any of a genus (Volvox, family Volvocaceae) of multicellular, free-swimming, flagellated green algae whose cells form a pale green globular colony that rolls about in the water
See volvox in American Heritage Dictionary 4
(vŏlˈvŏksˌ, vôlˈ-)
noun
Any of various freshwater green algae of the genus Volvox that form hollow spherical multicellular colonies.