Rita Santos in Mako Mermaids. He used to be feared greatly by Sirena, Lyla, and Nixie because they were new to land and were unaware what he was, but later find out that he is nothing to fear over and that he accepts them. The cat does later lead the girls to Rita's secret mermaid cave hidden in her office.
Poseidon is an exotic male long hair chinchilla. He is Rita's closest friend and companion, guarding her house and possessions and also his very own secret.
- Poseidon is potrayed by a cat name Monte.
- The cast says that they use a fake cat for some scenes.