Actinoceratida

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Actinoceratida (class Cephalopoda, subclass Nautiloidea) A large order of predominantly orthoconic cephalopods that have large siphuncles. Large amounts of siphuncular and cameral deposits are present. Most are assumed to have been nektonic. The actinoceratids ranged in age from Lower Ordovician to Lower Carboniferous.