The term 'Aquatic Critter' can be summed up by the crossword solution of 'Otter'. Otters are semi-aquatic mammals that live in both freshwater and saltwater habitats. They are members of the Mustelidae family, which includes weasels, badgers, and wolverines. Otters have long, slim bodies with short legs and webbed feet, making them excellent swimmers. They are also known for their playful behavior and intelligence.