Telson

This is used as a paddle in the caridoid escape reaction ("lobstering"), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards.

In the Isopoda and Tanaidacea (superorder Peracarida), the last abdominal body segment is fused with the telson, forming a "pleotelson".

[3][4] The chelicerate telson can be clearly seen in a number of fossil species (like in eurypterids) and in extant animals (like the horseshoe crab "tail" and the scorpion sting).

][5] In millipedes, the telson consists of a legless pre-anal body segment (which may contain a posterior extension known as an epiproct), a pair of anal valves (paraprocts) or plates closing off the anus, and a plate below the anus (hypoproct), also known as a subanal scale.

[6][7] In centipedes the telson is the hindmost body segment, posterior to the genital openings, bearing two anal valves.