This ellipsoid shape has low drag through the water allowing the algae to inhabit areas with significant wave and current energy.

Rapid photosynthesis produces a small oxygen bubble inside the sac which holds it toward the surface and the energy of the sun.

[7] The sac tapers to a short stipe, or stem, that connects to a small, disc-shaped holdfast which anchors the algae to the bottom.

[4][9] Older sea sacs sometimes have their tips abraded away, leaving them without their internal supply of water.

The species is found from the Russian Far East to the Bering and Chukchi Seas, the Aleutian Islands, mainland Alaska and south along the coast of North America to Point Conception, California.

The obvious sea sacs that are seen in the intertidal zone are a mix of male gametophytes and asexual tetrasporophytes.

They appear to be identical, but close examination reveals the thalli of the tetrasporophytes to be dotted with the red tetraspores.