These beauties are called Stentor coeruleus and are amongst the most admired and popular ciliates around. They measure around 1 mm, which makes it possible to observe them with naked eyes and they possess a blue-green pigment named stentorin. Stentorin plays a major role in light detection and defence mechanisms. When Stentor is being threatened by a predator, the toxin from the stentorin pigment granules are released in the environment, which cause the predator to retreat and gives a chance for S. coeruleus to escape!