volvox
Concise Oxford English Dictionary © 2008 Oxford University Press:
volvox /ˈvɒlvɒks/
▶noun Biology a green single-celled aquatic organism which forms minute free-swimming spherical colonies. [Genus Volvox.]
– origin mod. L., from L. volvere ‘to roll’.
'volvox' also found in these Oxford entries:

