What is "pneumatocyst"

Pneumatocyst \Pneu*mat"o*cyst\, n. [Pneumato- + cyst.] (Zo["o]l.) A cyst or sac of a siphonophore, containing air, and serving as a float, as in Physalia.

n. (context zoology English) A cyst or sac of a siphonophore, containing air and serving as a float.

In phycology, a pneumatocyst is a floating structure that contains gas found on brown seaweed. A seaweed's thallus may have more than one. They provide buoyancy to lift the blades toward the surface, allowing them to receive more sunlight for photosynthesis.

The proportion of gases in the pneumatocysts varies depending on the physiological status of the alga and the partial pressure of gases in the surrounding air or water. The pneumatocyst can hold O, CO, N, and CO.