Telson n. : The terminal joint or movable piece at the end of the abdomen of Crustacea and other articulates. See Thoracostraca.

Example:
hi!!i have scorpion and i noticed that his Telson is missing! is my scorpion gonna die?

Taxonomy
telson, free encyclopedia, tail fan, Ruppert, Lauterbach, segments, search, Diagram, body, embryo, teloblast, carries, furca, paddle, lobstering, flexes, dart, D. Barnes.

Defination from the web:
telson forms the tail fan of lobsters, shrimp and other decapods. ... The same term telson is widely used (e. g. invertebrate textbooks such as Ruppert & Barnes, 1994 and Brusca & Brusca, 2003) for the caudal spine ...