The Rise of The CephalopodsNew animal forms developed, too. The cephalopods became the dominant predators of this period. Cephalopods are a group of mollusks that are related to octopus and squid.The orthoceras was a straight-shelled cephalopod that lived in the largest open end of its shell. Its feet came out of its head! They could rise and fall in the ocean water like a submarine. The siphuncle was a tube in the center of the animal. When filled with air, the animal’s body floated upward. A burst of air out the back end of the siphuncle pushed the animal forward.

Other Invertebrates
Brachiopods were also new in the Ordovician period. Brachiopods look like clams, but they do not belong to the same family. A brachiopod’s shells do not match. If you look closely, one shell is slightly larger at the hinge. The shells themselves each have bilateral symmetry. Clam shells have identical hinges so their shells are not symmetrical.

The plant life of ordovician period