If you remember what a nautiloid is, then you have a pretty good idea what a goniatite is. Like nautiloids, squids, and octopuses, goniatites are cephalopods. They are members of a larger group of cephalopods called ammonoids. Like nautiloids, ammonoids were protected by hard shells. Their shells ranged from coiled to straight.
Some ammonoids swam in the sea, while others lived on the seafloor.
The animals that lived inside ammonoid shells were probably more similar to squids and octopuses than to nautiloids, however. Like squids and octopuses, ammonoids had an ink sac, for example. Ammonoids are classified into three groups by the sutures that hold the segments of their shells together. With their zigzag sutures, goniatites were the first ammonoids. They were established by the Middle Devonian Period and survived for 170 million years.