Snails

by Crystal Cockman

April 24, 2017

Snails are members of the phylum Mollusca and are in the taxonomic class Gastropoda. Slugs are also included in this class. There are 40,000 snail species, which is the largest group of living mollusks. Gastropods have a muscular foot used for movement. They breathe through either lungs or gills.

Snails have a single spirally coiled shell. Slugs lack a shell. Snails are actually born with their shells, though the shell of a baby snail, often referred to as a protoconch or “earliest shell” is colorless and very soft. Baby snails need to consume a lot of calcium to harden their shells, which starts with them eating the shell of the egg from which they hatched. As the snail grows, the shell grows with it. The snail grows new shell material, which also then hardens. The small center of the spiral of a snail’s shell is the original protoconch.

All land snails and slugs are hermaphrodites, producing both spermatozoa and ova, which means all individuals have the potential to lay eggs. Some freshwater and marine snails do have separate sexes. Not all land snails spend their entire life on land, some move between land and freshwater or saltwater. Most land snails have lungs and are pulmonates, but some live in moist areas and have gills.

Most snails have thousands of microscopic tooth-like structures on a ribbon-like tongue called a radula, which they use to rip apart food. A lot of snails are herbivorous, but some are omnivores or carnivores. Some snails even eat other snails.

Photo by John Gerwin.

I found one little snail sitting in the top of a pitcher plant near Black Ankle Bog. It is in the family Polygyridae, which are air breathing land snails, and characteristically have a thickened and somewhat reflexed edge at the opening of their shell. A friend of mine snapped a photo of another snail while out in the Uwharrie National Forest’s Badin Recreational Area. That species was Mesodon thyroidus, which is one of our larger species, as well as one of the most common across the state.

I did a study when I was in college in my ecology class looking at freshwater snails in Eno River State Park, and whether they were communal in nature. They did appear to hang together, but it could have also been that they were following a common food source.

I’m certain you’ve heard of the French eating snails, a dish called escargot, but snails are also eaten in a number of other countries, including places such as Nigeria, Italy, Vietnam, southwestern China, and parts of the United States. The process of raising snails for food is called heliciculture. The eggs of some snails are also eaten similar to caviar.

There are 200+ species of native terrestrial gastropods and 30+ introduced species of land snails or slugs in North Carolina. Approximately 52 species of freshwater snail are found in North Carolina. 74% of all freshwater snails in the United States and Canada are currently imperiled. Conservation efforts for snails have lagged behind conservation efforts for other freshwater species. There is a big need for a better understanding of what taxa exist and what their distribution is. Only by understanding more about snails and how they make their living, can we hope to conserve them.