What were the names of the two sea monsters guarding the Strait of Messina?

In ancient mythology the Strait of Messina between Sicily and mainland Italy was the home of Scylla and Charybdis, two fearsome monsters of the kind the Greeks loved to come up with – both were female, had previously been renowned beauties, who were turned into scabrous horrors only after setting off the jealousy of goddesses, to spend the rest of their days venting their rage on any sailors who dared to make their way through the Strait.