Ammonites

Devonian to Cretaceous. Only fossils remain. The outer shell of the coiled or straight compartment has a marginal tube, and the end chamber is protected by a keratinous plate or two calcareous plates; the partition wall is wrinkled; the sutures are complicated; the outside is carved.

The general term for all species of the phylum Cephalopod. There are about 650 species in existence, all of which are seafood, such as octopus, squid, nautilus, calamari, etc. From near shore to far sea, from the surface to depths below 4,500 meters. Low-salinity water is rare. Baltic water has low salt content and no cephalopods, but the Suez Canal has them. There are more extinct species than existing species, peaking at the end of the Paleozoic and Mesozoic, the most well-known such as ammonites and arrow stones. Cephalopods and gastropods are closely related.