Cephalopod
There are at least 800 different living species of Cephalopods. Two important extinct taxa are the ammonites, and the belemnites (order Belemnoidea, of class Coleoidea). Cephalopods are found in all the oceans of the world and at all pelagic levels. None of them can live in freshwater (water with no salt in it), but a few species live in brackish (partly salty) water.