A swelling or irregularity in the integument at a joint, as on either side of a chela at the base of the movable finger or between the abdominal somites at the juncture of the terga and the pleura. [Chace and Hobbs, 1969]. Swelling or irregularity in the shell at a joint of an appendage, or between abdominal somites at the juncture of pleuron and tergum [Butler, T.H.].
Crustacea glossary. Natural History Museum of Los Angeles County. 2011.