Belemnites

are an extinct group of squid-like cephalopods. They had 10 arms but no tentacles. The arms were covered with small hooks instead of suckers like modern cephalopods. They lived during the Jurassic and Cretaceous Periods. Belemnites had no shells like earlier nautiloids. Instead they had an internal, hard, cone shaped structure called a or guard. This is the part that easily fossilizes. Belemnites were quick and agile swimmers which made them efficient hunters. They ate fish and other marine animals. But they had to beware of Ichthyosaurs and other large marine reptiles who also hunted in the oceans of the Mesozoic Era. For a breif tutorial on belemnites watch this: