This is the opening of a mollusk's lung. Here are some sentences.
If you look closely at a slug, you can see its spiracle opening and closing as it breathes.
The snail's spiracle widened.
We studied mollusks in class, and learned about the spiracle.
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A spiracle is a hole that is found on certain animals that helps
them breathe. It is connected to an animalâ??s respiratory system,
similar to a whaleâ??s blowhole.
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The sides of the abdomen.
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spiracle
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The respiratory system of a butterfly is open, and air enters
their bodies via a small opening called a spiracle.