First identified in 1899, y-larvae have been one of the greatest zoological mysteries for over a century. No one has ever found an adult of these puzzling crustaceans, despite the plethora of these larvae in plankton, leading generations of marine zoologists to wonder just what y- larvae grow up to be. A study published in BioMed Central’s open access journal, BMC Biology, reports the transformation of the larvae into a previously unseen, wholly un-crustacean-like, parasitic form.