All starfish can regenerate limbs if they lose one. If a limb gets broken and part of the central disc is attached to the limb you will actually get a second starfish. This is why in austrailia they were having a problem with the crown of thorns eating the coral reef. So the divers went down...
I think it is this:
COLUMNARIS
SYMPTOMS: White cotton sprouting from fins or body..
TREATMENT: This is a bacterial disease. It can be treated with Fungus Guard or Fungus Eliminator or with MarOxy. It can be spread to other fish and other aquariums by using the same net.
My one molly is sick for sure. I isolated him yesterday. I am pretty sure he has a fungus. He kind of looks dusty. His fins are a little tattered too. The rest of the fish in the tank look good. The only other fish that looks bad is the other one I bought just like the sick one. The...