What is the mythical greek pet for Poseidon?

Poseidon, the Greek god of the sea, is famously associated with horses, not pets. He is often depicted riding a chariot drawn by horses, and the hippocampus, a mythical creature with a horse's head and a fish's tail, is considered sacred to him.

While he doesn't have a singular "pet" in the traditional sense, horses and hippocampi represent his power and dominion over the seas.