The sea pen, Stylatula, appears to grow up out of the sea floor like a plant but it is actually an animal. The figure on the left shows how it appears under white light, in this case with a brittle star hanging on to it. The figure on the right shows the bioluminescence, which propagates up and down the stalk in waves, much like the lights on a movie marquee. The purpose of these very showy displays is unknown. Image courtesy of Edith Widder/HBOI, NOAA-OE
