Here's the Encyclopedia Mythica writeup:
The queen of the sea, variously given as the daughter of Oceanus and Tethys or of Nereus and Doris. When the sea god Poseidon wanted her as his bride, she declined the honor and hid from him in the Atlantic Ocean. A dolphin not only located her, but also brought her back to him, and he married her. The dolphin was awarded a place in heaven. Their son is the fish-man Triton. Amphitrite was portrayed on Greek mphoras together with her consort, riding in a chariot pulled by sea creatures, or sitting on a sea creature, surrounded by Tritons. She is decorated with the attributes of a queen, her waving hair covered with a net, and sometimes with the pincers of a lobster attached to her temples.
The Romans referred to her as Salacia.
The name means something like "The third one who encircles (the sea).
In the "Seven Adventures of Cadida," Amphitrite shows up in "Cadida and the Sea Beast - In Over Her Head," when Dolph, the merhunk, must battle with his wicked uncle, Terrapin, in a dual to the death. Of course, Amphitrite wants her son to win, but she's not so big on the the obvious fact that Dolph is falling for Cadida. Amphitrite appears with a high-pitched voice (dolphin squeaks) and has a crown of crab claws.
This story shows Cadida helping out the merboy, Dolph, find his true meaning. Nasty old uncle, Terrapin, got a witch to toss Dolph out of the sea. He doesn't remember his background, but Cadida, Bascoda, and Poltrice (the pool demon) help him recover his memories and win his true place as Prince of the Sea.