I have a live rock tank that's been up a little over a year. About 3 weeks ago I came in one evening and saw something new on the front glass. It was about 1/4" to 3/8" in size, appeared to be a star, and had 6 appendages. A day or two later I saw another that appeared to have 3, and maybe more developing. Then a few days later one that had 5 distinct legs. What's up? Are they coming from the rock? Why a year? Why do some have more legs than others?