Donald Quintana photographed this otherworldly sea creature in a tide pool in Cayucos, California. It's called an opalescent nudibranch, a type of mullusk that sheds its shell after its larval stage.
Do you want your photo of the great outdoors featured on TreeHugger? Join the TreeHugger Photo Pool on Flickr and add your photos to the group!
Update: If you want to see videos of this beautiful creature, here they are: 4 videos of the beautifully strange opalescent nudibranch (aka colorful alien-looking sea slug)