The difference between naiads and nereids is simple. Naiads are freash water spirits, while Nereids are water spirits of the sea.
Nereids, daughters of Nereus, are the 50 sea nymphs. Some of these include Amphitrite, the wife of Poseidon and Thetis, the mother of Achilles. Other sea nymphs included the Atlantiades, daughters of Atlas, like Calypso, but the Nereids are the traditional "sea nymphs".
Zeus.
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Nereids
I think so.
Sea nymphs.
There is no one named "Nerea" in Greek mythology. The closest would be Nereus, the father of the Nereids.
Both are polytheistic. With gods that are persons.
There are only fifty (50) Nereids, the daughters of Doris and Nereus.
Most ancient authors use the "Third POV".
If you are talking Greek mythology, they are nereids. If you are talking zoology, I hope someone will answer you.
Fresh water nymphs, daughters of the Potamoi (River Gods), granddaughters of the Titans Tethys and Oceanus.