Aquaris is the planet that Larry the Worm is currently the king of.
Initially, Aquaris was just another rock floating through space, albeit a big one. However, with the rising need for a temporary planet that Larry and/or Bob could rule over, Garry, their father, decided that he would terraform the rock, and name the world Aquaris, after the liquid which covered the majority of the planet after the terraforming.
Aquaris is now home to many different species that came from all over the universe to live there. There is, however, no species on Aquaris that is unique to it.