Precuthona are a very small nudibranch variety (less than two in. in length) and live in the shallow waters of the tidal zone to 100 ft deep. <a href='http://science.time.com/2013/01/15/denizens-of-the-deep-alexander-semenovs-pictures-of-undersea-creatures/' target='_blank'>See the complete gallery on TIME.com.</a>