Not an animal, but many marine algae descend from freshwater algae, possibly because the last Snowball Earth event may have wiped out the marine algae by covering the oceans with ice (while freshwater algae survived in structures like cryoconites, tiny freshwater puddles that form on glaciers).

https://www.youtube.com/watch?v=D0R3FVTLvT0

(People who know their taxonomy will notice that I'm conflating algae and cyanobacteria, mea culpa.)