the species and family concerned, some bivalves utilize their inhalant siphon like the hose of a vacuum cleaner, and actively suck up food particles from the marine substrate. Most other bivalves ingest microscopic phytoplankton as food from the general water supply, which enters via the inhalant siphon and reaches the mouth after passing over the gill. Please also see pseudofeces. Hyponome of cephalopods The hyponome or siphon is the organ used by cephalopods to expel water, a function that produces a locomotive force. The hyponome developed from the foot of the molluscan ancestor. Water enters the mantle cavity around the sides of the funnel, and subsequent contraction of the hyponome expands and then contracts, expelling a jet of water. In most cephalopods, such as octopus, squid, and cuttlefish, the hyponome is a muscular tube. The hyponome of the nautilus differs however, in that it is a one-piece flap that is folded over. Whether ammonites possessed a hyponome and if so what form it may have taken, is as yet not known. References External links Glossary Bivalve anatomy More bivalve anatomy Bivalve anatomy Cephalopod zootomy Gastropod anatomy Invertebrate respiratory system Articles containing video clips