Pic brah. Also probably not. There are 100 million things that can crawl off of live rock and 98% of them are interesting and harmless. Things are still crawling out of my rock 1 year on that I never saw before. Pics would be great (even phone pics). Otherwise, try googling "live rock hitchhikers" and see if your bugger comes up there. Most common that I can think of are sphagetti worms (long strings) or bristleworms (spikey) and both are fine. Bristleworms can give you a little sting so dont touch them, but they are a normal part of the cleanup crew IMO.