Ocean Watch: Exquisite cowry shells are to be admired

When I realized I was going to fall short of the white seashells I needed in an art piece I’m making, my friend Chris offered two bags of shells that she and her husband, Matt, had collected from Hawaii’s beaches. Among the variety in the bags, I found a pleasant surprise: a hundred or so inch-long brown cowries with brown-and-white spotted domes.

After moving the cowry shells into their own dish, I ran my fingers through the marblelike snail skeletons, struck by so much beauty in a bowl. These were snakehead cowries, one of Hawaii’s most common, and lovely, shallow- water cowry species.

Cowries are marine snails universally loved for their glossy, egg shaped shells. Their unique form comes from the snail’s outer coil wrapping completely around the inner coils, thereby hiding the familiar spirals we often see in other snails.

A cowry’s shiny shell is the result of its fleshy cloak, called a mantle, that extends from both sides of the snail’s toothed, underside slit. The mantle’s two halves creep up and over the shell, meeting in a pale line that runs the length of the cowry.

Although we never see it in dead cowries, the mantle can be as striking as the shell it covers. Cowrie mantles range from bright red to velvet black, with single or bushy knobs tipped in red, pink, purple or white.

The snakehead cowry’s mantle is olive-brown, dotted with yellows and greens. Red bulbs tip its tiny, cone-shaped projections.

In addition to helping a cowry breathe and hide, cowries’ cloaks of many colors provide the brick-and-mortar of the cowry’s shell, secreting calcium carbonate to repair and thicken. Most snails grow their shells from the inside out, which is why their insides are so shiny. Cowries do it outside in.

When a cowry is disturbed, it quickly retracts its mantle, revealing a stunning shell made glossy by the mantle.

The snakehead cowry, found throughout the Indian and Pacific oceans, likely got its name from areas that host snakes. Hawaii’s snakehead cowry is a bit smaller and slightly different in color from those in other areas. Ancient Hawaiians called it leho kupa, meaning small cowry.

Snakeheads hide in cracks and under rocks near the shoreline during the day and graze on algae at night. This is when snail-eating cone snails strike. The predators bury themselves under the sand, and as a snakehead (or other snail) forages along the ocean floor, the cone snail pokes its venomous stinger into the snakehead’s flesh.

When we find perfect, intact snakehead shells on beaches, a good guess is that a cone snail ate the animal inside, and waves washed the empty shell ashore.

I’m with Chris and Matt in admiring Hawaii’s snakehead cowries, and also agree with them that these exquisite snail skeletons should return to the ocean, nature’s grand recycler. We will give them back with the reverence they deserve.

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