i was looking ta my tank last night about 3 hours after lights out and found 2 little brittle stars a little bigger then a nickel on a rock moving around. i have been reading about them and it says they can reproduce by breaking off segments of their body or normal reproduction but i only have one that i know of in the tank and i dont know of it ever being harmed. but i know i have two little guys for sure and possibly seen about 4 more but couldnt get full body shots to tell.
