Sea Pansy

A sea pansy, Renilla reniformis, washed up on the sand at Smyrna Dunes Park on Florida's Atlantic coast. It looks like a purple leaf on a stalk, but it is a colony of tiny polyps and a squat kind of sea pen, a group of soft corals in which many species glow. Disturbed in the dark, a sea pansy gives off green light: its luciferase makes the energy and a green fluorescent protein sets the color. Its light-making enzyme, Renilla luciferase, is now a standard tool in biology labs.