Creatures that live deep in the ocean (below about 12,000 feet where there's no light at all) look and live entirely differently than their shallow-water cousins.

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The first problem is the pressure. As Mike discovered in Science class, the weight of all that water squeezes them with enormous force. Obviously the creatures have adapted to this pressure. One way they do that is with the same smelly slime that makes fish smell fishy. The more of that slime their bodies contain, the deeper they can live.