The term PLAYFUL MARINE MAMMAL can be summarized by two crossword solutions: OTTER (5 letters) and SEAOTTER (8 letters). Otters are semi-aquatic mammals that belong to the Mustelidae family, which also includes weasels, badgers, and wolverines. They are known for their playful behavior and are found in many parts of the world, including Europe, Asia, and North America. Sea otters are a species of otter that live in the coastal waters of the northern and eastern Pacific Ocean. They are the heaviest members of the Mustelidae family and are well-known for their thick fur coats and their ability to use tools.