Gastropoda Facts

The class Gastropoda includes snails, slugs, limpets, and sea hares; the common name for all of these animals is "gastropods." Gastropods are a subset of mollusks, an extremely diverse group that includes over 40,000 species. A seashell is a gastropod although this class contains many shell-less animals as well.

Description

Examples of gastropods include 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.

Gastropods with one shell use it to hide in. 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. Due to torsion, a behavior in which the gastropod twists the top of its body 180 degrees with respect to its foot as they grow, adult gastropods are asymmetrical in form.

The class of gastropods belongs to the Animalia kingdom and the Mollusca phylum.

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Gastropod Facts

By Jennifer Kennedy

Habitat and Distribution

Gastropods live just about everywhere on Earth—in salt water, fresh water, and on land. In the oceans, they live in both shallow, intertidal areas and the deep sea. On land, they are in wet marshy environments to deserts, from shorelines and beaches to the mountaintops.

The complexity of a given habitat, whether on sea or shore or mountaintop, positively affects the density and richness of the gastropods found within it.

Diet and Behavior

This diverse group of organisms employs a wide range of feeding mechanisms. Some are herbivores and some are carnivores. Most feed using a radula, a bony structure of tiny teeth used for scraping food off a surface. 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, the food enters the stomach through the posterior (back) end, and wastes leave through the anterior (front) end.

Reproduction and Offspring

Some gastropods have both sexual organs, meaning that 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 the eggs hatch, the gastropod is usually 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.

All young (larval stage) gastropods rotate their body as they grow, resulting 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.

Threats

Most gastropods on earth are listed by the International Union for Conservation of Nature (IUCN) as "Least Concerned." However, there are many exceptions, such as the Xerocrassa montserratensis, a terrestrial gastropod that lives in shrublands and mountain peaks in Spain and is listed as endangered by fires and fire suppression and recreational activities. Well over 200 species are listed as extinct by the IUCN; many others, particularly freshwater and terrestrial species, are listed as endangered.

Sources

• Aktipis, S.W. et al. "Gastropoda: an overview and analysis." Phylogeny and Evolution of the Mollusca. Eds. Ponder, W. and D.L. Lindberg. Berkeley: University of California Press, 2008. 201–237.
• Auld, J. R., and P. Jarne. "Sex and Recombination in Snails." Encyclopedia of Evolutionary Biology. Ed. Kliman, Richard M. Oxford: Academic Press, 2016. 49–60. 
• Beck, Michael W. "Separating the Elements of Habitat Structure: Independent Effects of Habitat Complexity and Structural Components on Rocky Intertidal Gastropods." Journal of Experimental Marine Biology and Ecology 249.1 (2000): 29-49.
• Frýda, J. "Fossil Invertebrates: Gastropods." Reference Module in Earth Systems and Environmental Sciences. Elsevier, 2013. 
• Martínez-Ortí, A. Xerocrassa montserratensis. The IUCN Red List of Threatened Species 2011: e.T22254A9368348, 2011.