Atlantis was technically never proven to have existed, only speculations and accounts from Platos 'the Republic'. When you were talking about some sea deity, did you mean like Neptune, Posidon, Triton?
Pendragin, story is not than easy. Platos took that from Lawmaker Solon, his ancestor. Solon took from Egypt.
There are maps in Egyptian sarcophagi with the exact situation of Atlantis, right where Platon said in Timeo and Critias dialogues, beyond the Pillars of Hercules, extending along the coast of southern Spain and North Africa to the west.
In last years a young Cuban-Hispanic historian has been found submerged constructions in southern Spain coasts (or north Africa). He even photographed pieces (in private collections) made by "orichalcum". Orichalcum means mount copper, literally.
But authorities deny any attempt to research, a British team offered his equipment to this young historian for free, but will never obtain the permits. His name is Georgeos Díaz-Montexano
His books:
http://www.amazon.com/Georgeos-D%C3%ADaz-Montexano/e/B009235OXY/
As has been mentioned, we don't know that Atlantis ever existed. Plato wrote about it, not so much as a real place but rather as an philosopical example of a doomed society in "The Repurblic". Plato did not, as far as I can remember, mention any specific deities that were worshiped in Atlantis.
It is now thought that the society that Plato might have been talking about when he mentioned Atlantis was actually the Minoan culture of Crete. The Minoans were a powerful people of the sea with trading ships and colonies all over the Mediterranean. They were largely distroyed when the volcano, Thera, erupted around 1500 BC. Following the volcanic eruption and subsequent tidal wave they were invaded and conquered by the Mycenaeans (early Greek society).
Many of the Greek gods were actually "borrowed" from the Minoans following the conquest of the Minoan empire. We do know that the Minoans had a God they referred to as "Earth Shaker" and the that image of the bull was very important to them. This coincides with the Greek God of the sea, Poseidon, who as also called "Earth Shaker" by the Greeks and ruled over both the sea and over earthquakes. Poseidon is also associated with the bull.
So I guess what I am saying is that if they are right about Atlantis and Minoan Crete being one and the same, then Poseidon would have been the God you are looking for.
Lark, you know a lot .... Can't remember any Atlantis deities, but you're right with EarthShaker, in Odyssey is mentioned several times, but I can't see he like a bull, is more typical of Zeus. Near the Minoans there was another bull deity, Moloch, looks the same to me.
In my humble opinion, because is no more than opinion, Minoan do not fit the descriptions provided by Platos, he said clearly, beyond Pillars of Hercules, a continent, swallowed by the waters ... if we accept that it was not a simple story that Solon took from Egypt. The maps from Egypt are the most favorable clue to this theory, check:
There is also a fascinating theory that Plato was actually writing about the Trojan War. The archeological evidence shows that the harbors and hill site of Troy was much like the descriptions of Atlantis. And the "Gatesof Hercules" could well have been the Straits of the Bosphorus. Hercules did sail with Jason and the Argonauts through the Bosphorus into the Black Sea, but he never ventured out of the Mediterranean through the Straits of Gibralter. Try the book " The Flood from Heaven " by Eberhard Zangger.
Take Plato's writings as an allegory, not as fact.
Troy too? Another one to the list. Each historian takes the one better fits in his beliefs. Anyway would only be bronze or iron age civilization, nothing to do with advanced technology or extraterrestrial beings.
Yes, Platos liked allegories, and is the only one who speaks of Atlantis, Aristotle does not mention in his extensive work, as far as I remember.