I really have no idea since the "ranks" are fitting pretty good imo and the term "whale" is well known around the cryptosphere. Additional to this: I don't really care so much about a "rank" because they do not tell how experienced the user is. It only states how big and full the wallet is and how much impact the user has on the system.
I think that @goldrooster's idea is my favourite so far but as I've said: Today I am dolphin, in 13 weeks a plankton and then a dolphin again.
Perhaps there could be just "top X" ranks. That would be way easier to understand.