I have a 55 gallon aquarium about 4 weeks old and the last several days I've seen this thing coming out of my sand. It has been in the same place. It's translucent white and as thick as a couple hair strands...no feathery stuff, just a smooth looking "tentacle." It comes out and "searches"....I've seen it at least an inch, maybe 1.5 inches long. Any idea what it is?