Real belemnites were extinct cephalopods (a group containing today's octopi, cuttlefish, and squid) which were part of a larger group called belemnoids, living during the Jurassic and Cretaceous periods. They were close relatives of today's squid, but they did not have tentacles and had ten equal-length arms with hooks which they used to trap prey. However, they were able to squirt ink, which was used to distract predators. The largest belemnites were 3 metres long. They were closely related to the ammonites, and became extinct with them at the end of the Cretaceous Period.