The "Star Trek: The Next Generation Technical Manual" lists two Takaya's Whales (Orcinus orca takayai) as being navigators on the Enterprise-D. I looked up the species: it doesn't exist in real life. So I have two theories: first, they could be Orcas from another planet, such as Risa, Pacifica, or some other ocean world (my personal pick is Deneb Kaitos V) or second, they could be an evolutionary offshoot of the orcas we have on Earth today, further evolved into a subspecies that just doesn't exist yet.