What is attached to my Halloween crab??!

[Pristinephoenix]

I need to know what this is. It seems permanently attached to the shell of my Halloween crab. It has a black snout like a snail, and antenna like a snail, but it never moves! It seems to open and shut like some sort of mollusk??! What is it??

 

[Reefing Madness]

Looks like a lil clam

 

[Pristinephoenix]

Clams have a snout?

 

[Reefing Madness]

Kinda like breather tubes, but yea. Its tough to see whats on there exactly, and gets its shape. Im guessing with whta I have here. In the 2nd pic, it looks like a clam.