noun
- A gas-filled sac or bladder in certain aquatic organisms, such as siphonophores and some seaweeds, that provides buoyancy.
Usage: biology; marine biology
Examples
- The Portuguese man o' war uses its pneumatocyst to stay afloat on the ocean surface.
- Marine biologists studied the pneumatocyst structure of the siphonophore colony.
- The pneumatocyst allows certain jellyfish-like creatures to maintain neutral buoyancy in seawater.
- Damage to the pneumatocyst can cause the organism to sink or lose its position in the water column.