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Nautilida (class Cephalopoda, subclass Nautiloidea) The only present-day order of nautiloids, whose extant members are involute nautilicones (see NAUTILICONIC). The majority of nautilids have a narrow siphuncle in a subcentral position. Sutures vary from simple to very complex. Nautilus is the only extant genus. The order first appeared in the Middle Devonian.