Embryological and developmental studies confirm that coelom formation takes place during defined stages of embryonic development.
The claim states that coelom formation occurs during specific embryonic developmental stages. Paper [6] details the specific embryonic emergence of the adrenal cortex from the coelomic epithelium, and paper [11] describes the precise embryonic and larval stages during which coelomic structures (like the rostral coelom) form in lancelets. The evidence directly and fully supports the claim.