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What is a Gastropod?

O. Wallace
O. Wallace

A gastropod is a single valve (shell), soft-bodied animal belonging to the mollusk phylum. Gastropods, which are also known as univalves or gasteropods, are the largest class belonging to the mollusk family. Estimates of how many species of gastropod are alive today ranges from 65,000 to 90,000. The name gastropod is derived from the Greek words gaster, meaning stomach, and poda, meaning feet. Snails and slugs, both freshwater and saltwater, and other animals that make coiled seashells such as conches, abalones, cowries and limpets belong to the gastropod class.

The gastropod’s most identifiable physical characteristic is its “torsion” process. During its growth and development, the internal organs rotate 180°, so that the anus migrates to just above the gastropod’s head. It has either two or four tentacles, which are used for sensory purposes. While a few gastropods may have more sophisticated eyes, most have simple eyespots at the tip of the tentacles that can discern only light and dark.

Abalone meat. The abalone is a gastropod.
Abalone meat. The abalone is a gastropod.

Another feature that distinguishes a gastropod is its ventral or muscular foot—this foot has a gland that secretes a mucous-like fluid that facilitates easier movement. Although most slugs don’t have the characteristic shell, most gastropods have spiral shells opening on the right side, made out of a horn-like or calcareous material.

Most of us will only come in contact with the typical garden snail or slug, but nearly two-thirds of gastropods live in water, both fresh and salt. Typically, the gastropod is herbivorous, feeding on decaying plant matter, but some are actually carnivorous. Most have a radula, a ribbon-like tongue “system” which cuts and chews the animal’s food before traveling through the esophagus. Burrowing gastropods siphon water to glean food and oxygen through siphoning tubes.

A garden snail is a gastropod.
A garden snail is a gastropod.

Most water dwelling gastropods have gills, but some water and most land species actually have a lung to breathe oxygen. The garden variety snail or slug is typically brown for purposes of camouflage, but some sea slugs are brightly colored, ruffled animals meant to fade into a colorful reef, or warn predators of a nasty sting or poisonous flesh.

With so many different species of gastropod, there is great variance in size. Snails can range from .02 inches (<1 mm) to 30 inches (77 cm). The largest land snail is the Giant African Snail, measuring nearly 16 inches long (39 cm) and weighing two pounds (900 g).

Frequently Asked Questions

What exactly is a gastropod?

A gastropod is a member of the large and diverse class Gastropoda, which includes snails, slugs, and sea slugs. These creatures are characterized by a single, usually spiraled shell and a muscular foot used for locomotion. Gastropods are part of the phylum Mollusca, making them related to bivalves and cephalopods.

How many species of gastropods are there?

There are over 60,000 known species of gastropods, making them the largest class of mollusks. According to the World Register of Marine Species, this number includes both living species and those known only from fossils, showcasing the group's extensive diversity and evolutionary history.

What habitats do gastropods live in?

Gastropods are incredibly versatile and can be found in a wide range of environments. They inhabit marine, freshwater, and terrestrial ecosystems across the globe. From the deepest ocean trenches to the highest mountains, gastropods have adapted to an impressive array of habitats, demonstrating their ecological resilience.

What do gastropods eat?

Gastropods exhibit varied diets, with some being herbivores, others carnivores, and a few omnivores. Herbivorous gastropods typically feed on algae or plant material, while carnivorous ones may consume other mollusks, worms, or even fish. Their feeding strategies are as diverse as their habitats, including grazing, hunting, and scavenging.

How do gastropods reproduce?

Gastropods have a range of reproductive strategies. Many are hermaphrodites, meaning they possess both male and female reproductive organs, which allows for self-fertilization or mating with any other individual. Others have distinct sexes. Some lay eggs, while others give birth to live young, depending on the species and environmental conditions.

Are any gastropod species endangered?

Yes, some gastropod species are endangered due to habitat loss, pollution, over-collection, and the introduction of invasive species. Conservation efforts are in place for various species, such as the IUCN Red List of Threatened Species, which includes gastropods that are at risk of extinction due to human activities and environmental changes.

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    • Abalone meat. The abalone is a gastropod.
      By: kei u
      Abalone meat. The abalone is a gastropod.
    • A garden snail is a gastropod.
      By: JohanSwanepoel
      A garden snail is a gastropod.