Strange shelled invert on Hermit Crab Shell

[Codeman00]

A friend of mine saw this weird invert stuck to my electric blue hermit crab's shell tonight and I wanted to see if you guys could ID it. The white shell is sealed up most of the time but all of a sudden a strange little creature comes out an the opening between its shell and the hermit shell. Hopefully the pictures will help.

If you do ID it, any links to the more info on the little creature is appreciated.

http://reefcentral.com/gallery/data/4008/83895INVERT1a-med.JPG
http://reefcentral.com/gallery/data/4008/83895INVERT2a.JPG
http://reefcentral.com/gallery/data/4008/83895INVERT3a.JPG
http://reefcentral.com/gallery/data/4008/83895INVERT4a.JPG

[capncapo]

Possibly a limpet.

[Codeman00]

I think you're correct...I did a search and found the same creature identified by Dr Ron. Thanks capncapo.

http://reefcentral.com/forums/showthread.php?s=&threadid=715541&highlight=limpet