THE LADONIDES were the Naiad Nymphs of the Arcadian River Ladon (in southern Greece). They transformed their sister Syrinx into a stand of marsh reeds to escape the god Pan.

Ovid, Metamorphoses 1. 689 ff (trans. Melville) (Roman epic C1st B.C. to C1st A.D.) :
"The Nympha [Syrinx] fled [from the amorous pursuit of Pan] through the wilderness and came at last to Ladon's peaceful sandy stream, and there, her flight barred by the river, begged her Watery Sisters (sorores liquidae) to change her; and, when Pan thought he had captured her, he held instead only the tall marsh reeds."

Sources:

• Ovid, Metamorphoses - Latin Epic C1st BC - C1st AD