telson
noun
tel·son ˈtel-sən 
: the terminal segment of the body of an arthropod or segmented worm
especially : that of a crustacean forming the middle lobe of the tail
Example Sentences
Recent Examples on the Web It's also got something that looks like a tail but is actually called a telson — used to flip over the body, which can weigh 10 pounds. 
Carol Motsinger, USA TODAY, 22 Sep. 2020 Uraraneida have more primitive spinnerets and retain the telson that modern day spiders no longer have. John Wenz, Popular Mechanics, 5 Feb. 2018
Carol Motsinger, USA TODAY, 22 Sep. 2020 Uraraneida have more primitive spinnerets and retain the telson that modern day spiders no longer have. John Wenz, Popular Mechanics, 5 Feb. 2018 Word History
Etymology
New Latin, from Greek, end of a plowed field; perhaps akin to Greek telos end
First Known Use
1855, in the meaning defined above
Medical Definition
telson
noun
tel·son ˈtel-sən
: the terminal segment of the body of an arthropod or segmented worm