Cephalopod mantle muscle 2

The movement of cephalopods is driven by the muscle contraction of the mantle. When the mantle ring muscle relaxes and the radiating muscles contract, the volume of the outer jacket cavity expands, and water enters the outer jacket cavity from the opening of the outer jacket cavity.

After the outer jacket cavity is filled with water, the radiating muscle relaxes, the annular muscle contracts, and the locker closes the outer jacket cavity. The opening of the funnel increases the pressure in the jacket cavity, forcing water to spray out from the opening at the front end of the funnel.

The reaction force pushes the body back quickly, and there is a free tongue-shaped valve in the funnel, so that water can only be ejected from the funnel mouth and cannot flow in from the outside. If the front of the funnel bends backwards and sprays water, its reaction force pushes the body forward. Under normal circumstances, animals such as squids have more force when the funnel sprays water forward than backwards. Therefore, the backward motion of cephalopods is faster and more common than forward motion. Especially in long-distance swimming, it is more commonly used to retreat.