Cephalopods are a higher class of the fossils of the phylum Mollusca. Modern squids, octopuses and nautilus fall within this class. Cephalopoda get their name because they have circular tentacles in their head used for hunting, crawling and swimming. All Cephalopoda lived in marine environments. They began to emerge in the Late Cambrian and have lived until the present day, and they are widely distributed. These fossils are important index fossils. Nautiloids and ammonites are cephalopod fossils of high ornamental value. China is rich in Cephalopoda - Armenoceras fossils. Typical examples are the Ordosoceras, Armenoceras, and grey Armenoceras in the Ordovician strata in the north and the Sinoceras, Discoceras and Michelinoceras in the Ordovician strata in the south.