Ammonite
Ammonites swam by jet propulsion, as do most other cepalopods. Water would have come into the mantle cavity, passed over the gills, and was squirted out. Nautilus also has an escape mechanism, where a contraction of the branchial (gill) chamber causes the animal to jump out of the way of a predator.p232 It would be reasonable to suppose that ammonites had a similar mechanism.