We don't have synonyms for mesosoma yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are mesosome, mesostoma and metasoma.
(n) :
(zoology) The middle part of the body, or tagma, of arthropods whose body is composed of three parts (the other two being the prosoma and the metasoma), bearing the legs and (in winged insects) the wings.
(n) :
(zoology) The middle part of the body, or tagma, of arthropods whose body is composed of three parts (the other two being the prosoma and the metasoma), bearing the legs and (in winged insects) the wings.