Aquatic Adaptations
The water opossum has several adaptations for its watery lifestyle. It has short, dense fur which is water-repellent. The broad hindfeet are webbed and are used for propulsion through water, moving with alternate strokes. They are symmetrical as well, which distributes force equally along both borders of the webbing; this increases the efficiency of the water opossum's movement through the water. The yapok's long tail also aids in swimming.
Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming. A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water. The male also has a pouch (although not as watertight as the female's), where he places his genitalia before swimming. This is thought to prevent it from becoming tangled in aquatic vegetation and is probably helpful in streamlining the animal as well.
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