These animals are not protected by law, in part because their behavior is difficult to interpret

We've reached the point that research has made us so sure that vertebrates recognize pain that it's illegal in many countries to needlessly harm these animals.
But what about other types of animals like invertebrates? These animals aren't legally protected, partly because their behaviors are harder to read.
We can make good guesses about some of them, like oysters, worms, and jellyfish. These are examples of animals that either lack a brain or have a very simple one.