Volvox algal colony. Light microscopy footage of a colony of the freshwater green alga Volvox globator. The colony is a hollow sphere made up from thousands of cells connected by cytoplasmic threads and arranged in a single layer. Each cell has two flagella, which point outwards, and are used for locomotion. The green spheres within the colony are embryos for daughter colonies, which are produced asexually. The diameter of the individual cells is less than 10 micrometres. A colony can grow to more than 1 millimetre in diameter. This colony is not moving freely because it is held in place by a coverslip.