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Class Gastropoda - Snails, Sea Slugs, Sea Hares


Festive Nudibranch / aa7ae, Flickr

Festive Nudibranch or Diamondback Nudibranch (Tritonia Festiva)

aa7ae, Flickr
Lightning Whelks / Bob Richmond, Flickr

Lightning Whelks, Busycon sp.

Courtesy Bob Richmond, Flickr
Common periwinkle (Littorina littorea)

Common periwinkle (Littorina littorea)

Blue Ocean Society

The Class Gastropoda includes snails, slugs, limpets and sea hares - all animals referred to as 'gastropods.' Gastropods are mollusks, and a extremely diverse group that includes over 40,000 species. Envision a sea shell, and you're thinking about a gastropod, although this class contains many shell-less animals as well.

Examples of gastropods: whelks, conchs, periwinkles, abalone, limpets, and nudibranchs.


Many gastropods, such as snails and limpets, have one shell. Sea slugs, like nudibranchs and sea hares, do not have a shell, although they may have an internal shell made of protein. Gastropods come in a wide variety of colors, shapes and sizes.

Characteristics of Gastropods:

  • Many gastropods have one shell in which the animal can withdraw. The shell is usually coiled, and may be 'left-handed' or sinistral (spiraled counter-clockwise) or 'right-handed' or dextral (clockwise).
  • Gastropods move using a muscular foot.
  • All young (larval stage) gastropods undergo a process called torsion, in which the entire top of their body twists 180 degrees on their foot. This results in the placement of the gills and anus above the head. Gastropods have adapted in a variety of ways to avoid polluting their breathing water with their own wastes.
  • Due to torsion, adult gastropods are asymmetrical in form.


  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Gastropoda



Such a diverse group of organisms has diverse feeding mechanisms. Some are herbivores, some carnivores. Most feed using a radula. The whelk, a type of gastropod, use their radula to drill a hole into the shell of other organisms for food.

Food is digested in the stomach. Because of the torsion process described earlier, the food enters the stomach through the posterior (back) end, and wastes leave through the anterior (front) end.


Some gastropods have both sexes; some are hermaphroditic. One interesting animal is the slipper shell, which may start out as a male and then change to a female.

Depending on the species, gastropods may reproduce by releasing gametes into the water, or by transferring the male's sperm into the female, who uses it to fertilize her eggs.

Once eggs hatch, the gastropod is usually a planktonic larvae called a veliger, which may feed on plankton or not feed at all. Eventually, the veliger undergoes metamorphosis and forms a juvenile gastropod.

Habitat and Distribution:

Gastropods live just about everywhere on Earth - salt water, fresh water, and on land. In the ocean, they live in both shallow, intertidal areas and the deep sea.

Conservation & Human Uses:

Many gastropods are used by humans for food, decoration (e.g., sea shells) and jewelry.

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