Noctiluca species are some of the largest single-celled organisms in the world. The most well known of the genus is Noctiluca scintillans, which may grow from 200 to 2000 microns in diameter. These dinoflagellates possess nearly spherical, balloon-like bodies that lack a pronounced girdle. The organisms do, however, retain two flagella, though they are highly modified, not always noticeable, and are not strong enough to readily facilitate locomotion. Rather, Noctiluca scintillans controls its vertical position by regulating its buoyancy, often floating just under the surface of the water.