What a mouthful of a name for this adorably tiny eel-looking critter that is often seen dwelling inside a LPS coral. Siokunichthys nigrolineatus is also known as the Mushroom-coral Pipefish. Typically found in Indonesia, Philippines. They grow to 8 cm in length, but remain very thin. In this picture they are within a Heliofungia coral. There are at least four in this picture.
Photo by Richard Ross
Here's another picture (below) by Diana Schmitt, a SCUBA diver friend of mine.