SEASHELLS – SNAILS
The one thing anyone visiting the Gulf on Pensacola Beach is going to encounter is a seashell. Many are absolutely beautiful with the colors and shapes controlled by the DNA of the animal that once lived within. The live animal has been eaten by predators or the soft body parts have decayed as the shell made its way to the beach. One of the largest groups of invertebrates in the Gulf are the mollusks, animals that have developed a seashell for protection. The most common shells are snails which are classified as gastropods – one of the few animal groups found in all major habitats: saltwater, freshwater, and land.
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Scotch Bonnet © Stephani Pyron
Snails are different from other mollusks in that they produce a single coiled shell. The shell is made of calcium carbonate (limestone) and is excreted from tissue called the mantle. It covers their body and continues to grow as the snail does. The shell coils around a linear piece of shell called the columella. Most coil to the right, but some to the left – sort of like right and left-handed people. There is an opening in the shell where the snail can extend much of its body. This is called the aperture and some species can close this off with a bony plate when they are inside. Some snail shells have a thin extension near the head that protects the siphon – a tube that acts like a snorkel drawing water in and out of the body.
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Live Mollusk © UF/IFAS – Tyler Jones
Snails have pretty good eyesight and an excellent sense of smell. They possess antenna, which can be tactile (feel) or smell chemicals in the water to provide information to a simple brain. Many gastropods are carnivores, some are herbivores, and others are scavengers. Watch a moon snail prey on a cockle.
Most marine gastropods have separate sexes and exchange male gametes in a sack called a spermatophore. Fertilized eggs are often encased in structures that resemble clusters, or chains of plastic. These are deposited on the seafloor and the young are born with their shell ready for life.
Some of our more common seashells that lived as snails are moons, crown conchs, tulips, slippers, oyster drills, olives, whelks, and augers.
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Moon Snail © Diane Furrow