jet propulsion This is the typical method of fast swimming in cephalopods. During jet propulsion, water is taken into the mantle cavity by expansion of the mantle. Water enters laterally at the sides of the head, passes over the collar, over the gills and leaves through the funnel when the mantle contracts. Mantle contraction causes water pressure in the mantle cavity to increase and forces the collar against the mantle wall. The collar, therefore, acts as a one-way valve to prevents water from leaving by the same route that it entered. The ventral wall of the funnel presses against the mantle during mantle contraction and seals that opening as well. Water, therefore, is forced through the funnel and out the funnel orifice. The force provided by the water leaving the funnel can be directed by movements of the funnel. Typically the water leaves the funnel anteriorly causing the cephalopod to jet backward (e.g. when escaping a predator) or the funnel is directed posteriorly causing the water to leave posteriorly and the animal to jet anteriorly (e.g. when pouncing on a prey). Some species are able to glide via this method. locomotion