Molgula, or sea grapes, are very common, globular, individual marine tunicates roughly the size of grapes.

They are found subtidally, attached to slow-moving submerged objects or organisms.

All species of Molgula have a fluid-filled structure called the renal sac.

[2] The renal sac contains nitrogenous wastes, solid concretions composed of weddellite and calcite,[3] and an apicomplexan symbiont called Nephromyces.

[4] In the western Atlantic Ocean, they range from the Arctic to North Carolina, to the center of the United States Eastern Seaboard.