Pulmonata (Lung-Bearing Snails and Slugs)

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Pulmonata

(Lung-bearing snails and slugs)

Phylum Mollusca

Class Gastropoda

Subclass Pulmonata

Number of families Approximately 120

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Mainly terrestrial but also freshwater and marine slugs and snails, almost all having an enclosed lung

Evolution and systematics

The earliest fossil pulmonate land snails date back over 300 million years to the Carboniferous period of North America and Europe, although there is some controversy as to whether these belong to primitive pulmonate families such as the Ellobiidae, or to more advanced families of the major terrestrial pulmonate group Stylommatophora. The first certain stylommatophoran fossils date from the Lower Cretaceous (about 140 million years ago [mya]), and become more common during the Upper Cretaceous, with several genera attributable to modern families such as the Plectopylidae, Streptaxidae, and Camaenidae present. Most extant families appear in the fossil record for the first time during the Cenozoic era (from 65 mya).

The subclass Pulmonata evolved from opisthobranch (marine gastropod mollusks of the subclass Opisthobranchia) ancestors, although it is uncertain to which opisthobranch group they are most closely related. The pulmonates include a number of marine and freshwater families within several orders, but are predominantly terrestrial. By far the largest group of land pulmonates is the order Stylommatophora, but there are also several primitive families of slugs (Veronicellidae, Rathousiidae, and Onchidiidae) and snails (Ellobiidae), which are wholly or partly terrestrial. This entire group, excluding the ellobiids, is sometimes united as the Geophila, but it unclear whether it is monophyletic. Molecular studies show that the Stylommatophora are monophyletic, and may have evolved from a terrestrial ellobiid ancestor.

Classification within the Stylommatophora has traditionally been based on the morphology of the pallial system (which includes the lung, kidney, and ureter). Four primary groups, or suborders, were recognized: the Orthurethra, which were thought to be the most primitive, and from which the other three evolved; the Sigmurethra, which includes most of the stylommatophoran families; the Mesurethra, which is a small group with a reduced ureter; and the Heterurethra, which contains only the amphibious family Succineidae.

However, a recent molecular study by Wade, Mordan, and Clarke (2001) shows a very different pattern of phylogenetic relationships within the Stylommatophora. It suggests that there is a primary dichotomy between a smaller, "achatinoid" clade, which includes the "sigmurethran" families Achatinidae, Subulinidae, Freussaciidae and Streptaxidae, and a larger "nonachatinoid" clade, comprising all the remaining sigmurethran families, plus the Orthurethra, Heterurethra, and Mesurethra. The Orthurethra are shown to be a relatively advanced group equivalent to other large superfamilies. The

succineids (Heterurethra) are the sister group of a family of tropical slugs, the Athoracophoridae (together called the Elasmognatha), and are also included within this larger "nonachatinoid" clade, as are the various families which comprised the Mesurethra. The various families of both slugs and predatory pulmonates are shown to have evolved independently numerous times.

There is no general agreement on the classification of terrestrial pulmonates, but that of Vaught (1989) represents a good recent compromise. Vaught's Stylommatophora contains 81 families arranged in 26 superfamilies. There are probably around 25,000 species worldwide. Additionally there are four families of "primitive" pulmonates with terrestrial representatives, which have relatively few species.

The four orders of Pulmonata, based on Burch 1982 and Jeffrey 2001, are the Stylommatophora (terrestrial snails and slugs), Basommatophora (mostly freshwater, also some terrestrial and marine snails and slugs); Systellommatophora (sluglike); and Actophila (marine, intertidal, and brackish-water snails).

The order Basommatophora (15 families, 50 or more genera, and at least 4,000 species) contains a number of relatively primitive families. The order as a whole inhabits a wide range of habitats. The majority of species are freshwater, but there are some terrestrial and intertidal marine families. Some of the better-known families include the Lymnaeidae, dextrally coiled pond snails, some of them amphibious, and some having limpetlike forms.

Members of the family Physidae, sinistrally coiled pond snails, commonly called tadpole snails or pouch snails, are widespread and can tolerate some pollution of their waters. The family Planorbidae, the wheel snails, orb snails or ramshorn snails, is the largest family, in terms of the number of genera and species, of freshwater pulmonates, and is found on all continents and most islands. Many Physidae species are intermediate hosts of the larvae of parasitic worms.

The order Systellommatophora (five families, 11 genera, 50 or more species) comprises sluglike animals with the anus located at the posterior end of the body, in contrast to the normal state of affairs for gastropods in having the anus close to the front of the body. Species of the family Onchidiidae have a posterior pulmonary sac, and those in the family Veronicellidae have discarded the pulmonate lung altogether and instead respirate through their skin.

The order Actophila (five families, nine or more genera, 25 or more species) comprises snails inhabiting salt marshes and mangrove stands. Most species are tropical. In most species, the inner shell is a single cavity, no longer compartmentalized.

Physical characteristics

The Stylommatophora conform to the typical pulmonate body plan. Their main diagnostic characters are the two pairs of retractile tentacles on the head. The upper, longer pair have eyes at the tips, and are concerned with sight and distant olfaction; the smaller, lower pair sense the immediate substrate and food, and are also used in trail following. Additionally, stylommatophorans have a long pedal gland which lies beneath a membrane on the floor of the visceral cavity, and an excretory system with a well-developed secondary ureter.

The shell encloses most of the body organs and is usually dextral (coiling clockwise), but is sinistral (anticlockwise) in a few groups; in some species both coiling directions are represented. The shell is normally cryptically colored, but may be brightly patterned in arboreal species. Some 16 stylommatophoran families are slugs or semi-slugs, in which the shell has been drastically reduced or even lost entirely. In these groups the lung cavity also is greatly reduced and accessory respiratory structures such as the mantle folds are developed. The male and female systems open together as a single genital pore.

Among the primitive pulmonate groups with terrestrial representatives, the tropical veronicellid and rathousiid slugs have two pairs of tentacles, the upper pair with the eyes at the tips; the veronicellids have no lung. Onchidiid slugs, most of which are littoral, have a single pair of tentacles with eyes at the tips. All three of these families lack any form of shell. Ellobiids are snails possessing a single pair of cephalic tentacles, with eyes at the base. The genital openings of the male and female systems are separate in all four of these families.

The largest snails are the giant African land snails of the family Achatinidae, which have been recorded with a shell height of 8 in (20 cm), whereas the tiny European snail Punctum pygmaeum has an adult shell diameter of around 0.04–0.06 in (1–1.5 mm). The foot of the North American banana slug can reach a length of 10 in (25 cm) when crawling.

Pulmonates within the orders Basommatophora, Systellommatophora, and Actophila have diversified into an impressively wide range of forms, with an extensive and often odd variation of shell shapes and details of lung anatomy. There are species with dextrally and sinistrally coiled shells, planispiral shells, limpetlike forms with rounded or conical shells, and sluglike forms. All but the family Veronicellidae bear a functional lung derived from the mantle. The lung is a hollow space within the mantle cavity, lined with tissue liberally supplied with blood vessels for gas exchange. The lung communicates with the outside via a small passage and opening

called the pneumostome. The lung is rendered active by muscular movements within the mantle that alternately compress and expand the lung cavity. Some aquatic and marine families have evolved secondary gill-like structures within their lungs, while others have evolved gill-like organs on the outer body. Limpetlike forms have evolved from more snail-like ancestors several times within the Basommatophora.

Basommatophora bear a single pair of tentacles, the eyes placed at the bases of the tentacles. This category includes more primitive members of the subclass than the land snails or Stylommatophora. Some breathe air, others take oxygen from the water, and some are amphibious, either using a secondary gill when in the water or coming to the surface periodically to breathe.

Among the nonstylommatophorans, two rather primitive families, the Amphibolidae and the Glacidorbidae, still carry an operculum—a moveable, doorlike, chitinous lid that the animals use to close and protect the open end of the shell.

Distribution

Land pulmonates occur in most parts of the globe, extending from hot deserts to beyond the Arctic Circle. They have found their way to even the most remote oceanic islands of the Atlantic and Indo-Pacific.

The nonstylommatophoran pulmonates have spread themselves geographically about as widely as the Stylommatophora, including freshwater bodies and tropical to temperate intertidal zones, on all major landmasses and many islands.

Habitat

Pulmonates occur in most terrestrial habitats, except for the extreme polar and desert regions, although the highest species diversity is found in the moist tropics. They typically live on or near the ground surface, although some families of slugs spend most of their lives burrowing in the soil, and many snails (and a few slugs) are arboreal.

Pulmonates outside the Stylommatophora inhabit tropical and temperate regions. Basommatophorans are mostly freshwater, living in ponds, lakes, streams, and rivers. Systellommatophorans are terrestrial and intertidal-marine, and Actophila prefer tropical salt marshes and mangrove stands.

Behavior

Other than during mating, there is little communication between land pulmonates. "Trail following" is used by some species in locating a mate, or in the case of mollusk-feeding predators, their prey. There is little evidence of territoriality, but crowding can induce aggressive behavior and cannibalism.

Pulmonates are hermaphrodites, and cross-fertilization resulting from reciprocal and simultaneous copulation is the norm. However, several groups are capable of self-fertilization. Sperm exchange can either be internal or external, and if the former, is often mediated by a spermatophore.

The daily activity pattern of most species can be described as crepuscular, the animals being active at dusk and dawn, with varying degrees of activity during the night. Weather is also an important factor, with moisture, but not heavy rainfall, inducing foraging even during the day. In dry conditions snails estivate, withdrawing into the shell and secreting an epiphragm to cover the shell aperture. Typical estivation sites are well above ground level, attached to shaded rock faces or on the stems of plants. During the winter many hibernate, buried in the soil or leaf litter. Homing behavior is quite well developed in some species.

As a whole, nonstylommatophorans lead slow, solitary existences foraging. A few species are carnivorous. Some freshwater pulmonates can regulate buoyancy—sinking, floating, and rising within the water by regulating the air content of the lung. Some can even navigate upside-down across the air-water surface.

Feeding ecology and diet

Most pulmonates are herbivorous, living on fresh and/or dead plant material. Some species, especially arboreal ones, graze on algal films and have specially modified spadelike radular teeth. Slugs and snails also commonly feed on fungi. Several families of slugs and snails are predators, and are specialized for feeding on, for example, earthworms (testacellid slugs) or other snails (spiraxid snails). Most diurnal activity is concerned with foraging, and is crepuscular or nocturnal.

Many insect groups feed on snails and slugs: carabid beetles eat large numbers of slugs, and the larva of the glowworm Lampyris feeds almost exclusively on snails. Flatworms also attack slugs and snails. Birds may use a stone like an anvil to break open the snail's shell. Mammals, such as badgers, rats, and hedgehogs, amphibians, and some reptiles are also important predators.

The vast majority of nonstylommatophoran pulmonates leisurely graze on living and dead plant material, algalbacterial film on intertidal rocks, and, in some cases, carrion. A few species are carnivorous, among them species of the family Glacidorbidae (Basommatophora), snagging and consuming worms and other small aquatic or marine animal life.

Reproductive biology

Courtship is often elaborate in pulmonates and is known to last up to 36 hours in some slugs. It can involve the partners biting each other with their radulae, and the exchange of calcareous darts that pierce the skin and carry chemicals that stimulate sexual activity.

Most species lay eggs in batches in shallow cavities in the soil. Often these are calcified, either containing granules of calcium carbonate or having a calcareous shell. Most eggs are a just few millimeters in diameter, but the shelled eggs of Strophocheilus can reach a maximum diameter of 2 in (5 cm). The brooding of eggs by some Pacific endodontoid snails in the specially enlarged shell umbilicus is a form of maternal behavior, and some arboreal snails construct brood chambers of leaves in which the eggs are laid.

In representatives of several families, eggs are retained in the uterus until they hatch; true viviparity involving a form of placenta appears to be rare. The number of eggs laid varies enormously. Some species lay just one or two eggs each year, whereas the giant African land snail Achatina can lay several thousand in a lifetime. Incubation time varies with species and temperature, sometimes taking as little as three to four weeks, but extending to well over one year in the slug Testacella.

All species in the orders Basommatophora, Systellommatophora, and Actophila are hermaphroditic. Individuals are capable of fertilizing or being fertilized, but only a few species are able to do so simultaneously, since in all but the exceptions, sperm and unfertilized eggs mature at different times. Most species can self-fertilize. Some species can reproduce parthenogenetically, laying unfertilized eggs that develop into adults. Species in the family Siphonaridae still retain a veliger larva during development.

Conservation status

Over 1,000 species of terrestrial pulmonates are listed by the IUCN, of which almost 200 are listed as Extinct, and a further 116 as Critically Endangered. These are mostly endemic snails in the Pacific Islands, where the main causes of extinction are the destruction of the native forest and the introduction of predators for biological control.

The IUCN also includes about 1,000 freshwater mollusks on the 2002 Red List. Problems besetting nonstylommatophoran pulmonates include habitat destruction and pollution of freshwater bodies and intertidal marine areas.

Significance to humans

Many slugs, and fewer species of snails, are major agricultural pests, attacking crops both above and below ground. They also act as the intermediate hosts of important nematode and fluke parasites of humans and domesticated animals. Helicellid land snails carry the fluke Dicrocoelium dendriticum, which infects cattle, and the giant African land snail harbors the larvae of the nematode Angiostrongylus cantonensis, which can cause meningitis in humans. Several of the larger species of snails are eaten as food.

Basommatophoran species, particularly in the family Physidae, are intermediate hosts for parasitic worms that go on to enter the systems of humans and domesticated animals. Some species are used as food by humans.

Species accounts

List of Species

Glacidorbis hedleyi
New Zealand freshwater limpet
Agate snail
Giant African land snail
Spanish slug
Roman snail
Great gray slug
Rosy wolfsnail
Onchidium verruculatum

No common name

Glacidorbis hedleyi

order

Basommatophora

family

Glacidorbidae

taxonomy

Glacidorbis hedleyi Iredale, 1943, Blue Lake, New South Wales, Australia.

other common names

None known.

physical characteristics

Snails with flat-coiled, nearly symmetrical shells ranging from 0.08–0.11 in (2.0–2.8 mm) diameter.

distribution

Southeastern and southwestern Australia, and Tasmania.

habitat

Lakes, ponds, streams, and rivers, usually in acidic waters.

feeding ecology and diet

A scavenger, feeding on carrion, and a carnivore, snagging and eating small freshwater fauna.

behavior

Individuals spend their days hunting and scavenging in their aquatic habitats.

reproductive biology

Only partly understood. Females lay eggs containing already well-developed embryos.

conservation status

Vulnerable.

significance to humans

None known.

New Zealand freshwater limpet

Latia neritoides

order

Basommatophora

family

Latiidae

taxonomy

Latia neritoides Gray, 1850.

other common names

None known.

physical characteristics

Limpetlike form bearing a black shell with an oval shape, the shell up to 0.4 in (11 mm) long, 0.3 in (8 mm) wide, and 0.1 in (4.5 mm) high. A strong, muscular foot equipped with mucous glands and cilia enables the animal to cling to and move about on rocks and logs in rushing streams.

distribution

North Island, New Zealand.

habitat

Cool, rushing streams and rivers.

feeding ecology and diet

Consumes the surface films of algae and bacteria covering underwater rocks.

behavior

Navigates rushing streams underwater by its powerful, muscular foot, using it as both a suction cup and an organ of motility. If disturbed, individuals release a bioluminescent substance based on the chemical interactions of luciferin and luciferase, as in a majority of bioluminescent animals.

Most likely employs its bioluminescence as a defense. The luminous substance, when released by the animal, forms into tiny, individual globules or droplets that could act as lures, the bright, speeding blobs stimulating a predatory fish into chasing the droplets and not the limpet. Or, the bioluminescence may serve to induce a "startle response" in a predator, halting and confusing it while the limpet crawls to safety.

reproductive biology

Mating takes place all year long but least often in July. Individuals each carry an ovitestis, spermoval duct, and uterus. Individuals often mate in triplets, the middle partner both donating and receiving sperm. A fertilized individual will lay several egg clusters or capsules within a few days after mating. A typical egg capsule is oval, transparent and gelatinous, 0.2 in (5 mm) long and 0.08 in (2 mm) wide, with a tough outer membrane, and holding about 30 eggs. These capsules appear to be able to repel growth of fungi and other pathogens. The eggs hatch in about 30 days. The embryos are able to produce the luminescent substance mix 10 days before hatching. Newly hatched latia feed on the eggshells and capsule before moving on to adult fare. The hatchlings have planispiral shells that soon change to the limpetlike form. Average life span is about three years.

conservation status

Not listed by the IUCN.

significance to humans

Since these limpetlike snails are sensitive to pollutants in running water, they serve as indicators of the health of stream and river systems where they live.

Agate snail

Achatinella mustelina

order

Stylommatophora

family

Achatinellidae

taxonomy

Achatinella mustelina Mighels, 1845, Waianae, Oahu, Hawaii, United States.

other common names

English: Oahu tree snail.

physical characteristics

Medium-sized snail. Shell height up to 1 in (2.5 cm) and width up to 0.5 in (1.2 cm). Shell glossy with light brown or dark brown and cream spiral stripes, and small columellar tooth in shell aperture.

distribution

Restricted to mountains of Waianae Range, Oahu, Hawaii, United States.

habitat

Arboreal.

behavior

Nocturnal, but can become active during day in rain. Sedentary; individuals may never move from single tree or shrub.

feeding ecology and diet

Grazes on algal film found on leaves and branches.

reproductive biology

Grows slowly, reaching full size around seven years and living for up to 10 years. Lays no more than one egg per year.

conservation status

Listed as Critically Endangered by the IUCN. Main threats are from habitat destruction, introduced predatory snail Euglandina rosea, and brown rat. Fewer than 10,000 individuals remain.

significance to humans

Provides valuable source of material for study of evolutionary processes. Early Hawaiians used the colorful shells for barter and ornamentation.

Giant African land snail

Lissachatina fulica

order

Stylommatophora

family

Achatinidae

taxonomy

Achatina fulica Bowdich, 1822, Mauritius.

other common names

French: Achatine.

physical characteristics

Large; shell up to 6 in (15 cm), brown with darker zigzag markings; body dark gray or black.

distribution

Native to East Africa and possibly Madagascar; has been introduced by humans throughout much of tropics.

habitat

Lives near human habitation, in gardens, fields, plantations, and secondary woodland.

behavior

Active at dusk, dawn, at night, or even during daytime when it is raining or overcast. Estivates during extreme drought.

feeding ecology and diet

Voracious herbivore, feeds primarily on living plant material.

reproductive biology

Very high reproductive potential, maturing in as little as five months, and laying several batches of 100–200 eggs at a time.

conservation status

Not listed by the IUCN.

significance to humans

Extremely serious agricultural pest, attacking economically important crops and seedlings.

Spanish slug

Arion lusitanicus

order

Stylommatophora

family

Arionidae

taxonomy

Arion lusitanicus Mabille, 1868, Sierra d'Arabida, Portugal.

other common names

German: Spanische wegschnecke.

physical characteristics

Large slug up to 5.5 in (14 cm) long with strong tubercles on body, brick red to dark brown in color, with distinct foot fringe. Lacks dorsal keel on tail.

distribution

Eastern and central Europe, northward to southern England and Scandinavia. Recently range has extended rapidly.

habitat

Tends to live near sites of human activity.

behavior

Daily activity periods typically around dusk and dawn, but strongly influenced by weather.

feeding ecology and diet

Feeds around dusk and dawn; mainly on herbaceous plants, with preference for cultivated plants.

reproductive biology

Produces single brood each year, with hatchlings found in late autumn and early spring, and adults from early summer onward.

conservation status

Not listed by the IUCN.

significance to humans

Serious agricultural pest throughout much of range.

Roman snail

Helix pomatia

order

Stylommatophora

family

Helicidae

taxonomy

Helix pomatia Linnaeus, 1758, France.

other common names

French: Escargot de Bourgogne; German: Weinbergschnecke; Spanish: Cargol de Borgonya.

physical characteristics

Largest European snail, with a globular shell reaching a diameter of 2 in (5 cm), color creamy white with pale brown spiral bands. Body gray with paler tubercles.

distribution

Widespread in Central and Southeast Europe; introduced into United Kingdom, Scandinavia, and Spain.

habitat

Woods, hedges, and herbs, in calcium-rich areas. Extends up to 6,500 ft (2,000 m) in the Alps.

feeding ecology and diet

Herbivorous, feeds principally on living vegetation.

behavior

Hibernates during winter, digging shallow hole and forming chalky epiphragm over shell aperture. Shows strong homing ability over 150–300 ft (50–100 m).

reproductive biology

Courtship elaborate, taking several hours and involving exchange of love darts. Batches of about 40 eggs laid in ground from late spring to summer, hatching three to five weeks later. Matures in three to four years and can live up to 10 years.

conservation status

Not listed by the IUCN, but protected under the terms of the Bern Convention on the conservation of European wildlife and natural habitats.

significance to humans

Prized as food, especially in France, and was farmed by the Romans. A vineyard pest.

Great gray slug

Limax maximus

order

Stylommatophora

family

Limacidae

taxonomy

Limax maximus Linnaeus, 1758, Sweden.

other common names

German: Tigerschnegel.

physical characteristics

Large slug, reaching 8 in (20 cm) extended length. Pale brown or gray, with darker longitudinal bands on side and spotting on mantle. Short keel on back of tail.

distribution

Southern and western European species, extending into southern Scandinavia; introduced into the United States, South Africa, New Zealand, and Australia.

habitat

Common in woods, hedges, and gardens.

feeding ecology and diet

Herbivorous, feeds on fresh leaves and fungi.

behavior

Crepuscular in habit.

reproductive biology

Courtship elaborate, involving circling for up to one hour. Slugs then ascend a vertical surface, then hang entwined, suspended from mucus thread. They evert the penes, which hang down, and exchange sperm masses using special claspers at tips. Penes are then withdrawn, carrying partner's sperm mass. Eggs laid in soil.

conservation status

Not listed by the IUCN.

significance to humans

Occasional pest of ornamental and food plants, especially fruit.

Rosy wolfsnail

Euglandina rosea

order

Stylommatophora

family

Spiraxidae

taxonomy

Euglandina rosea Férussac, 1821, Florida.

other common names

German: Rosige wolfsschnecke.

physical characteristics

Up to 3 in (8 cm) in length. Body long and slender; mouth with hornlike sensory "lips." Glossy, rose-colored, translucent shell.

distribution

Native to the Southeastern United States, from North Carolina to Louisiana; introduced into numerous islands in Indo-Pacific, as well as to Bermuda, Japan, and China.

habitat

Cosmopolitan, lives in wide variety of habitats.

feeding ecology and diet

Voracious carnivore, preys on other snails and slugs.

behavior

Follows slime trails of prey, which it senses with special "lips."

reproductive biology

Lays 25–40 eggs per year.

conservation status

Not threatened, but its introduction onto Pacific Islands in an attempt to control the giant African land snail represents probably the most serious threat to native snail fauna. Has caused the extinction of numerous species of tree snails, such as Achatinella on Hawaii, and Partula on Society Islands.

significance to humans

Used unsuccessfully as control agent against introduced snails of agricultural importance.

No common name

Onchidium verruculatum

order

Systellommatophora

family

Onchiidae

taxonomy

Onchidium verruculatum Cuvier, 1830.

other common names

None known.

physical characteristics

Sluglike marine mollusks with no trace of a shell, ranging in size from 0.4–3.0 in (10–70 mm) long. The dorsal surface is covered by a tough, leathery mantle with a bumpy, rocky-looking surface. The mantle contains an air-breathing lung for use out of water, and has a pneumostome in the posterior region, near the anus, which is also posteriorly placed. When underwater, the animal relies for respiration on its skin and on gill-like protrusions on its dorsal surface. A most interesting and little-understood feature is an array of light-sensitive papillae on the dorsal surface.

distribution

Intertidal zones of continents and islands surrounding the Indian Ocean.

habitat

Intertidal zones, mud flats, and mangrove stands.

feeding ecology and diet

Forages both in and out of the ocean in its intertidal environment, scraping off and eating the films of algae and bacteria that flourish on the surfaces of rocks and mud in this sort of habitat.

behavior

While foraging, an individual leaves a trail of mucus charged with identifying biochemicals, enabling the animal to follow the trail back to its home, usually a sheltered space between rocks.

reproductive biology

When mating, reciprocal fertilization occurs. The fertile eggs are laid in clutches of 60–100, each egg in a tubular capsule, the eggs connected to one another by strands, and the entire egg mass enclosed in a jellylike blob. The parents attach an egg mass to the rocky wall within their shelter.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Abbott, R. Tucker. A Compendium of Landshells. Melbourne, FL: American Malacologists, Inc., 1989.

Barker, G. M., ed. The Biology of Terrestrial Mollusks. Oxford, U.K.: CABI Publishing, 2001.

——. Mollusks as Crop Pests. Oxford, U.K.: CABI Publishing, 2002.

Burch, J. B. Freshwater Snails (Mollusca: Gastropoda) of North America. Cincinnati, OH: U.S. Environmental Protection Agency, 1982.

Mead, Albert R. The Giant African Land Snail: A Problem in Economic Malacology. Chicago: University of Chicago Press, 1961.

Fretter, Vera & J. Peake, eds. Pulmonates: Functional Anatomy and Physiology. Vol. 1. London: Academic Press. 1975.

——. Pulmonates: Systematics, Evolution, and Ecology. Vol. 2A. London: Academic Press, 1978.

——. Pulmonates: Economic Malacology. Vol. 2B. London: Academic Press, 1979.

Solem, Alan. The Shell Makers. New York: John Wiley and Sons, 1974.

South, A. Terrestrial Slugs: Biology, Ecology, and Control. London: Chapman and Hall, 1992.

Vaught, Kay Cunningham. A Classification of the Living Mollusca. Melbourne, FL: American Malacologists Inc., 1989.

Periodicals

Meyer-Rochow V. B., and S. Moore. "Biology of Latia neritoides Gray 1850 (Gastropoda, Pulmonata, Basommatophora): The Only Light-producing Freshwater Snail in the World." Internationale Revue der gesamten Hydrobiologie. 73, no. 1 (1988): 21–43.

Ponder, W. F. "Glacidorbidae (Glacidorbidacea: Basommatophora), New Family and Superfamily of Operculate Freshwater Gastropods." Zoological Journal of the Linnean Society, London 87 (1986): 53–83.

Wade, Christopher M., Peter B. Mordan, and Bryan Clarke. "A Phylogeny of the Land Snails (Gastropoda: Pulmonata)." Proceedings of the Royal Society, Series B 268 (2001): 413–422.