They slip through the water like furry torpedoes, roll on riverbanks like children on a playground and hold hands while they nap. Otters are nature"s playful pranksters. They belong to the Mustelidae family, a diverse group that includes weasels, badgers and minks and are found on every continent except Australia and Antarctica. With 13 species worldwide, including the European otter, giant otter and sea otter—pictured here—these semi-aquatic animals are adapted for life in water. Their webbed feet, dense fur and strong tails make them excellent swimmers. Beyond their cuteness, otters play a vital role in ecosystems.