Polyphemus (Πολύφημος) was the son of Elatus (or Poseidon) and Hippea. According to one source, he was married to Laonome, sister of Herakles. As a Lapith, he was remembered for having fought against the Kentouri in the days of his youth. Years later, he joined the expedition of the Argonauts. During their stay in Bithynia, Polyphemus was the one to hear Hylas cry as the youth was being dragged away by the nymphs, and when he helped Heralkes search for Hylas. Eventually both were left behind by the Argo for spending so much time looking for Hylas. Eventually Having settled in Mysia, Polyphemus founded the city Kius of which he became king. Later, however, he set out to search for his fellow Argonauts and died in the land of the Khalybes. He was buried at the seashore under a poplar tree.
Either Elatus or Poseidon and Hippea