UPDATE 2011-12-13 07:23
Kylie Karshellian adopted a print of this shell today! See it happen here with annotations and music: http://youtu.be/LtvlLBQnEc0
UPDATE 2011-12-07 21:35
Kendall Karshellian adopted a print of this shell today! See it happen here: http://youtu.be/QpCusZ_q0ww
UPDATE 2011-12-04 19:11
The original oxystele.stl had spiral holes in it. After running it through http://cloud.netfabb.com the holes are gone. If you downloaded the file before, please re-download it.
Another one of M. B. Cortie's greatest hits http://www.sciencedirect.com/science/article/pii/009784939390054D!
Modeled on the shell of the Oxystele sinensis sea snail, http://en.wikipedia.org/wiki/Oxystele_sinensis, will Coenobita clypeatus - "Purple Pincher" - hermit crabs like this? Only experimentation will tell!
It was created using Maya's shellNode plugin, which is based upon Cortie's model, and thickened using Blender's Solidify modifier http://www.blender.org/development/release-logs/blender-256-beta/solidify-modifier/.
The goal is a workflow using open source tools, but this shell surface required a commercial tool. Thanks to a tip from http://www.thingiverse.com/mesheldrake, the conversion to a solid is now handled by an open source tool. :)
Cortie's model and many of its resultant shells have been written in Maple http://www.maplesoft.com/applications/view.aspx?SID=3851&view=html. Porting them to an open source tool such as Sage or Blender is the last step in creating a complete open source workflow.
Any python ninjas up to the task‽
Follow Project Shellter progress here:
http://projectshellter.com
http://twitter.com/ProjectShellter
http://bit.ly/ProjectShellter
http://bit.ly/ProjectShellterCams
http://bit.ly/ProjectShellterVideos

Some notes:

• You must use support material, and it's not as difficult as it sounds! Matt's excellent support settings work great: makerbot.com/blog/2011/06/27/makerbot-microtip-using-the-support-features-in-skeinforges-raft-tool/
  For convenience, they are available here for Skeinforge 35: http://dl.dropbox.com/u/39152244/SF35-Thingomatic-HBP-Mk7-MG-Support.zip
• For printing, you only need the oxystele.stl file; the other file is just a surface and is provided for thickening experiments
• Printing with the aperture facing up and the shell parallel to the printing surface yields the best quality hollow print so far
• Once printed, the minimal support material is easily removed and the entire shell is hollow
• Sanding or tumbling to smooth the surfaces is optional but recommended
  You can print it, I know you can!
  Go!