by using jet propulsion
Celphaopods use jet propulsion by sucking in water and pushing it outward with extreme force.
Squid and octopus are "cephalopods" if in a hurry they squirt a jet of water to propel themselves but some can crawl around on the bottom of the ocean too.
They take in water and shoot it out behind them like a jet.
By breathing your stomach goes up and down and also your heart is still moving.