Squid are members of the phylum Mollusca , soft-bodied animals that inhabit mostly fresh water. Molluscs are characterized by a similar body plan consisting of the mantle,visceral mass and foot .
While the foot is usually used for movement, the visceral mass contain most of the internal organs and the mantle is a heavy fold of tissue draped over the visceral mass.
Beneath the mantle is a water-filled chamber which houses the gills, anus and excretory pores.
This is known as the mantle cavity and it is used in locomotion.
Squid swim using jet propulsion and undulating fins, using the latter to steer in different directions.
Drawing water into their mantle cavity by contraction of muscles in the mantle wall and expelling it in a jet stream near the anterior, squid appear to dart about and usually backwards.
They are able to propel themselves in various directions by directing the jet stream.
When in danger and escaping from predators, squid also display a behaviour known as escape jetting .
They do this by first hyperinflating the mantle then contracting it powerfully, so that water in the mantle cavity is exlelle d at a greater force