Euphemus was the son of Poseidon and Europe. Euphemus was said to be able to run over water without getting wet (a gift given to him by his father). Euphemus not only was one of the Argonauts who went on the Quest for The Golden Fleece but was one of the Kalydon Hunters who took place in The Hunt For the Kalydon Boar.
Poseidon & Europe
As An Argonaut
After the death of Tiphys, Euphemus became the helmsman of the Argo. This was most likely because of his ability to run over water without getting wet which would give an advance notice as towards the direction the water would be going.