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How do gas-filled bladders help some brown seaweeds float?
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Algae
The macroscopic genus of algae known as Acetabularia is commonly called “mermaid's wine glass” because of the distinctive umbrella-like shape of the tips of its stalks.
Some brown algae possess gas-filled bladders known as pneumatocysts. These structures function to keep the photosynthetic portions of the algal thallus floating on or near the water's surface, ensuring they remain positioned to receive adequate sunlight for photosynthesis.1