What is this little guy?

i had one in my tank that ate 1 corals and multiple sponges so keep an eye on that one

 

Ok, now I am a little worried....i just saw two more in there! They look cute, but I don't want them to eat my stuff!

 

id take them out the multiply fast my lfs did a test they out 1 of them in a 10g tank and 2 weeks later 20 of them were in thier

 

The ones you watch out for are the dark brown ones. The light colored ones are algae eaters. Yours is harmless, but I would still remove it because they can get out of hand. I had a tank where I was removing 30+ a night. They would all gather in one corner near the top at night for some reason.

The number of legs dont mean anything. They can have up to 8 legs but you rarly see them like that because they reproduce by dropping legs. The one pictured is about to drop a leg and looks like its growing new ones. So its dropped some babies in your tank.

 

I have a bunch of asterina in my tank. They are the mostly white/pale ones and seem to just roam around eating algae. I have heard of them asexually reproducing rapidly, but haven't had a problem in the 2 yrs this tank has been running.

 

I have a lot of the light colored ones. They leave my corals alone, but they do love to munch on coralline algae. Their numbers will fluctuate. They can get out of hand a times, so I just start picking them off the glass with a net to get the numbers down.

 

I have had something of thes ame sort except mine are almost flat and have a tiny opening in the center bottom and slight cone ontop..we are talking minute here, however I have tried to pick them off the rock and they like disinagate <sp?> but leave almost like a sticky slimy bit on the rock that if i try to scrape it off with my finger nail they like get all stringy....any idea??? very hard to take a pic as they are about the size of a pencil eraser even smaller.....only seen a few and I plucked them out as good as I could.....my sun polyps have been slowing disapating when everything else in the tank is thriving....I added a frogspwan 2 weeks ago andI can see a good 1/4+" growth, my xynia is a weed, my green finger leather is very healthy, mushrooms.....so so I have never had luck with shrooms. My pagoda has grown over 2"in 6 weeks, lost a large head of green star polyps abou 3 months ago due to a huge spike in nitrates, that happend after i moved my 50 to a 60 and used some of the old cc substrate but that is ok as I would never replace them...another weed in my book
Just picked up a nice elegance about 5-6" he is on the bottom is doing beautiful.....
So the question is I have heard there is something like I described above that will munch on sun polyps??????any idea from my description??? they are very light tan to almost white?