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Dive Dry with Dr. Bill

#214: Chestnut Cowrie

A few weeks ago I was standing outside Scuba Luv's shop when my old friend Pete Woolsen walked up to say hello. In the course of the conversation, he suggested that I should do a column on what apparently is one of his favorite marine critters, the chestnut cowry (sometimes spelled cowrie). Now when the Assistant City Manager talks, Dr. Bill listens! This one's for you, Pete.

Cowries are a group of snails with a somewhat atypical shell. Instead of having a nice rounded hole with a thick operculum to seal it for protection, cowries often have a long, thin, slit-like opening that may appear to have "teeth" (small molars rather than sharp fangs) known as denticles along the edge. Our only local species, the chestnut cowry, reaches a length of three inches although there are reports of some reaching nearly five inches.

These snails are usually found on rocks from the lower intertidal to depths of 150 feet. Years ago I used to find them on the pier pilings in Avalon and Toyon Bays. However, a good wrap of Orville Liddell's PileGuard may keep them away from the rotting timbers where they used to hide in the crevices. Their geographic range is from Monterey Bay to Cedros Island off Baja California, however they are rare in the colder waters north of Point Conception. The group as a whole favors warmer, often tropical waters (I don't blame them).

The chestnut cowry has a smooth, brown and often very polished shell. This is due to the polishing effect of the soft mantle which often covers it. The edges and underside are white. When the snail inside extends its foot and mantle out of the opening, the fleshy mantle often entirely covers the upper surface of the shell. The color of the mantle is orange-brown with dark spots.

Chestnut cowries may scavenge for food, or they may act as carnivores feeding on sponges, anemones, tunicates and the eggs of other snails. I'm not sure what a snail omelette might taste like, but I must admit I'd lose a lot of weight on a diet like this! However, the cowries seem to thrive on it and are able to grow quite quickly initially, with one reaching a length of 1 1/2 inches within two months. Growth slows significantly as they age.

Little appears to be known about the sex life of a chestnut cowry. Perhaps they are just very modest when housed in a scientist's aquarium. In our region the eggs are laid in capsules during July. Each capsule contains about 800 individual eggs. They lay clusters of 100-120 capsules in one small area. Now we've always been told not to put all our eggs in one basket. In the cowry's case, a predator finding its cluster would have a virtual smorgasbord. However, there is method to their madness. Adult cowries guard their eggs for the roughly three weeks it takes for them to hatch. Grouping them together makes defense much easier.

© 2006 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles" or "Gentle Giants: Giant Sea Bass" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Pair of chestnut cowries, chestnut cowry with mantle extended over shell;
mantle seen from anterior end, slit-like opening on underside of shell.

This document maintained by Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia