Telson:
Source: Wikipedia
The telson is the posterior-most division of the body of an arthropod. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked “tail” called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups. [Wikipedia]
Noted in “Meet Your New Nightmare: Ancient Spider With A Tail Preserved in Amber,” Gemma Tarlach, Dead Things:
Known from four specimens, the ancient arachnid’s formal name is Chimerarachne yingi. Its genus name, from the mythic Greek Chimera, is a nod to its unusual mix of features. There’s that one feature you’ve probably noticed already that you might not expect to find at all in a spider: a long, segmented, whip-like tail that resembles the telson found in scorpions.
