Belemnites belong to the subclass Coleoidea, and they were numerous during the Jurassic and Cretaceous periods. They are an extinct group of marine cephalopods, similar to modern cuttlefish and squids.

The typical belemnite possesses a shell without a living chamber, and consists of three clearly defined portions:

  • phragmocone: portion of the shell divided into gas chambers

  • guard(rostrum): a massive, bullet-shaped cylinder of solid calcite; is parallel-sided and tapers posteriorly to a point

  • proostracum: a long, flat, expanded tongue projecting forwards and presumably covering the anterior part of the body, the proostracum is rarely preserved and hence, its function is poorly understood

Figure 23: Morphology of a belemnite.

Specimens with eight radiating sets of hooks have been found, testifying to the former presence of arms, and even fossilized ink sacs have been located in place.
Figure 24: A rare impression of the tentacles of a belemnite.
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© Sarah Vandervlugt.1998