Plicate Labyrinth Snail

Associated Smithsonian Expert: Robert Hershler, Ph.D.

Dr. Robert Hershler collects tiny amphibious snails at Grapevine Springs, northern Death Valley.

Photo Credit: Hsiu-Ping Liu

Dr. Robert Hershler is a research zoologist and curator of mollusks in the Department of Invertebrate Zoology at the Smithsonian National Museum of Natural History. His current research focuses on systematics, morphology, and biogeography of tiny freshwater gastropods of the superfamily Rissooidea, particularly the western North American fauna. He first became interested in mollusks as an undergrad at SUNY at Stony Brook, where he took classes in invertebrate zoology and assisted in the laboratory of marine biologist Jeffrey Levinton. He majored in biology at Stony Brook and then went on to obtain master's and doctorate degrees in ecology and evolution at Johns Hopkins University.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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Murex snail (Murex sp.) showing operculum
Courtesy of Jan Delsing, via, public domain

About Snails and Slugs (Class Gastropoda ): Body Plan

The gastropods are the most diverse group of mollusks, and include snails, slugs, limpets, conchs, sea slugs, and others. They typically have a coiled body form with a twisted gut and nervous system. The coiling results in the unusual arrangement of their anus being above their head. Most have a corresponding coiled shell. Coils are added as the gastropod grows, and they tend to get larger, making a cone shape. Some shells are adorned with spines, grooves, or other textures that add strength. Many have a hard flap (operculum) on the foot that can be closed over the shell opening like a trap door. The shape of a gastropod shell often can be used to identify species. A gastropod's shell not only protects it from predation, but also keeps land species (terrestrial) from drying out. Some terrestrial gastropods that live in humid places, such as slugs, have a thin shell or no shell at all.

Common Pelican's Foot (Aporrhais pespelecani)
Courtesy of Isidro Martinez, via Flickr: EOL Images, CC-BY-NC-SA

About Mollusks (Phylum Mollusca): Body Plan

Mollusks have soft bodies (mollis = soft) with no internal skeleton. They hold their shape by internal water pressure (a hydrostatic skeleton). A muscular skin-like structure called the mantle covers the back of a mollusk, protecting its mass of internal body organs (viscera). Most mollusks also have a hard shell or at least some hard plates over the mantle. Shells are made of a protein matrix holding together crystals of calcium carbonate. Under those layers is a calcium-containing third layer that in some species is shiny mother-of-pearl. This layered structure makes for a strong shell that protects the soft parts from predators and provides a site for muscle attachment. Most mollusks move their bodies slowly using a muscular structure called the foot to creep along, stick to, or burrow into surfaces, although some mollusks (e.g. squid and scallops) swim.

Snail (Indrella ampulla) defecating
Courtesy of Vipin Baliga, via Flickr: EOL Images, CC-BY-NC-SA


About Mollusks (Phylum Mollusca): Feeding

Most mollusks have a "radula", a ribbon made of chitin with rows of teeth (denticles). The radula is always used to feed, but how it is used varies widely. Radulas are specialized to the diets of mollusks, which range from fully carnivorous to entirely herbivorous. The radula may be used to filter, scrape, crush, cut, or stab, depending what food is eaten. Predatory murexes use the radula to drill holes into other mollusks, whereas limpets use it to scrape algae off rocks. The shape of the radula and denticles can be used to figure out what mollusk it came from. Nudibranchs that feed on corals have long, skinny denticles for scraping the thin layer of flesh off the coral skeleton. Queen conchs have a comb-like radula with thousands of tiny denticles for filtering small food from the water. Regardless, as denticles wear away, they are continuously replaced from top to bottom.

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