This is one fossil, split in half and polished to reveal the hidden living chambers that once housed a predatory mollusk. This particular specimen is a compact size, with open chambers partially filled with minerals and crystals. The shell is so thin it is actually translucent! Ammonites were predators that resembled a squid with a shell. These cephalopods had eyes, tentacles, and spiral shells. They are more closely related to a living octopus, though the shells resemble that of a nautilus.