Baikal sponge (Lubomirskia baicalensis) collected via SCUBA at approximately 10 meters depth in the southern basin of Lake Baikal. The bright green color is due to a symbiotic algae (Zoochlorella) that lives in the external tissue layer of the sponge. This sponge is an important consumer of picoplankton, especially bacteria. A variety of invertebrates including an emerald-green gammarid (Brandtia), oligochaetes, and turbellarians live on or within the tissue of the sponge. The sponge in this photo was collected by staff of the Limnological Institute, Irkutsk, Russia in August, 2001.