Tonga Nassarrius tails

[KBennett]

Anyone know what the leaf shaped thing on their tails is for?  It glows orange under actinics....

You can see it in this pic:

 

[chrisstevens]

I think that's what blocks the opening on the shell when the snail is all the way inside.

 

[KBennett]

I can't believe I didn't think of that... I wonder why it is jagged and phosphorescent?