The Ammonoidea constitute a subclass of extinct cephalopods found in marine sediments from the Early Devonian through the Cretaceous. Baring an external shell, ammonoids superficially resemble nautiloids, such as the modern Nautilus . however, based on similarity of the radulas, they are more closely related to modern coleoids , squid, octopus, and cuttlefish. Ammonoids are commonly referred to in the vernacular as Ammonites, although the term is often reserved for members of the order Ammonitida. For derivation and history of the term see Ammonite