I saw some cowries when I was in Coral Bay. I consulted Snail , who ID them to be the money cowry, Cypraea moneta. Thanks Snail!
I googled the name and found this photo which looks quite similar to mine.
The rocky shore in the south of the Coral Bay jetty - where I found those cowries one evening.
The mantle envelops the shell, getting rid of stuff that lands on the shell and keeping the shell clean. The mantle also deposits enamel onto the shell keeping it polished or glossy.
Inhalant water siphon
Small projections of the mantle which help the animal extracts oxygen from the water
This one almost enveloped its shell completely with its mantle - probably feeling relaxed or sleeping. A cowry will quickly draw its mantle back into the shell when disturbed.