Uropods
These tail fan of uropods and telson is integral to inducing the rapid movement in the so called 'lobstering' escape reaction which occurs when the tail is flexed very quickly. The tail fan acts as a large paddle, pushing against the water beneath the crustacean and causing the animal to dart rapidly and unexpectedly (the a predator) backwards. This 'lobstering' is extremely energetic and using lobstering krill can race backwards at speeds of nearly 1 m/sec.