Dive Dry with Dr. Bill

#566: The Chestnut Cowrie

One critter that generally stays out of sight on my day dives, but is frequently seen under cover of darkness is the chestnut cowrie. When I first arrived on Catalina, it was known as Cypraea spadicea, and many still refer to it by that name. However, at some point another marine biologist decided it really should be called Neobernaya spadicea (which almost sounds Russian to me, but I'll have to ask an expert). You can often tell the age of a marine biologist by the scientific name he or she uses for a given species... and I want to appear as young as I can, so I'll adopt the newer name as well.

This species of snail is often praised by collectors for the beauty of its protective armor, a cream colored shell with a large patch of chestnut brown on top ringed by darker brown. However, that's just the shell... when the animal is alive and extends its mantle through the unusual opening on the lower side, the shell is covered by the snail's mantle which is orange in color with black dots. The mantle keeps the shell's surface highly polished by preventing other critters from attaching to it, as is so often the case with the shells of other snails. The shells are 2 to 2 1/2 inches long but some may reach a whopping 4 3/4 inches.

Chestnut cowries are a temperate species, found from Monterey down to Cedros off Baja California, Mexico, but they are not often found north of Pt. Conception. They are said to be more common around our Channel Islands, including Santa Catalina. Preferred habitat is said to be exposed rocky shores from the lower intertidal to subtidal depths. The dive park is located on the island's leeward side, in more protected waters but they are fairly common there. I also used to see them in the eroded nooks and crannies of wooden pier pilings that weren't protected by Chuck Liddell's father's Pileguard wrapping.

The colorful mantle is obvious only when the cowrie is resting and unstressed according to reports. When my video lights strike them at night, the mantle is quickly withdrawn back inside the shell. Another defensive behavior often follows... the cowrie pulls the rest of the body inside as well, and without its foot clinging to the rocks, they fall to the bottom! Good thing they have the thick shells.

I was interested to discover that there is no set age of maturity for this cowrie. Apparently they decide when to become capable of reproduction, probably due to external cues like food or temperature that we scientists don't understand yet. Come to think of it, I've seen a number of humans who don't mature at any set age either... and some never mature!

Cowries were prized by some Native American tribes as a decorative item in jewelry. Apparently even landlubber tribes like those in the Great Plains would trade with coastal tribes to obtain them. Biologist Judith Garfield reported some rather interesting uses for other species of cowrie. In the South Pacific they were attached to the skirts of young women to enhance fertility. I think I'll avoid giving them to any of the lovely mermaids I encounter!

Japanese women apparently held them during childbirth believing they made the delivery easier. In Egypt they were placed in the eye sockets of mummies (but not daddies?). They've even been used by Asian, African and South Pacific cultures as money. Apparently the Chinese found they were harder to counterfeit than coins. Hmmm, maybe I should start collecting them (but not from the dive park of course!). .

Chestnut cowries are carnivores. They feed on "delicacies" ranging from anemones to sponges to tunicates to snail eggs. They will also scavenge on dead critters. I doubt I'll accept an invitation to join them for dinner (or even breakfast).

Here in southern California these snails lay eggs in mid summer, usually July. Approximately 800 individual eggs are laid in pointed capsules attached to the rocks in clusters of about 100. The chestnut cowrie adults are good parents, guarding the eggs for about three weeks until they hatch. At that point, the youngsters enter the plankton as larvae and the parents become empty nesters.

© 2013 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Exposed cowrie shell, two with mantle being withdrawn and the narrow slit on the bottom of the shell they slip into.

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia