elementary body

noun

el·​e·​men·​ta·​ry body ˌel-ə-ˌment-ə-rē-, -ˌmen-trē- 

: an infectious particle of any of several microorganisms

especially : a chlamydial cell of an extracellular infectious form that attaches to receptors on the membrane of the host cell and is taken up by endocytosis compare reticulate body