This thing showed up in my 29 gallon tank. The tank has 30lbs of live sand and about 15lbs of live rock. That is what was left after moving everything to my 125 gallon in the wall. I noticed it last night and tried to scrape it off the rock but it sucked its way inside a hole in the live rock. This morning it was back out. It looked like a black mushroom until I saw it move. I cant really tell, but it has either legs or antennas on its underside. Is this thing good or bad what do I do with it? The last picture shows it has some type of opening at the top, don't know if that is its mouth or what.




