Pest on Trochus Snail?

[Jud]

Apologies for the terrible photo - took this after lights out with an iPhone and a flashlight.

One of my Trochus snails has two little protuberances coming from it's shell - one with a long strand coming from it.

They look like coralline, but I've never seen it grow in "spires" from the shell like this.

Any idea if it's harmless or something I should worry about?

 

[AdamNC]

Vermetid snail

Fine in small amounts on the rock but I'd remove it from the Trochus. The webbing it puts out could annoy the snail. Just take a flat metal tool and scrape it off.