Darkfield image of spherical colonies of Nostoc commune, a bluegreen alga. Nostoc commune is a terrestrial species of cyanobacteria that in 1988 was found to harbor a previously unidentified UV-A/B absorbing pigment. This protective pigment has enabled them to survive not only while under hydration-related stress, but in areas of extreme UV radiation as well. Nostoc commune is composed of rubbery sheets when hydrated but appear as a crispy sheet when dry. Tenth Prize, 2011 Olympus BioScapes Digital Imaging Competition®.