 The mother of Glaucus was Merope, a daughter of Atlas and one of the Pleiades.By marrying Sisyphus, she became the only one of the Pleiades to mate with a mortal.At first Sisyphus had tried to arrange a marriage for Glaucus with the shape-shifting Mestra, a daughter of Erysichthon, but despite the payment of valuable bride-gifts, she eluded the marriage and was taken to an island by Poseidon.