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The sculpture of this shell of Epitonium scalare is raised vertical ribs which are known as costae. Costae are a common feature in the shells of many species within the genus Epitonium, generally known as wentletraps (a word derived from the Dutch word for spiral staircase). This wentletrap species is particularly large, and the costae are exceptionally well developed; they are in fact the only structure that joins the whorls of the shell together.

This shell was greatly prized in Europe during the 17th and 18th centuries. The shell is still known as the "precious wentletrap", even though it no longer commands high prices from shell collectors.

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The pulmonate land snail Cepaea hortensis crawling up a twig. Because the shell is somewhat translucent in this species, the presence of the pallial lung is noticeable as a relatively large light area showing the volume of air within the mantle cavity.

The muscles that pull back the ommatophores (the two upper tentacles, which have eye spots at the ends) are lightly pigmented, and are visible as two parallel lines that reach through the base of the tentacles and back into the body. Part of the tail protrudes below the shell at the end of the animal. Land snails of this size (shell about 2 cm) can climb vertical surfaces and even hang upside down when necessary.

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A 3D reconstruction of the general anatomy of a preserved specimen of the minute (3 mm) sea slug Pseudunela cornuta, viewed from the right-hand side of the animal. This extremely small, shell-less species of opisthobranch gastropod is found in the Solomon Islands.

In this image, the different internal organ systems of the animal are shown in artificial colors in order to be easier to view and understand. The mass which is colored green near the tip of the animal's visceral hump is the digestive gland. The black dot with the notation "ey" at the head end marks the position of the right eye. "f" marks the foot.

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The snail Indrella ampulla from a tropical rainforest habitat in India. The shell in this species is reduced: the body cannot be fully retracted into the shell. The mantle is partly visible here as an area of off-white color under the edge of the shell. The rest of the body (head with retractile tentacles and most of the foot) is red. The foot fringe is off-white, with narrow black lines. The large caudal mucous pit is visible at the end of the foot.

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The shell of the Venus comb murex Murex pecten has an extremely long siphonal canal. The shell has over one hundred spines, which provide protection from predation, and prevent the snail from sinking in the soft mud. This image shows three views of one shell: an apertural view on the right, abapertural view on the left, and apical view at the bottom.

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A nudibranch Acanthodoris lutea is shown here laying an egg ribbon, in a tide pool in California. Nudibranchs are hermaphrodites, and therefore all adults are capable of laying eggs.

This species is commonly known as the "orange peel doris" because of its striking coloration, which is an example of aposematism. The bright orange color serves as a warning signal to potential predators because this nudibranch is toxic. When it is handled, it gives off a chemical which smells like sandalwood.

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The small air-breathing or pulmonate land snail Cochlicella barbara crawling on a leaf. This species has an unusually high-spired shell compared with others in the same family. The shell is about 7 or 8 mm in length. This species is originally from Europe, but was accidentally introduced to Australia, where it has become a pest on grain crops. This individual was photographed in New South Wales.

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The sea hare Aplysia californica releases a cloud of ink as a defensive mechanism when it is threatened. This species lives in California and the northern part of the Pacific coast of Mexico.

The California sea hare can sometimes grow to be as large as 75 cm in length, measured when actively crawling. It is a herbivore, and feeds mostly on red algae. This species has become a valuable laboratory animal for the study of neurobiology.

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The East African land snail Achatina fulica is a herbivore in the family Achatinidae. This is a very large snail species: its shell length can reach more than 20 cm.

This is one of the most problematic invasive species in the world. It has been accidentally or deliberately introduced to many other areas of the world, where it now represents a very serious threat to agriculture, to native ecosystems, and also to local snails as a food competitor.

The flesh of this species is edible, and in the Western world it is sometimes kept as a pet, but it is under strict quarantine in some countries, (for example the United States), where keeping it as a pet is illegal because of the danger of accidental introduction into the wild.

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Two North American freshwater snails of the species Planorbella trivolvis (synonym: Helisoma trivolvis) in a habitat with floating water weeds, which they prefer. These snails have shells up to 18 mm in width, and are sometimes seen in aquaria.

These snails belong to the family Planorbidae, the ramshorn snails, which are known for their planispiral, left-coiled shells, for having the red blood pigment hemoglobin, and also as intermediate hosts for various parasites, including medically important ones.

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The Spanish slug Arion vulgaris (still often incorrectly referred to as Arion lusitanicus) is a large land slug with a body length of up to 12 cm. It is brown in color. This is a highly invasive species and is considered to be the worst European agricultural pest. It belongs to the family Arionidae, the roundback slugs. Species in this family of slugs have the respiratory opening or pneumostome positioned just anterior to the mid-point of the mantle. The pneumostome is visible in this image as a circular opening behind the head on the right-hand side of the slug. The shell of the Spanish slug is completely reduced, existing only as internal microscopic calcareous granules.

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The California sea hare, Aplysia californica, is a very large marine gastropod which can sometimes reach 75 cm in length. This species has been given priority in sequencing of the whole genome by the National Human Genome Research Institute. It is the first and so far the only marine gastropod which has this level of significance for genetics.

The individual in this image has paused and is rearing up, perhaps to investigate its surroundings. Normally the front part of the foot of the animal is kept on the substrate.

This sea hare has a small and soft internal shell that is made of conchiolin. The two horn-like or ear-like structures on the top of the head (which cause the resting animal to slightly resemble a hare or rabbit) are the rhinophores, which are used primarily for chemoreception.

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This unusual sea slug, the pelagic aeolid nudibranch Glaucus atlanticus, also known as the "sea swallow" has a flattened body with rayed cerata and dark blue stripes along the edge of its foot. This sea slug lives floating upside down at the surface of the water, as shown here from above. Its body is dark and pale blue ventrally (the upper surface as it floats), and silvery grey on its true dorsal side.

This species typically grows to 6 cm in length, and it feeds on medusas, including venomous ones, and also on other pelagic gastropods. Because this sea slug concentrates the stinging power of the medusas, it can deliver a very painful and somewhat dangerous sting to humans.

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An apertural view of a shell of the small, air-breathing, freshwater snail Physella acuta in the family Physidae. This an example of a sinistral or left-handed shell, which means that if the shell is held with the aperture facing the observer, and the spire pointing up, then the aperture is on the left-hand side. In this genus the aperture is long and large, and the spire is pointed. The shell is thin and corneous, and rather transparent.

The family Physidae and the family Planorbidae are within the superfamily Planorboidea; all the species within these families have shells that are left-handed. In general however, sinistral shell coiling is quite rare among the gastropods.

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An apertural view of an adult shell of the extremely large sea snail known as the Australian trumpet, Syrinx aruanus in the family Turbinellidae. This species is the largest Recent shelled gastropod species; the height of the shell can be up to 91 cm.

The shell itself is usually pale apricot in color as shown here, however in life the shell is covered by thick brown or grey periostracum. The whole shell has a spindle-like shape and the spire of the shell is quite high. The whorls usually have a strong keel and the shell has a long siphonal canal. There are no folds on the columella, unlike some other genera within the same family.

In this image, a rod is visible protruding from the siphonal canal; this metal structure is used to support the specimen as it is on display in the Houston Museum of Natural Science.

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A representation of the external and internal anatomy of a common air-breathing land snail such as Helix aspersa. Air-breathing land snails have a well-defined head with two or four sensory tentacles with eyes at the tips of the upper pair, a ventral foot, and a shell. The viscera are grouped in a hump that is contained within the spiral shell.

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This minute Desmoulin's whorl snail Vertigo moulinsiana is an example of a stylommatophoran land snail: it has only one pair of tentacles. Its brown shell has four whorls and is about 3 mm in length.

This rare land snail lives in marshes and swamps in Europe. It is protected by the European Union's Habitats Directive.

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An undescribed species of deepwater nudibranch from Davidson Seamount, Pacific Ocean. Large numbers of species of gastropods have not yet been described and named. Although great efforts have been made, and there has been considerable progress in research on gastropods in the last decade and also in 2010, knowledge on gastropods in general and on the overall diversity of molluscs is still extremely incomplete.

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Four different views of the same shell of the land snail Arianta arbustorum: apertural view (top left) showing its aperture; lateral view (top right); apical view (bottom left) showing its apex and umbilical view (bottom right).

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The video shows the Spanish slug, Arion vulgaris, opening its pneumostome (breathing pore), which is on the right side of its body, in front of the mid-point of the mantle. The pneumostome opens into an internal space that functions as a pallial lung. This space is in fact the mantle cavity of the slug.

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The image shows five different views of one shell of the sea snail species Chicoreus ramosus. This snail is a tropical species that is quite large and predatory.

The shell has a long siphonal canal and shows three varices per whorl. The varices are places where the shell temporarily stopped growing in overall length, and grew in thickness instead, creating in this case elaborate outgrowths as well as a red area on the outer surface of the columella. The shell of this species is in demand as a decorative object, and thus is part of the international shell trade.

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The image shows five different views of one shell of the sea snail species Melo aethiopica, one of the bailer shells. This snail is a tropical species that is very large and predatory.

The shell is almost spherical in overall shape with a very large aperture and a low spire. The shell of this species is in demand as a decorative object, and thus is part of the international shell trade.

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Lambis crocata, the orange spider conch, is a species of large tropical sea snail, a marine gastropod mollusk in the family Strombidae, the true conchs. This is an Indo-Pacific species which lives in shallow water and is frequently found in coral reef areas. The image shows two views of a shell of this species with the anterior end towards the top of the image. The scale bar is 1 cm long.

Like other species within the genus Lambis, the shell of this species has an extended siphonal canal and finger-like processes that protrude from the edge of the shell aperture, which is a bright orange in color. The shell of this species is in demand as a decorative object, and thus is part of the international shell trade.

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Euhadra peliomphala crawling on a tree trunk. This is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Bradybaenidae. This species is endemic to Japan, and exhibits exceptional geographical variation in its mitochondrial DNA.

As Euhadra peliomphala matures sexually, it develops a "head-wart" between the optic tentacles. The development of the "head-wart" parallels the development of the snail's reproductive system. The "head-wart" releases the steroid hormone, testosterone, throughout the body before mating.

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The nudibranch Tambja gabrielae, from the family Polyceridae, has bright yellow spots and stripes on a dark green background. At the head end, towards the left, the two rhinophores are clearly visible, and halfway down the back of the animal its gill rosette can be seen. In this image, all of these structures are being bent back by a strong water current.

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American malacologists at the Washington meeting 1914. Bryant Walker (1856-1936) (back left), George Hubbard Clapp (1858–1949), Truman Heminway Aldrich (1848-1932), John Brooks Henderson Jr. (1870-1923) (back right), Henry Augustus Pilsbry (1862-1957) (front left), William Healey Dall (1845-1927) (front center) and Paul Bartsch (1871-1960) (front right).