Just thought I'd ask the question, but has anyone ever put anything foreign onto a decorator crab? Something not of nature, to see if it might stick? I'm only asking this question because, SOMEHOW a beer bottle cap found it's way into my fish tank in a position which I can't get it out without...

Have growth coming from live rock not sure what it is.Can any one please ID

Tank specs: 55 gallon (long) FOWLR 70 lbs of live rock 1200 trickle filter coral life protein skimmer 3 fish- 1 clown fish, 1 yellow tail damsel, 1 lawnmower blenny. 1 invert- emerald crab I've had these things at the bottom of my tank in the sand that are green, fat, and long, a lot like if...