Im new here and need help. I have a 14 gallon biocube. For several months I have noticed some small worms in my tank living in my live rock. At first I thought they were baby feather dusters because they appeared a few weeks after my feather dusters died. But now Im not sure. They dont have the plumes and I have notice alot of debris around the base of the rocks. They only come out when the lights are off and when I turn the light on they hide inside the rocks. They are about 4-6 inches long, about 1/8 inch in diameter, smooth and grey in color. If anyone can give me a suggestion as to what they are please help me.