Round mouthed snail (Pomatias elegans), dis-
playing its proboscis and operculum.
Picture: © Stefan Haller (schneckenfoto.ch).
Family: Pomatiidae Newton 1891
Source: Mollbase on http://www.mollbase.de/list/.
Round mouthed snails are quite different from a large part of the terrestrial snails we know. Their external appearance resembles more to a mud snail (Viviparidae) from a lake or river (to which they are not related), and to snails living in the sea.
Round mouthed snails possess a shell lid (operculum); their head is extended to form a distinct trunk (proboscis) and their eyes are located are the tentacles' base. Besides, round mouthed snails, contrary to most other terrestrial snails, have separate sexes, there are males and females.
Schöne Landdeckelschnecke (Pomatias elegans) mit der typisch
"zweifüßigen" Fortbewegung (beachte die Rolle der beiden Fuß-
hälften. Film: Martina Eleveld (YouTube).
A very distinct character is the way round mouthed snails move, which is quite different from the crawling motion of a pulmonate snails, as shown by a Roman snail. A pulmonate snail crawls by a wave-like motion of the entire foot sole. The locomotion of round mouthed snails, on the other hand, is a "bipedal" one, so to speak: They put one half of the foot in front after the other. So in English they are also called "shuffler snails".
And actually, one view on the systematic classification of the round mouthed snail family shows that they are more closely related to periwinkles (Littorinidae), than to other terrestrial snails.
Head of Pomatias elegans. 1: Eyes; 2: Tenta-
cles; 3: Proboscis; 4: Pneumostome; R, L:
Right and left halves of the foot.
Picture: Martina Eleveld.
Looking at different groups of terrestrial snails, many signs point towards the fact that the transgression to dry land from the sea took place several times in the evolutionary history of snails. Even today, round mouthed snails still sometimes live in coastal habitats near the sea, where they are directly exposed to the salty water. Only a little distance away, in the water, their marine relatives, the periwinkles, have their habitats. Of course, "modern" periwinkles and round mouthed snails are not those snail groups, which have performed the transgression on land millions of years ago. But this view gives a bit of an idea, what it might have looked like.
In systematics, there appears to be uncertainty, whether the name of round mouthed snails ought to be Pomatiidae or Pomatiasidae. Concerning the declination, Pomatiasidae is impossible, following the Rules of Nomenclature, the family ought to be called Pomatiatidae, at least in this author's opinion. The Latin genitive of Pomatias is Pomatiatis, see also Cochlostomatidae. However, according to Mollbase the correct name to use is Pomatiidae.
Round mouthed snails are by no means the only operculate family of terrestrial snails. Among those there are different groups, not necessarily more closely related to each other, apart from being snails: Cochlostomatidae as well as Needle Snails (Aciculidae) are some of them. Several species of round mouthed snails are present in Western Europe and in the Mediterranean. Usually, they are species of temperate to warm habitats.
Terrestrial operculate snail (Tudorella sulcata) from southern France (left) and Sicily (right).
Pictures: Daniel Pavon (left, Source) and Francisco Welter-Schultes (right, Source).
Apart from the genus Pomatias (Pomatias rivularis in South-eastern Europe and Turkey, Pomatias glaucus in Turkey and Cyprus, Pomatias olivieri in Israel and the Lebanon), in Western Europe, for example, there is the genus Tudorella.
The terrestrial operculate snail Tudorella sulcata, is present in South-eastern France, Southern Spain and Southern Portugal, also in Corsica, Sardinia, Sicily, Malta, as well as in the East of Algeria. By using genetic markers, scientists were able to find out that this snail species has been distributed in the Western Mediterranean by Neolithic human trade routes.
Before, it had been assumed that the species had been distributed only by the tectonic drift of continents, a theory which is not coherent with the results of genetic examinations.
Kontinentaldrift als Schneckentaxi (Continental drift as snail taxi, German) (10.12.09)
Scinexx: Landschnecken auf Seefahrt (Terrestrial snails take to the Sea, German) (30.06.11).
Francisco Welter-Schultes: Tudorella sulcata species homepage.
Tropidophora ligata (?), a relative of the round mouthed snail
from Madagascar. Picture: Martina Eleveld.
However, the largest part of the round mouthed snails' relatives is not to be found in the Mediterranean, but in tropical and temperate warm climates of the Old World. Especially the Tropidophora genus can be found at the African east coast and on Madagascar with a very large diversity of species. Sometimes, those snails, some of which can have a rather spectacular appearance, can be kept in a terrarium.
Martina Eleveld: A movie of Tropidophora cf. ligata on YouTube.
Herbert, D.; Kilburn, D. (2004): Field guide to the land snails of eastern South Africa; p. 93 ff.
As one member of the family, the round mouthed snail, present in Central Europe, Pomatias elegans, shall be described. It also is the most frequent European member of the family.
Round mouthed snail - Pomatias elegans (O. F. Müller 1774).
Round mouthed snail (Pomatias elegans).
Picture: © Alexander Mrkvicka, Vienna (mrkvicka.at).
Description: The round mouthed snail has got a moderately slender shell of a reddish colour with a whitish flame pattern. The shell surface is covered in distinct ribs parallel to the coiling of the whorl. Transversal stripes or striae crossing those ribs make a distinct network sculpture. Also especially distinct are the shell whorls, having a nearly circular profile. The shell tip (apex) is pointed. Males and females are different in shell size and whorl profile: Males usually are smaller than the females, also the latter have more rounded whorls with a larger width.
The snail's soft body is rather large and coloured brownish grey. The tentacles, at whose base the eyes are located, are long, quite cylindrical and striped transversally.
Dimensions: H: 13 - 18 mm; W: 9 - 12 mm; N: 4 - 5. (Abbreviations).
Habitat and Distribution: The round mouthed snail is an inhabitant of open forest and bush landscapes. It prefers loose calcareous ground, into which it can dig itself to aestivate for at least 10 cm (4 in.). Pomatias elegans feeds on dead leaves and decaying wood. It prefers dry leaves to wet ones. Probably with the help of symbiotic bacteria, the snails can also digest cellulose.
Round mouthed snails (Pomatias elegans).
Picture: © Alexander Mrkvicka, Vienna (mrkvicka.at).
The distribution area of the round mouthed snail spreads from Western Europe to Southern Europe and the Mediterranean as far east as North-western Turkey. While in the North, the species' distribution area reaches as far as England and Denmark, and in the North-east to Central Germany, the round mouthed snail also occurs in Northern Africa and was introduced on the Balearic island of Minorca. In Germany, the round mouthed snail is present only in warmer regions, such as in the Kaiserstuhl near Freiburg, near Heidelberg, Bonn and Jena, as well as in the valleys of Moselle, Ahr, Weser and Unstrut.
Round mouthed snails (Pomatias elegans) in the supralittoral
zone in Brittany, exposed to salt water.
Picture: Florence Gully, Gastéropodes 2.
In the North, the round mouthed snail's distribution is limited by the 2°C-January-isothermal, in the altitude the limit is 1300 m above MSL, in Switzerland 1000 m MSL and in Bulgaria 900 m MSL.
While the snails are still active around 8°C, they need a higher temperature to wake up. Hibernation round mouthed snails can endure lower temperatures near -6°C. Also the round mouthed snail's resistance against dryness is remarkable: The snails can survive several months of dryness, remaining in an inactive state during that time. But 30 minutes after the first contact with water, they regain activity. Though they need a higher humidity to wake up from aestivation, the snails can only survive for 4 weeks at most on constantly wet soil.
Round mouthed snails mate between spring and autumn. But not until autumn, the snails lay about 50 to 60 single eggs in the ground. Each egg is covered in a mucus layer binding earth particles and so camouflaging itself. In Central Europe the eggs hibernate, after three months, the juveniles hatch with two whorls and 2 mm shell height. Round mouthed snails can grow to an age of four or five years.
Threat Situation: Especially in Central Europe, the round mouthed snail is threatened by intensive agriculture and viticulture, together with the destruction of its habitats und its impairment by fertilizers and insecticides. In Central and Eastern England the species has strongly decreased. While it is classified as endangered in Switzerland and Ireland, in Germany the round mouthed snail is classified as vulnerable (see also IUCN Threat Categories).
Pomatias elegans species homepage.
Molluscs of Central Europe: Pomatias elegans on mollbase.org.
Species description of Pomatias elegans) in the forum schnecken-zone.de (in German).
Discussion on round mouthed snails (Pomatiasidae) in the forum "Achatschnecken vom Wienerwald" (in German).
Fabrizio Vicente: Pomatias e Littorina: l'Evoluzione raccontata da due chiocciole in the forum Mondo Gasteropodi (in Italian).
Aydin Örstan: Land Snails of Turkey: Pomatias elegans.
Falkner, G. (1990): "Weichtiere"; p. 122, 123 (1-2,4-5) (in German).
Lais, R. et al.: "Die Mollusken", in: "Der Kaiserstuhl - Eine Naturgeschichte des Vulkangebirges am Oberrhein", Bad. Landesverband f. Naturkunde u. Naturschutz, 1933, p. 366 ff (in German).
With pictures by Stefan Haller: