Telson

The telson is the last division of the body of a crustacean. It is not considered a true segment because it never carries any appendages. Together with the uropods, it forms the "tail fan" of lobsters, shrimp and other decapods. These are used as a paddle in the "caridoid escape reaction" (lobstering), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards. Krill can reach speeds of over 60 cm per second by this means. The trigger time to optical stimulus is in spite of the low temperatures only 55 ms.