Arethusa was a wood nymph from Elis, associated with the goddess Artemis. Pursued relentlessly by the river-god Alpheus, Arethusa begged for Artemis’s help in escaping his attentions. The goddess opened up a passage under the sea which enabled Arethusa to emerge as a spring in Syracuse, on the island of Ortygia (Sicily) – hence the seaweed in Yevonde’s sitter’s hair. (quoted from NPG)