Chestnut cowries (Ed Bierman / CC BY)

Egg-like shells are characteristic for this group of sea snails. The smooth and shiny shells have been used as currency by African indigenous people for centuries. The Atlantic deer cowry (Macrocypraea cervus) reaches 19 centimeters (7.5 inches) in length. However, most species are much smaller.

More images » More info »

This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.