help identify something growing on my nassarius

[Yuva1917]

Can someone tell me what is this growing at the back of my nassarius snails? Its like a tube but can collapse and re appear very fast.

 

[ADAM]

It is likely the operculum you’re referring to that is attached to the top of their foot (tail). They use that to plug the hole in their shell when the retract inside to shield themselves from predators.

 

[Cell]

Interesting, that's not the operculum, but not sure what it is. Are the ridged sides hard or is the entire thing soft?

 

[Yuva1917]

I havent touched it. But it look soft. It retracts and opens quite rapidly. Acting like an anemone? This isnt aiptasia?

 

[Cell]

Not aptasia. This looks nem-like on top but not the sides which looked ridged.

@KJ is good with obscure IDs like this