I'm not sure what this little creature is. It is next to a ricordia that is now about the size of a quarter with the lights off, so you get an idea of size. The thing is in the squares in the attached photos. It seems to have a curly tube exoskeleton? And it seems to have a lid that goes up and down and a little creature that kind of looks like snail antennas comes out from time to time. Though this is the most I've seen it come out. And it usually has a tread coming from it too. Sorry for the weird, very non-technical description!