Halloween hermit hitch hiker?

[TheBear78]

Evening all,
One of my Halloween hermits has this attached/growing on his shell (the white sectIon on the left end). it looks like some kind of snail shell but hasn't moved from this spot in several days if not weeks. Any ideas? It's unlike any other snail I have in the tank so I'm a bit surprised how it would show up randomly after almost a year!!
Thank you.

 

[ISpeakForTheSeas]

Evening all,
One of my Halloween hermits has this attached/growing on his shell (the white sectIon on the left end). it looks like some kind of snail shell but hasn't moved from this spot in several days if not weeks. Any ideas? It's unlike any other snail I have in the tank so I'm a bit surprised how it would show up randomly after almost a year!!
Thank you.

Given that's it's growing and hasn't moved, I'd guess a sessile, filter feeding snail species of some kind like slipper limpets or hoof snails. Unfortunately, I can't offer a solid ID based off of the photo provided, but if doesn't move, it's almost certainly harmless.

 

[Uncle99]

Maybe pull it off for safety.

 

[vetteguy53081]

Being what looks like its capable of reproduction, I would place crab in small container of tank water and scrape off with a paring knife

 

[sfin52]

Barnicle maybe