Here is a magnified image of a Caecum sp. sea gastropod shell. It was found in 2014 during a diving trip to Key West Florida, USA. The specimen was about 2 km off shore in about 5 meters under the water. I do not think this is a fossil. Viewed under microscope with a 3 mm field of view.
Thanks to Kenny for the specimen and Herb for letting me use his microscope.
Learn more at these sites:
http://shellmuseum.org/shells/shellspic.cfm?sr=21
http://en.wikipedia.org/wiki/Caecum_(gastropod)