River cap snail
| River cap snail | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
River cap snail ( Ancylus fluviatilis ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Ancylus fluviatilis | ||||||||||||
| OV Müller , 1774 |
The river cap snail ( Ancylus fluviatilis ), also called river limpets , is the best known and in Central Europe only species of the genus Ancylus . Today it is part of the family of poppy snails (Planorbidae); previously it was assigned to the now dissolved family "Ancylidae". In addition to rivers and other rivers, it occurs on the rocky or stony subsoil of some lakes.
features
Morphology : The river cap snail, with a maximum shell length of 11 mm (mostly adult only 5–8 mm), is a small to medium-sized adult , but in some places common and widespread water lung snail (Basommatophora). The larger forms (over 8 mm) occur in Central Europe only in relatively calcareous streams with optimal nutritional and temperature conditions (e.g. near Lake Constance). Its bowl-shaped bowl with the tip slightly turned to the right and back is characteristic; the apex of the shell shows roughly sculpted radial ribs. When hatching, the animals measure less than 1 mm shell length.
Karyology : Compared to the majority of the other cup-shaped representatives of the Planorbidae, the species is characterized by an increased number of chromosomes . While the haploid chromosome set in the majority of these species and genera, as far as they have been investigated (especially Rhodacmea cahawbensis , Laevapex fuscus ; not in Ferrissia species) is n = 15-17, which is within the basic equipment of all water pulmonate snails (n = 15- 18), it is n = 30 for Ancylus fluviatilis ( tetraploid , sometimes n = 60 ( octoploid ) were reported).
Similar species
On the surface, the river cap snail resembles the pond limp. However, this is anatomically twisted to the right. The apex of the shell of the river cap snail therefore points to the rear right, and of the pond limpet to the rear left.
Another possibility of confusion, especially of juvenile river cap snails, exists with the species, which may have been introduced from North America, but perhaps also from other regions of Europe and is traditionally referred to as Ferrissia wautieri (the exact assignment and naming is currently unclear). This species, like the river cap snail, has a left-handed shell, but is only 3–4 mm long, tends to have a rather elongated shell and sometimes forms a septum on the underside of the shell after dry phases.
Geographical distribution and species status
The species is distributed over large parts of western, central, eastern and northern Europe (to southern Sweden, Norway and Finland). The forms that occur in large parts of the Mediterranean region (Iberian Peninsula, Italy, etc.) and which have so far been nominally also referred to as Ancylus fluviatilis are, according to molecular genetic findings, independent forms that at least have the kinship status of their own species, but which so far have not been named independently are. In addition, occurrences of this group of forms in northeastern Africa (coastal areas from Morocco to Tunisia, Hoggar Mountains in Algeria) and in the highlands of Ethiopia up to 2240 m above sea level are reported. For more details cf. also under the genus Ancylus .
Ecological spread
The snails occur in oxygen-rich standing and flowing waters and also in karst springs . In any case, they needed a hard substrate with suitable (not too little and not too lush) algae growth, which is why they are common in Central Europe, especially in rivers, but also occur in lakes (even widespread in Northern and Western Europe). In contrast to many other freshwater snails, the animals can also tolerate a low-base acidic environment. With a saprobic index of 1.8, they are considered a pointer species for water quality class II in Germany.
Southern European, North African and Near Eastern representatives of the species group can probably survive drying of the waters to a certain extent by forming a protective layer on the underside of the shell; In the case of the Central European forms, this is only possible to a limited extent and for a short time by means of strong, water-saving stapling to the stone substrate.
Way of life
Diet : The river cap snail feeds on vegetal growth ( periphyton ) and detritus , whereby diatoms , small green algae , locally also aquatic lichens and other food components are absorbed and digested. The chopping and digestion of the diatoms are supported by the numerous grains of sand stored in the gizzard, which are absorbed and stored during the eating process. The animals consume between 1 and 5% of their own body mass in the active feeding phases, but repeatedly take breaks from eating (see following section).
Activity : The animals move over rocks, scree and bedrock, showing rest or activity phases at irregular intervals (without a recognizable day-night rhythm). They spend the rest phases, which often last many hours, on the underside of the rocks (which is more protected from the influence of predators), while they move over the rocks in a largely non-directional random pattern to actively graze on the food. Wherever there is food in a suitable composition and thickness that can be ripped off with the radula, it remains and grazes more or less completely through alternating head movements with simultaneous slow crawling forward. In the winter months, the animals often remain in a state of rest for a long time, which is also a state of reduced metabolic activity.
Propagation biology : The irregular phases of activity with periods of immobile persistence and intensive grazing in nutritionally favorable places also serve the expansion in the water and the finding of the often patchy, favorable small habitats. As a result, the individual animal can get up to 1 m or more from the place of hatching in the course of a year. Orientation and expansion are obviously random; only a slight component of an upstream direction can be measured. The spatial expansion thus corresponds to the principle of diffusion . However, "long-distance transport" of river cap snails has also become known, especially due to the accidental attachment to the feet of water birds or the bodies of larger, airworthy water beetles. The most famous observation of being pinned to beetles is that of Charles Darwin in his book " The Origin of Species " (p. 386 of the original English edition). This form of spreading is more important in the long term (e.g. in the case of the repopulation of formerly glaciated areas after the Ice Ages ) compared to the diffusive local spreading, which is used for the gradual settlement of a larger stretch of water after a first local settlement.
Reproductive biology
The river cap snail is hermaphroditic like all water snails , whereby one partner can act as a male and the other as a female during copulation . Copulation chains of four to five animals lying on top of one another have also been described, in which the uppermost only function as a male, the lowest only as a female and everyone in between functions as both males and females.
However, further studies showed that in many populations there is a pronounced tendency towards self-fertilization . By measuring polymorphic allozyme loci it was concluded that only 13 to 15% of the juvenile snails had emerged from cross-fertilization and that even when copulations were observed externally, the use of one's own sperm must often be expected. The ability to self-fertilize is in principle a survival advantage, since even single animals can build up a population again.
The eggs are laid in the form of several gelatinous egg capsules of 1-10 eggs each (on average around 5-7 eggs) at intervals of a few days. The beginning of copulation and oviposition usually occurs from a shell length of 4 to 5 mm. After the beginning of the egg-laying, the body's growth is reduced to around 1/5 of the growth rate compared to the previous growth, but it still continues. The number of eggs per capsule depends on the size of the adult and the nutritional status. The total number of eggs laid per adult is highly variable and is a maximum of over 100 eggs. Egg-laying begins in spring from a temperature of 7 to 10 ° C.
paleontology
As a key fossil in the area of today's Baltic Sea , it led to the naming of the Ancylus Sea .
Individual evidence
- ^ Christian Albrecht, Kerstin Kuhn & Bruno Streit: A molecular phylogeny of Planorboidea (Gastropoda, Pulmonata): insights from enhanced taxon sampling. Zoologica Scripta, 36: 27-39, Oxford, 2007.
- ↑ CM Patterson, JB Burch: Chromosomes of pulmonate molluscs. Pp. 171-217 in: V. Fretter, J. Peake: Pulmonates, Vol. 2A, Academic Press, London 1978
- ↑ B. Streit, B., T. Städler, K. Kuhn, M. Loew, M. Brauer, B. Schierwater: Molecular markers and evolutionary processes in hermaphrodite freshwater snails. Pp. 247-260 in: B. Schierwater, B. Streit, GP Wagner, R. DeSalle: Molecular Ecology and Evolution: Approaches and Applications. Birkhäuser Basel 1994
- ↑ Hubendick, B .: Studies on Ancylidae, the Palearctic and Oriental species and form groups. In: Acta Zool . 5: 5-52 (1970)
- ^ David S. Brown: Fresh Water Snails of Africa and their Medical Importance . 2nd ed., Taylor & Francis 1994.
- ↑ Meyer, Detlef .: Macroscopic biological field methods for assessing the water quality of rivers: with lists of species for beginning and experienced investigators and detailed descriptions and images of the indicator organisms . 4th, unchanged. BUND, Hannover 1990, ISBN 3-9800871-4-X .
- ↑ W. Schwenk, J. Schwoerbel : Investigations into the nutritional biology and way of life of the river cap snail Ancylus fluviatilis (OF Müller 1774; Gastropoda Basommatophora). Arch. Hydrobiol./Suppl. 42: 190-231 (1973)
- ↑ B. Streit: Experimental studies on the substance balance of Ancylus fluviatilis (Gastropoda - Basommatophora). 1. Ingestion, assimilation, growth and oviposition. Arch. Hydrobiol./Suppl. 47: 458-514 (1975)
- ↑ R. Geldiay: Studies on local populations of the freshwater limpet Ancylus fluviatilis Müller. J. Anim. Ecol. 25: 389-402 (1956)
- ↑ T. Städler, S. Weisner, B. Streit: Outcrossing rates and correlated matings in a predominantly selfing freshwater snail. Proc. R. Soc. Lond. B 262: 119-125 (1995)
Further literature
- Peter Glöer: The animal world of Germany. Mollusca I Freshwater gastropods of Northern and Central Europe Key to identification, way of life, distribution. 2. rework. Ed., 327 pages, ConchBooks, Hackenheim 2002 ISBN 3-925919-60-0
Web links
- Ancylus fluviatilis inthe IUCN 2013 Red List of Threatened Species . Posted by: Seddon, M., Albrecht, C. & Van Damme, D., 2010. Retrieved February 13, 2014.