Black Lumps on Astrea Snails

[Dos Ocho]

I have 12 Astrea Snails and most have these black lumps on their shells. Never thought much of it, but the one in this pic has been getting bigger and I see a thin white tentacle-like thing coming out the top. Do not see them on rock, walls, or sand. Any ideas as to what these are?

 

[ginpang]

Barnacle maybe?


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[sam.basye]

Looks like a Vermetid snail (reddish/brown tube worm)

I would break them off and toss if it was my tank. They're a nuisance when they release a long white string to catch particulates, especially if you have a lot of them.