Semiaquatic mammal (5)
(Other definitions for otter that I've seen before include "Water mammal" , "furry animal" , "Carnivorous aquatic mammal" , "Freshwater carnivorous mammal with webbed and clawed feet" , "eg Tarka" .)
(Other definitions for hippo that I've seen before include "Augustine looked after" , "Beastly sort" , "Massive thick-skinned animal of African rivers" , "Augustine's place" , "One thick-skinned" .)