Wenlock nautiloids, like this Orthoceras, had straight shells; many other nautiloids, including those living today, have coiled shells.

Nautilus is the only surviving descendent of the many different groups of nautiloids found in the fossil record.

Nautiloids are related to ammonites, squids, cuttlefish and octopus, and belong to a group of creatures called cephalopods.

They have shells which are divided into chambers filled with gas. All of the chambers of the shell are connected by a tube which allows regulation of buoyancy by changing gas pressure inside the shell. This and a simple jet propulsion system allow the animal to move quickly and precisely.

The nautiloid animal lives in the largest outermost chamber of the shell. It has large, complex eyes, strong beak-like jaws and muscular tentacles.

Nautiloids are predators, feeding on smaller animals on the reef.

Nautiloids were reef dwellers, living in the cavities and crevices of the Wenlock Reef.

Abundance through geological time

Nautiloids first appeared in the Ordovician, and were very common up until the Permian. Most were straight-shelled; today only the coiled-shelled Nautilus survives.