Hard spikes

[Bclili12]

We took some snails & crabs after a friend had to take his down. All his crabs and snail have hard spikes growing on them, apparently he had quite a bit of these spikes on his rock & power heads too. They are really hard and possibly hollow. Dont seem to grow very big. Havent noticed anything come out, they dont seem barnicle-like. Not sure what it is or if its safe to put in our tank. Any help? Thx in advance.

 

[BelleMorte]

Have those all over the place in my tank and I have noticed fine thread like filiament coming from the getting some of the food I feed the tank and then retracting back into the tube. I have never had an issue with them and my tank is 6 years old