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How did Snails Come to Live on Land?

Part 1: Ecology and Habitats Part 2: Systematics Part 3: Morphology and Development Part 4: Ecology and Protection
  How Did Snails Come to Live on Land?    

Contents

Introduction

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Dimensions in terrestrial pulmonate snails (Stylommatophora):
Point snail (Punctum pygmaeum) compared to Ena montana.		  
Mountain bulin snail (Ena montana) compared to the Roman snail
(Helix pomatia). Pictures: Stefan Haller (schneckenfoto.ch).
Secondary Air Respiration in Land Operculates?

Land operculate snails are descended from gill-bearing gastropods. As a result, they do not possess a true lung. Instead, their mantle cavity has secondarily evolved into a lung-like structure, while the gills have mostly been reduced. There is also no pneumostome (breathing pore); instead, gas exchange takes place through a large opening at the edge of the shell.

This condition is referred to as pseudopulmonate or secondarily pulmonate.

Wikipedia: Respiratory system of gastropods.
Stijn Ghesquiere: Ampullariidae Respiration.		  
Thanks to the evolution of lung-based respiration, the pulmonate snails are by far the most species-rich group of gastropods to have successfully made the transition from the sea to land during their evolutionary history. This adaptation led to an enormous diversity of species, especially within the terrestrial pulmonate snails known as Stylommatophora, which – with an estimated 25,000 to 30,000 species – represent, alongside the Caenogastropoda, one of the two largest groups within the Gastropoda.

If the Hygrophila (formerly: freshwater pulmonates – Basommatophora) are included, roughly 39% of all known snail species belong to the Pulmonata.

However, pulmonates are by no means the only gastropods to have conquered terrestrial habitats over the course of evolution. In fact, a number of other, phylogenetically unrelated groups have independently managed the transition to land. Unlike pulmonates, these are all operculate land snails – that is, they possess an operculum, or shell lid.

For example, the round-mouthed snail (Pomatias elegans) belongs to the Littorinimorpha, and thus to the large group of Caenogastropoda, but not to the pulmonates. The grey turret snail (Cochlostoma henricae), on the other hand, belongs to the Architaenioglossa, another subgroup of the Caenogastropoda – just like the freshwater river snails (Viviparidae). Finally, the tropical Helicinidae, which we have already encountered among the Neritimorpha, are also land snails – although their closest relatives, such as the marine and freshwater nerites (Neritidae), prefer entirely different habitats.

Altogether, this means that several independent evolutionary lineages of gastropods have acquired the ability to live on dry land in their own unique ways. According to recent research, the transition to land has occurred independently ten to twelve times. While some groups, particularly the Stylommatophora, have left a rich fossil record, many other terrestrial snail groups are poorly represented or entirely absent in the fossil record.

Terrestrial Snails.
PONDER, W.F., LINDBERG, D.R. (2020): Biology and evolution of the Mollusca. Vol. 2., CRC Press, Boca Raton.
Warren D. Allmon & Jonathan R. Hendricks: Phylogeny and Classification of Extant Gastropoda.

Terrestrial Pulmonate Snails (Stylommatophora)

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Mouse-ear snail (Myosotella myosotis, Ellobiidae): Tasmania, Australia.
Picture: Bruno Bell (iNaturalist).		  
It is now widely accepted that the pulmonates (Pulmonata) and the former opisthobranchs share a common evolutionary origin. One key feature they have in common is the so-called detorsion – a reversal of the ancestral torsion of the body – as well as the complete loss of the operculum.

 
Slender dwarf horn snail (Carychium tridentatum).
Picture: Stefan Haller (schneckenfoto.ch).
Early representatives of the pulmonates include the coast snails (Ellobiidae), such as Myosotella myosotis, commonly known as the mouse-ear snail. This species is widely distributed along the European coastlines – from the North and Baltic Seas to the Mediterranean – and has been introduced to North America, Peru, Jamaica, South Africa and Tasmania (cf. iNaturalist).

Mouse-ear snails prefer grassy areas of saltmarshes, hiding under driftwood, stones, rotting seaweed or washed-up planks. They are highly tolerant of salinity and feed mainly on diatoms and detritus. In Germany, they are found exclusively in saltmarsh habitats – an increasingly threatened environment – and are therefore considered critically endangered.

NABU: Verstecktes Leben in der Salzwiese: Das Mäuseöhrchen im Porträt. (In German).
Arbeitskreis Mollusken NRW: Weichtier des Jahres 2008 Das Mäuseöhrchen Myosotella myosotis (DRAPARNAUD, 1801). (In German).

A characteristic feature of the Ellobiidae is the placement of the eyes at the base of the tentacles – in contrast to most other land snails (Stylommatophora), whose eyes are situated at the tips. There is strong evidence that a common ancestor of both Ellobiidae and Stylommatophora made the transition to land via coastal habitats. While coast snails like Myosotella remained in their original environment, some of their relatives, such as the minute dwarf horn snails (Carychiidae), ventured further inland. From this lineage, the terrestrial pulmonate snails proper (Stylommatophora) eventually evolved – a group that has successfully colonised a vast range of terrestrial habitats and undergone an extraordinary adaptive radiation.

This radiation not only makes the Stylommatophora the most speciose group of all gastropods, but also a major reason why the molluscs (Mollusca) – after the arthropods (Arthropoda) – are considered the second most speciose phylum in the animal kingdom.

GEYER, D. (1927): "Unsere Land- und Süßwasser-Mollusken", S. 131 f.; 3. Ed., K. G. Lutz-Verlag, Stuttgart.
WIESE, V. (2014): "Die Landschnecken Deutschlands", S. 35; Quelle & Meyer Wiebelsheim.
KERNEY, M.P., CAMERON, R.A.D., JUNGBLUTH, J.H. (1983): "Die Landschnecken Nord- und Mitteleuropas", S. 76 f.; Parey Verlag, Hamburg, Berlin.

Landdeckelschnecken (Pomatiidae)

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Round mouthed snail (Pomatias elegans): Not a pulmonate snail!
Picture: Gilberto Sánchez Jardón (iNaturalist): Asturias, Spain.		  
 
Round mouthed snails (Pomatias elegans) on wet rocks in the intertidal
zone. Picture: Florence Gully (Estran 22).
The round-mouthed snail (Pomatias elegans) is a widespread but habitat-selective species found in Western Europe and the Mediterranean region. It inhabits calcareous soils with sufficient humidity and plenty of hiding places. It feeds on dry leaves and decaying wood – and may even be capable of digesting cellulose.

At first glance, Pomatias elegans appears similar to the more familiar land snails. But on closer inspection, the similarities end there: Unlike the pulmonates, Pomatias elegans possesses an operculum that allows it to seal its shell, protecting itself from desiccation and predators, though this may be of little help against the Dalmatian predator snail (Poiretia cornea). Its eyes are located at the base of the tentacles, and its head bears a distinct snout. Furthermore, unlike most land snails, the species is dioecious, with separate sexes.

In fact, Pomatias elegans is not closely related to the pulmonates at all. It belongs to the Caenogastropoda, specifically to the Littorinimorpha – meaning its closest relatives are actually the periwinkles (Littorinidae). The oldest fossils of the genus Pomatias date back to the Oligocene, some 23 to 34 million years ago. This raises the question: How did the ancestors of Pomatias elegans make the leap to land?

A look at the behaviour of modern periwinkles offers some insight: Along the coasts of the North Sea and the French Atlantic, different species of Littorina occupy distinct parts of the intertidal zone. Many are well adapted to periods of aerial exposure. They avoid desiccation by retreating into crevices or sealing themselves with their operculum – a defence also useful against coastal predators such as shorebirds.

Interestingly, Pomatias elegans itself has been observed foraging in the splash zone of rocky shores in Brittany (Département Côtes d'Armor; cf. Estran 22). The species appears to tolerate saline spray to some extent. It seems plausible, then, that the ancestors of Pomatias elegans were littorinid-like snails that gradually developed greater tolerance to terrestrial conditions – eventually remaining on land permanently and no longer needing to return to the sea.

The operculum, originally a marine adaptation, remained in place and became even more important – now serving as protection not only against dehydration but also against the many predators encountered on land. One such predator, the aforementioned Dalmatian predator snail (Poiretia cornea), has evolved a particularly specialised method to overcome the operculate defences of its prey: Using a gland on its foot, it secretes an acidic substance that dissolves the shell wall, allowing it to consume the snail within, which is left with no means of defence.

Wikipedia: Pomatias elegans.
WoRMS: MolluscaBase eds. (2025): Pomatiidae R. B. NEWTON, 1891 (1828).
Estran 22: Faune et flore de la zone de balancement des marées en Côtes d'Armor: Mollusques (Französisch).
FECHTER, R., FALKNER, G. (1989): "Weichtiere", S. 122. Mosaik Verlag, München.
KERNEY, M.P., CAMERON, R.A.D., JUNGBLUTH, J.H. (1983): "Die Landschnecken Nord- und Mitteleuropas", S. 67 f.; Parey Verlag, Hamburg, Berlin.
WIESE, V. (2014): "Die Landschnecken Deutschlands", S. 33; Quelle & Meyer Wiebelsheim.

Turret Snails (Cochlostomatidae)

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Lesser turret snail (Cochlostoma septemspirale) with two door snails
(Clausiliidae):  Rhône-Alpes, Frankreich.
Picture: Guillaume Hoffmann (iNaturalist).		  
Cochlostoma septemspirale.
Picture: H. Zell (Source). 		  
 
Grey turret snail(Cochlostoma henricae): Bad Ischl, Salzkammergut,
Austria. Picture: Martina Eleveld
   
 
Forest needle snail (Aciculidae): Serpiano, Ticino, Switzerland.
Picture: Stefan Haller (schneckenfoto.ch).
Another group of land snails with opercula are the turret snails (Cochlostomatidae). The most widespread species in Central Europe is Cochlostoma septemspirale, a characteristic inhabitant of calcareous outcrops. The genus was first described by LAMARCK in 1799 as Cyclostoma, referring to the round shape of the aperture ("circle mouth"). Fossils of the family have been recorded as far back as the Palaeocene (66 to 56 million years ago).

Originally distributed in southern Europe – from the southern Pyrenees to the Balkan Peninsula – Cochlostoma septemspirale has also spread to several locations north of the Alps, including the Upper Rhine Valley, the Wutach Gorge, the southeastern Bavarian Alps and the Danube Valley near Regensburg.

The species prefers exposed limestone rocks, scree slopes and leaf litter in shaded forests. It can be found in both dry and humid habitats and feeds on algae, lichens and decaying plant material. After rainfall, these snails often appear in large numbers on bare rock, pieces of wood or bark, grazing on surface growth. In dry conditions, they retreat under stones or into dead wood.

A closely related species, Cochlostoma henricae, occurs in northern Italy (Southern Alps) and south-eastern Austria (Eastern Alps), with isolated populations also found in the Salzkammergut (Western Austria). It is typically found on limestone outcrops and is considered particularly drought-tolerant.

Like Pomatias elegans and other land snails with opercula (see above), the forest door snails are not pulmonates. They possess a solid, calcareous operculum, only two tentacles with eyes at the base, and separate sexes. Systematically, they belong to the Caenogastropoda – but unlike Pomatias, they are placed in the order Architaenioglossa, alongside freshwater snails such as the apple snails (Ampullariidae) and the river snails (Viviparidae).

Another terrestrial family within this group are the needle snails (Aciculidae). These tiny snails live mostly under leaf litter, stones, logs or within the soil – and sometimes in caves. Unlike most other land snails, many Aciculidae are believed to feed primarily on the eggs of other snails. As fossil relics of the Tertiary period, they can be traced back to the Eocene (56–33.9 million years ago; BOETERS et al., 1989).

As with Pomatias, the question arises: how did these snails make the transition from aquatic to terrestrial life? Given their close relationship to the Viviparidae, it seems likely that their ancestors lived in lakes and rivers and gradually adapted to life on land via swampy, seasonally dry habitats. Retaining the operculum would have been highly advantageous – helping to avoid desiccation and protect against predators in the new terrestrial environment.

An interesting comparison can be made with the apple snails (Ampullariidae), also part of the Architaenioglossa. These freshwater snails possess both gills and secondary lungs – an adaptation to waters that frequently dry out. They also have a siphon-like breathing tube, similar to those found in many marine snails, enabling them to breathe air when water levels drop. It is thus quite conceivable that the turret snails and needle snails may have evolved from a similar amphibious ancestor.

WoRMS: MolluscaBase eds. (2025): Cochlostomatidae KOBELT, 1902, Aciculidae J. E. GRAY, 1850
Wikipedia: Cochlostomatidae, Aciculidae.
Stijn Ghesquiere: Ampullariidae Respiration.
BOETERS, H.D., GITTENBERGER, E., SUBAI, P. (1989): "Die Aciculidae (Mollusca: Gastropoda Prosobranchia)". Zoologische Verhandelingen, 252(1): pp. 1–230.
FECHTER, R., FALKNER, G. (1989): "Weichtiere", S. 116 f., S. 126 f.. Mosaik Verlag, München.
KERNEY, M.P., CAMERON, R.A.D., JUNGBLUTH, J.H. (1983): "Die Landschnecken Nord- und Mitteleuropas", S. 63 ff., S. 69 ff.; Parey Verlag, Hamburg, Berlin.

Helicinidae

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Helicina striata:  Puerto Rico.
Picture: Octavio Rivera Hernández (iNaturalist).		  
The Helicinidae, last but not least, represent yet another group of land-dwelling operculate snails. They are virtually unknown in Europe, although more than 500 species have been described worldwide. Their distribution includes tropical and subtropical regions of the New World – for example, the southeastern United States (including Florida and Louisiana) – as well as various Indo-Pacific islands, and coastal regions of Asia and Australia. In tropical habitats, they often make up a significant proportion of the local mollusc fauna, both in terms of speciosity and abundance.

Ira Richling: helicina.de: Helicinidae research.

Helicinids inhabit a wide range of environments, particularly moist tropical forests. They are typically found in leaf litter, under decaying wood, or on tree trunks, and some species show a strong preference for calcareous soils. On the Caribbean island of Dominica, for example, Helicina rhodostoma has been recorded on ferns and tree bark as well as among rocks and gravel. Helicina guppyi, also found on Dominica, prefers tree trunks, where its colouration provides effective camouflage. In Florida, Helicina clappi is sometimes referred to as the "Rainbow Drop" because of its strikingly colourful shell.

 
Helicina unizonata:  Orellana, Ecuador.
Picture: Stephen Luk (iNaturalist).		  
Helicina laus: Río Cuyabeno, Putumayo, Sucumbíos, Ecuador.
Picture: Felipe Campos (iNaturalist).
The shells of many Helicinidae resemble those of the more familiar Helicidae (garden snails) – as their name might suggest – but the similarities end there. Like the other groups described above, helicinids are not pulmonates. They possess a solid calcareous operculum, have separate sexes, and feature two tentacles with eyes at their base. Systematically, they do not belong to the Caenogastropoda, but instead to the Neritimorpha – and are thus more closely related to marine and freshwater nerites (Neritidae).

This again raises the question of how these snails made the transition to a terrestrial lifestyle. According to Dr Ira Richling (helicina.de), helicinids are "a group of snails which were among the first to evolve a terrestrial lifestyle, independently of other and usually better-known groups such as the pulmonates”. She also notes that “despite these interesting features, they have largely been neglected as a subject of research".

Many nerite species inhabit transitional zones between water and land. Some, like the freshwater nerite Theodoxus fluviatilis, tolerate brackish water up to a certain salinity level and can even be found along the Baltic Sea coast. Others, such as Nerita lineata, are common in Singapore’s mangrove swamps and seasonal drainage channels (see: Guide to the Mangroves of Singapore: Common nerite). Against this background, it seems plausible that the Helicinidae may have evolved from amphibious ancestors similar to modern nerites – snails that gradually made the transition from coastal and mangrove habitats to a fully terrestrial existence.

One thing is certain: despite the similar-sounding names, Helicinidae and Helicidae could hardly be more different!

ROBINSON, D.G., HOVESTADT, A., FIELDS, A., BREURE, A.S.H. (2009): "The land Mollusca of Dominica (Lesser Antilles), with notes on some enigmatic or rare species". Zoologische Mededelingen 83. (Link).
Wikipedia: Helicina rhodostoma, Helicina guppyi.
Jacksonville Shell Club: Florida Land Snails Part 2.

 


With pictures by Stefan Haller:
http://www.schneckenfoto.ch.

Latest Change: 26.09.2025 (Robert Nordsieck).