Volvox (vol-vox) is the iconic colonial volvocid - motile green alga. In this case hundred of cells are embedded in a sphere of common mucus. Each individual cell is tiny, linked to others by fine threads of cytoplasm, has two flagella, and a cup-shaped chloroplast - a bit like a Chlamydomonas cell. There are a number of related genera which form colonies using mucus as a common matrix, but they differ in the numbers of cells involved, how tightly packed they are, and the shape of the colony. This picture is of several colonies, the two lower ones contain a number of smaller daughter colonies within. Differential interference contrast.