Belemnites

Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related[citation needed] to the modern cuttlefish. Like them, the belemnites possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length, and no tentacles. The name "Belemnoid" comes from the Greek word belmnon meaning "a dart or arrow" and the Greek word eidos meaning "form".Belemnites were numerous during the Jurassic and Cretaceous periods, and their fossils are abundant in Mesozoic marine rocks, often accompanying their cousins the ammonites.