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Chestnut cowrie has polished reputation

The community of La Jolla is often referred to as “the jewel” but there is another jewel that graces the La Jolla Ecological Reserve. The chestnut cowrie (Neobernaya spadicea) is the only true cowrie snail to live in our temperate waters off our coast, most cowrie species being tropical. The striking egg-shaped shell is colored orange, tan, and white but dominated by a rich chestnut brown. The under part of the shell has a long open slit framed by white "teeth" that provide protection from predators.

A unique aspect of a cowrie's shell is its polished look, which is maintained by the animal itself. Two fleshy sides of the mantle (orange skin studded with black dots) emanate from the opening slit and slide up over the shell until they touch. It's not often to see the mantle fully enveloping the shell because the flesh is only fully revealed when the animal is sleeping or not stressed. It only takes one flash of a strobe, and a cowrie's mantle begins to retract. This practice accounts for the exquisite luster of the shell but does not explain the benefit to the animal. In fact, it seems counterintuitive because a shell typically exists to hide most of an animal's soft parts. Here, the hard part still acts to safeguard the flesh but the fleshy part also protects the hard part by preventing potential hitchhikers from forming any attachment. Why this is important to the cowrie and not most other snails is unknown.

One compelling aspect of cowries is that, unlike most animals, they decide when it is time to transform from being a juvenile to an adult. Size has nothing to do with it. Typically, size determines where they are at in terms of sexual maturity. For cowries, even at an early stage of growth, they can infold the shell's outer lip and thicken it overall despite being baby sized. Such cowries and their shells are referred to as dwarf adults. Certainly, there must be outside pressures that influence if and when a cowrie makes the leap to adulthood, such as water temperature and food sources, but the details are unknown.

A cowrie's good looks has its downside because it is irresistible to humans who have, through the ages, many uses for and beliefs about the shells. Certainly, they were ornamental, being particularly popular in necklaces and broaches. North American Plains Indians traded with other tribes to obtain them. Cowries were believed by many cultures to possess special magical properties. In many areas of the South Pacific they were worn on the skirts of young women, believing they ensured fertility. In Japan, cowries were often held during childbirth to help ease delivery. Cowries have also been used to ward off the evil eye and were placed on graves to ensure the afterlife of the deceased. In Egypt, cowries were placed in eye sockets of some mummies. Cowries have been used as money in many civilizations. In China, the shells were used as currency as early as 1000 BCE, as well as in India, Africa, and the South Pacific. The Chinese tried to replace the cowrie with coins as legal tender but returned to cowrie currency because counterfeiters were too skillful at duplicating the coins. Today, cowries continue to be hunted and traded by collectors, likely for the same reasons they have been historically singled out: they are beautiful and need no additional work to make them shine.

— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to