gastropods colonize various kinds of waters including lakes, rivers, brooks,
ponds, and even small earth holes temporarily filled with water. In
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
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
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
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,
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).
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.
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Published in the March 2007 edition of Micscape.
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