What in the heck

[Canadbis]

So I am looking at my tank about 1/2 hour before the lights turn off and I see this "pocket of diatoms" and I figure I will give them a blast to get them out of the hole in the rock, so I grab my baster and blast some water at them. Well the "diatoms" retreat farther into the hole!!! So I begin to look at this thing and I cant tell quite what it is. It seems to have 5? legs that I can see. One being larger than the others. Then the lights go out! NNNOOOOO
SO I come down stairs and grab the flashlight and go back up. bet you can guess what happens next...The damn thing is gone! I searched hi and low and cant find the thing anywhere.
my description I guess would be, about double the size of a computer screw(case screw), brownish/grey, hairy and thats all I can tell you.
any Ideas??....Anyone?