Nautilus belauensis seen from the front, showing the hyponome. The Palau Nautilus ( Nautilus belauensis) is a species of Nautilus native to the waters around the Pacific Island nation of Palau

The hyponome or siphon is the organ used by cephalopods for locomotion. The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by It is a muscular funnel or siphon into which water is drawn. A funnel is a pipe with a wide often conical mouth and a narrow stem A siphon (also spelled syphon) is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher than the reservoir the flow being The hyponome expands and then contracts, sending a jet of water rushing out. This jet propels the cephalopod backward, but it can control its direction of movement by pointing the hyponome in different directions.

The hyponome of the nautilus differs from other cephalopods in that it is a one-piece flap that is folded over. Nautilus (from Greek ναυτίλος, 'sailor' is the common name of any marine creatures of the Cephalopod family Nautilidae, the sole In other cephalopods, such as octopus, squid, and cuttlefish, the hyponome is a muscular tube. The Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species Cuttlefish are marine animals of the order Sepiida belonging to the Cephalopoda class (which also includes Squid, Octopuses The flap-like hyponome may be an adaptation to confinement in a shell that both nautiloids and ammonites shared. Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum