Shells-Creatures of the Night

By Al Hornsby

On nighttime reefs, some of nature's most beautiful and least understood animals-shells-prowl in search of food. Shells are mollusks of the gastropod group (they have a univalve shell as opposed to bivalves like clams and oysters). They are also related to other mollusks like nudibranchs, squids and octopus. They grow lovely, colorful external skeletons of calcium carbonate.
Unfortunately, most people know them in their dead state, scattered along beaches or on display in shell shops. Live, however, their secretive habits-most are active at night-and superb camouflage make them difficult to find.
Although shells are found in virtually all fresh and salt water environments, tropical waters have the most dramatic, beautiful varieties. The many species are recognized by the different shapes and patterns of their shells. They occupy quite specific habitats-mud, sand, algae-covered rock, dead coral, live coral-and some stay deep, while others remain shallow. Finding particular shells means knowing where they live and when they are active.
The Caribbean has many striking species, especially conches (Strombus), but in the Indo-Pacific region, shells are especially numerous and diverse. Among the most interesting are the cone shells (Conus), particularly the piscivorous species, which eat fish after paralyzing them with a poisonous sting. Conus geographus, the Geography Cone, shown here in a photograph taken late one night off the island of Cosmoledo in the Indian Ocean, is particularly impressive. Reaching more than five inches long, it can be found crawling across rubble-covered bottom in the dark. It is an active, aggressive hunter that locates prey by smell. When it finds a small sleeping fish, it stings it with a tiny harpoon (its radular tooth) located in its proboscis and injects a powerful poison. (Handle with care-they'll sting you, too). It then feeds by expanding its proboscis and ingesting the fish whole.
Besides the simple thrill of finding a beautiful specimen, these brightly-colored, intricately-patterned slow-as-molasses critters are perfect for photographers: you won't find a more cooperative subject anywhere!