reshwater gastropods colonize various kinds of waters including lakes, rivers, brooks, ponds, and even small earth holes temporarily filled with water. In Central Europe, aquatic snails occur in both the alpine foreland and the inner-alpine regions, thereby partly occupying small waters positioned in about 3,000 metres above sea level (nival altitude level). With increasing geographic altitude of the colonized habitats the number of gastropod species, termed species diversity, on the one side and the number of individuals per species, termed specific abundance, on the other side are subject to a dramatic decline (Sturm, 2004). Freshwater gastropods develop two main strategies for a successful colonization of a habitat and dispersal to biotopes not occupied so far: While generalists do not have any specific demands on their environment and thus can be found in waters with high or low contents of nutrients, dense or sparse submerged vegetation, attractive or detractive physico-chemical conditions, specialists only occur, if their habitat fulfils very specific conditions (e.g. dense submerged vegetation, water temperature above 20 °C, water ph not lower than 6 and not higher than 8).

After this small ecological excursion, some words should be also written about the size and sampling of freshwater gastropods. The size of the shells ranges from few millimetres to about five centimetres (see also the examples exhibited below). Since most species develop shells with a size of about 1 cm, it is not so easy to find them in their habitats. The sampling of animals is additionally complicated due to the fact that they are either hidden in the sediment or fixed on the stalks and leaves of plants. Hence, sampling work has to be conducted very carefully using specific equipment such as a hand sieve, feather tweezers, a magnifying glass, etc. In Austria most aquatic gastropods belong to the so-called Red List meanwhile. This means that they are partly endangered by extinction and may be only sampled with a special permission (e.g. for malacological research; e.g. Sturm 1999, 2004).

In this small contribution, shells of some freshwater gastropods living in Central-European waters are presented. The shells were picked up during a malacological field study carried out some years ago. To especially express the plasticity and volume of single shells, stereograms based on the anaglyphic concept, where three-dimensional information is recorded in two superimposed colour layers (red and cyan), were produced.

 

 

 

tereographic photography represents a well defined procedure meanwhile and therefore will be described only with few words which are necessary in this specific context. Before starting with photography, the object has to be fixed on the underground using either wax, some modelling clay or, if none of both is available at short notice, a chewing gum. The shell should be mounted in the way that its spindle axis is aligned vertically and, in the case of a front view, its orifice is perfectly visible. After the mounting procedure the object is photographed from two different positions separated by an angle of 5 to 7 ° (Figure 1). Photography of larger gastropod shells is conducted with a digital camera selecting the ‘macro’ setup, while small shells are photographed either with a magnifying glass placed in front of the camera objective or under a stereomicroscope. Combination of the two photographs takes place by specific software for the production of anaglyphs which may be downloaded from the internet for free. Another way for the production of anaglyphic stereograms is given by the Adobe Photoshop©, where pictures may be trimmed and superimposed in a very elegant way (Russ & Russ, 2005).

 

 

 

Figure 1 Photographing procedure necessary for the production of stereographic images. The object has to be photographed from two different camera positions which are separated by an angle of 5 to 7 ° (left sketch). On the right side, ‘raw’ photographs of Valvata piscinalis and the respective anaglyphic image are shown. For an appropriate recognition of the three-dimensional effect, anaglyphic glasses (left: red, right: blue) are required.

 

 

 

 

 

 

 

 

 

 

 

 

 

n the following section, 3D-photographs of gastropod shells, which can be sampled from Central-European waters, are presented and described in detail. Besides the photographs themselves also some ecological information is provided (see Glöer & Meier-Brook, 2003), giving an idea about which habitats are preferentially colonized by the animals and if the snails may be categorized as generalists or specialists.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2 Front and back view of the two biggest freshwater gastropod species occurring in Central-European waters. On the left side Viviparus contectus is shown, whose shell reaches a height of about 5 centimetres, while on the right side Lymnaea stagnalis is depicted, the shell of which may reach a size of about 4.5 centimetres.

 

Viviparus contectus: The shell consists of 6 to 6.5 whorls separated in a stepwise fashion. Each whorl shows three reddish brown bands being a characteristic for Viviparus. The gastropod is characterized by a high variability concerning its size and colour. From an ecological point of view, the snail preferably colonizes ponds, moor lands and swamps enriched with vegetation, but also occurs in rather acidic waters. In Central Europe the abundance of this gastropod varies significantly.

 

Lymnaea stagnalis: The shell of the snail is unusually long with a peaky top. The 7.5 whorls rapidly increase in size, whereby the last whorl is often significantly enlarged (‘blown up’). Lymnaea shows high variability regarding the shape of its shell. The gastropod primarily colonizes the shores of large ponds and lakes being rich of submerged vegetation. It can be found in a maximum depth of 6 metres and further tolerates salt concentrations up to 0.7 percent, underlining its preferential character as specialist.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3 3D-Photographs of front and back views of the pulmonal gastropods (family LYMNAEIDAE) Radix ampla (left) and Radix balthica (right). The shells of both snails are one category of size below those of Viviparus and Lymnaea. While Radix ampla reaches a size of 1.8 centimetres, maximum size of Radix balthica is about 1.5 centimetres. For obtaining satisfactory photographic results both shells have to be recorded using an excellent macro objective or a magnifying class.

 

Radix ampla: Except for the last whorl, the spindle of the shell is very small. The orifice of the shell is very impressive, occupying more than 50 % of the overall volume. The gastropod may be characterized as a specialist that colonizes waters in the alpine foreland, but does not occur in any mountain lakes.

 

Radix balthica: The shell of this gastropod consists of 4.5 whorls which show a convex contour line and increase their volumes very quickly. The shape of the shell is marked by high variability, so that determination in the field is complicated sometimes. The snail mainly colonizes small lakes or ponds being highly enriched with submerged vegetation, whereas in larger waters individuals are limited to the shore area. Radix balthica is evaluated as the most adaptable gastropod species in Central Europe, thereby also occurring in high-alpine waters (above 2,700 metres above sea level).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4 3D-Photographs of the front and back view of two quite small-sized freshwater gastropods found in Central-European waters. Radix labiata (left) belongs to the LYMNAEIDAE and reaches a maximum size of 1 centimetre, whereas Bithynia tentaculata (right), which may close its orifice with a so-called operculum, has a size of about 0.5 to 0.8 centimetres. Photography of both snails has to be regarded as rather difficult and is therefore best conducted with a stereomicroscope with respective photographic equipment.

 

Radix labiata: The shell of this very frequently occurring gastropod consists of 4.5 to 5 whorls which are very uniform in shape and increase rather slowly. The colour of the shell is medium to dark brown. Although the shape of the shell can be evaluated as very stable among a high number of subjects, Radix labiata is hardly distinguishable from Radix balthica in some specific cases. Concerning its ecology, the aquatic snail primarily colonizes small ponds and brooks, but can be also found in moor lands and high geographic altitudes (- 2,500 metres).

 

Bithynia tentaculata: The shell of this gastropod consists of 5.5 whorls which are separated by a clearly visible suture. Bithynia mainly colonizes lakes and moderately flowing waters not exceeding a salt concentration of 1.2 percent. The species may be regarded as very adaptable and unpretentious and therefore can be assigned to the group of generalists. In Central Europe the aquatic snail is characterized by a partly high abundance, and single occurrences of the species in waters positioned 2,000 metres above sea level were reported.

 

 

 

rom the brief study presented here it can be concluded that 3D-photography represents a useful and partly spectacular technique in diverse biological disciplines. Concerning the scientific field of malacology (i.e. science of terrestric and aquatic molluscs), with the help of anaglyphic photographs shells of gastropods and bivalves can be described in a better and more impressive way. The work has to be understood as an impulse for all those people, scientists as well as hobby biologists, who like to photograph small objects. By the application of 3D-photography, the research of small animals or plants is certainly enriched by a further interesting facet.

 

 

 

• Glöer, P. & Meier-Brook, C. (2003): Süsswassermollusken. - DJN, Hamburg, 137 p.
• Russ, J. C. & Russ, J. C. (2005): Assembling Stereo Anaglyph Images with Photoshop. – Modern Microscopy Journal 6/2005.
• Sturm, R. (1999): Die Wasserschnecken und Muscheln in einem Nebenarm der Königsseeache (Bundesland Salzburg). – Ein Beitrag zur Wassermollusken-kartierung im Tennengau. – Linzer biologische Beiträge 31/2, 739-745.
• Sturm, R. (2004): Freshwater Molluscs (Gastropoda et Bivalvia) in selected Mountain Lakes of the Hohe Tauern, Austria: A Contribution to the Faunistic Mapping of the Eastern Alps. – Malakologische Abhandlungen (Dresden) 22, 23-36.