The aquatic park was released on December 11. There are three Classes of Aquatics, Reef, Cave, and Surface. Unlike other groups, there are only two ranks: super rare and legendary. The aquatics are unlocked by beating their events, and once unlocked can be purchased like other creatures. It is possible to obtain Aquatics without beating their event (i,e. Prize Drop and Card Packs) but they will not unlock in this way.
List of Aquatics:
Limited Edition Aquatics
World Event Aquatics:
When these creatures are knocked out they get back up, gaining a level and doubling their stats. Doing damage to them furthers the global progress bar, which gives a reward when filled.
These unreleased aquatics are found by data mining the game.