The species is the smallest category in classification. Species form a genus, genera a family, families an order, orders a class and the classes are combined into phyla. Several intermediate steps in classification are inserted to clarify the complexities of animal or plant relationships. The class may be divided into sub-classes, each containing several orders; or a family with other families may constitute a superfamily. An order may contain more than one superfamilies. The criteria of other intermediate steps (such as superorder, infraclass, etc.) are not established.