January 18, 2011 
Snakehead Cowry (Cypraea caputserpentis)
Black-foot 'Opihi (Cellana exarata)
Both of these marine invertebrates are considered marine snails in the phylum Mollusca and class Gastropoda. Most marine snails have spiral shells and are commonly collected for their shells.
Cowries are very unique in that their mantles will expand and cover the entire shell, which keeps the shell nice and shiny! With such a beautiful shell, cowries are commonly collected for jewelry. Scroll down to the bottom of Keoki Stender’s webpage on snakehead cowries to see what one looks like with the mantle covering the shell.
Limpets are also marine snails that are commonly collected by Hawaiians for food. To survive, ‘Opihi graze algae off of rocks and will usually return to the same depression called a “home scar”.
Reef Watch Waikīkī 
Actually, that mantle is also responsible for making the hard shell laying down the color pattern.
I did not know that! Thank you for sharing 🙂