Ponds and ditches are not only home to unicellular green algae, but also to multicellular forms.
Some ‘colonies’ are nothing more than a mass of single cells all doing exactly the same thing, but with the spherical volvox it’s a slightly different story. Here different cells have specialised and work together. All the cells are located on the outside of the sphere. There are cells with flagella (whip-like hairs) to help the colony move around and cells which are responsible for reproduction.