Evolution, that ingeniously subtle engineer, designed cephalopods such as squid and octopi to exploit the principle of jet propulsion for movement. These creatures propel through water at surprisingly high speeds – in the case of squid, more than 25 miles per hour.
They do it by squirting fluid out of their bodies, which in keeping With Newton’s Third law of motion, exerts an equal and opposite force on the cephalopod itself. First, the animal expands its muscular body cavity(know as the mantle), pulling seawater in through an opening near its head. To build pressure in the mantle, the marine creature closes off all orifices except its tube – like funnel, whch it can aim. Then, with a vigorous contracton of the mantle, the cephalopod forces water out through the funnel, shooting its own mass in the opposite direction – wheather away from a threat or towards its next meal.