Septum (cephalopod)

Septa (singular septum) are thin walls or partitions between the internal chambers (camerae) of the shell of a cephalopod, namely nautiloids or ammonoids.

As the creature grows, its body moves forward in the shell to a new living chamber, secreting septa behind it.

The nature and structure of the septa, as with the camerae, and siphuncle, and the presence or absence of deposits, are important in classification of nautiloids.

In some nautiloids, such as the Orthoceratidae, the septa tend to be widely spaced, resulting in large, long camarae.

It is possible to calculate the strength of cephalopod septa on the basis of their thickness and curvature, and from this the shell's implosion depth can be estimated.