This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Oceanid (Greek)
The Oceanids were the 3,000 daughters of Oceanus, the Titan god of the earth encircling river, and his wife, the Titanide Tethys. This parentage made the Oceanids sisters to the 3,000 Potamoi, the river gods of Greek mythology. The 3,000 Oceanids were probably not all born at the same time, and as such some, assumed to be the eldest, are named as Titanide, female second generation Titans.
In the ancient sources the Oceanids would be split into five different groups; the Nephelai were cloud nymphs; the Naiades were the Oceanids associated with fountains springs and wells; the Leimonides were nymphs of the pasture; the Aurai were nymphs of the water found in breezes; and the Anthousai were the Oceanid nymphs of flowers.