.