Researchers have found that D-serine, the structural mirror image of L-serine, regulates tissue migration in the marine organism Ciona during its juvenile-to-adult transformation. D-serine binds to NMDAR, leading to the formation and release of a vesicle that assists in tail regression in Ciona. This finding provides the first description of a biological function of a D-amino acid in a non-mammal chordate, elucidating vesicle release mechanisms in organisms other than mammals.