Volvox is a polyphyletic genus of multicellular freshwater green algae (Chlorophyta) that belong to a larger taxonomic grouping within the Order Chlamydomonadales known as volvocine algae.
It is free-floating freshwater algae called rolling algae.
The Volvox is called rolling algae because they form tiny structures to form a rolling ball about a height of an inch across.