Sarcina is a genus of Gram-positive cocci bacteria in the family Clostridiaceae. A synthesizer of microbial cellulose, various members of the genus are human flora and may be found in the skin and large intestine. The genus's type species is Sarcina ventriculi, a variety found on the surface of cereal seeds, in soil, mud, and in the stomachs of humans, rabbits, and guinea pigs. Magnification: 500x