Thompsonia is a genus of barnacles which has evolved into an endoparasite of other crustaceans, including crabs and snapping shrimp.

[1] It spreads through the host's body as a network of threads, and produces many egg capsules which emerge through joints in the host's shell.

[2] The first scientific description of the genus was Robby Kossmann's description in 1872 of Thompsonia globosa.

[3][4] Kossmann named the genus after John Vaughan Thompson, the Irish naturalist who had recognised the cirripedian affinities of the Rhizocephala.

[3] The type specimens had been collected by Georg Semper in the East Indies, on the legs of the crab Lybia tessellata.