Septum (cephalopod)
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Septa (singular septum) are thin walls or partitions between the internal chambers (
.As the creature grows, its body moves forward in the shell to a new
Where the septum meets the shell a
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. In others such as the Ellesmerocerida, Oncocerida and Discosorida the septa are crowded closely together. In some straight-shelled forms like Actinoceras, calcium carbonate deposits extend from the camera (mural deposits) to the septa (episeptal deposits).
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. This has in turn been used to estimate maximum depth ranges for many living and extinct cephalopod groups, on the assumption that these animals would not normally venture deeper than two-thirds of their shell's implosion depth. Ordered by increasing depth, these estimated maximum depth ranges are: