- You may be looking for the Delphinus.
A number of Dolphins inhabit the undersea city of Meropis in the Great Blue Realm, where some-including Echo-are members of the Meropis City Guard. As such, they confronted the "intruding" Knothole Freedom Fighters, and became involved in a battle with Dark Gaia's Minions when they invaded the city. (StH: #260, #261, #262, #263)
The Mobini Dolphins of the Sol Zone are extremely helpful to travelers, helping individuals who have been stranded at sea. A group of them came to the aid of Team Rose-minus Blaze the Cat but with the addition of Marine the Raccoon-after the Ocean Tornado was destroyed by the Metal Marauder, and helped them travel to Pirate Island. (SU: #56)