The American Slipper Shell is so called because when viewed from underneath it resembles a slipper.

The image to the right shows a female slipper shell with a smaller male growing on top of it.

In time, other males could attach on top of the male or the larger female as the "stack" continues to grow.

<click on any image to enlarge>

Slipper shells start life as males and as they mature, become female. 

In time, males could attach on top of the male or the larger female as the "stack" continues to grow.

If a female dies, the largest male in the stack will become female.

In the image to the right, an (improperly) discarded bottle that became home to several slipper shells.

In addition to other male slipper shells, other bay inhabitants such as barnacles and calcareous worms can permanently attach to the shells.

The image below is the top and bottom view of a slipper shell from Barnegat Bay