ocean
A jellyfish drifts through the sea looking soft and simple, but it is missing something important that almost every other animal you know has.
A jellyfish has no brain and no bones at all. Instead of a brain, it has a simple net of nerves spread through its body that senses light and touch and helps it swim gently through the water.
Jellyfish do have tentacles and a sting, so those are things they actually have, not things they lack, which is why they aren't the right answer here.
Jellyfish have drifted through Earth's oceans for hundreds of millions of years, so their soft, brainless bodies were floating around long before dinosaurs ever existed.
ocean
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