The University of California-Santa Barbara researchers said they are the first scientists to look at light-receptive genes in cnidarians, a class of animals that includes corals, jellyfish and sea anemones that have existed for hundreds of millions of years.

"Not only are we the first to analyze these vision genes (opsins) in these early animals, but because we don't find them in earlier evolving animals like sponges, we can put a date on the evolution of light sensitivity in animals," said graduate student David Plachetzki, first author of the study.

"We now have a time frame for the evolution of animal light sensitivity," said Plachetzki. "We know its precursors existed roughly 600 million years ago,"

Assistant Professor Todd Oakley and Plachetzki detail their findings in the current issue of the online journal PLoS One.