Water louse
| Water louse | ||||||||||||
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Water isopods ( Asellus aquaticus ) |
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| Asellus aquaticus | ||||||||||||
| ( Linnaeus , 1758) |
The water louse ( Asellus aquaticus ) is a freshwater species from the order of the woodlice . Only four species of woodlice are found in Central European surface waters, three of which are neozoa introduced from south-east, south-west Europe and the Mediterranean . The water louse is the only native species. It is often found in standing and flowing waters of all kinds, but prefers nutrient-rich waters.
features
Male water lice reach a body length of 12 to 20 millimeters, the slightly smaller females 8 to 15 millimeters. The animals are usually gray to gray-brown in the basic color, with scattered white spots. Typically colored individuals can be identified by the pattern of the head up to the species: When viewed from above, this is gray with two large, white spots, which are separated by a broad, darker longitudinal band. Untypically colored or very light-colored animals (often in subterranean waters) can be distinguished from the other European isopods of the genus Proasellus by the typical shape of the second pleopods, the inner chest of the maxillula and the circular, mutually overlapping second pleopods of the females .
The body of the water louse is flattened dorsoventrally (from top to bottom) and oval shaped when viewed from above, about 2.8 times as long as it is wide. The head is a little more than twice as wide as it is long, it has two small, dark complex eyes that only consist of three to four ommatidia . When viewed from above, three body regions (tagmata) can be seen: The head section is followed by seven separate segments of the trunk section ( peraeon ), followed by a pleotelson (from the pleon and telson ) fused to form a uniform, rounded rectangular plate . On the head there are two pairs of antennae (as is typical for crustaceans), the first of which is about a third and the second almost body length. When viewed from below, it can be seen that the pair of extremities of the first trunk segment connects to the head as a maxilliped and is not used for locomotion, but for eating. The seven pairs of legs (peraeopods) are long, they increase in length from front to back. The first Peraeopod is designed as gripping scissors ( Chela ), in which a movable finger can be folded like a pocket knife against a solid base member. The remaining pairs of legs have a strong claw at the end. The sexes can be distinguished by the shape of the extremities of the abdomen, the pleopods; the pleopods of the male are the only organ that allows a reliable determination of the species. In both sexes, the exopodite of the third pleopod is enlarged and forms a large lid (operculum), the protects the gills. In front of it sit two small pleopods in the male and only a pair of small pleopods in the female (here the first have been lost). In the species, the male's first pleopod is almost as long as the second. The exopodite of the first is rounded to oval. In the second pleopod, the last segment of the exopodite is broadly rounded and shorter than the endopodite, which has a distinct extension on the inner edge. The shape of the pleopods can only be seen with a strong magnifying glass or under the binocular . At the end of the body, two extremities, the uropods , protrude far back (they reach almost a third of the body length); these are designed as two-branched split legs typical of cancer .
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Reproduction
The females lay up to 100 eggs, which are carried in the brood sac. The young woodlice swarm out after 3 to 6 weeks and are already similar to the adults.
habitat
Water isopods live in both standing and flowing waters , with all types of flowing water being colonized, from streams ( Rhithral ) to large rivers ( Potamal ) . They are therefore indifferent to currents in their large-scale distribution, but prefer clearly calm bays or areas with slow currents as microhabitats in flowing waters . They are found preferentially in lowland waters, where they live between aquatic plants or on organic detritus or dead wood , and more rarely on mud or sand. Cold and warm water bodies are equally populated (temperature indifference), but acidic bodies of water with a low pH value are clearly avoided. They can also live in brackish water with moderate salt loads. They feed on decaying plant residues, and they also scrape off the organic coatings ( periphyton or biofilm ) made of algae and bacteria from stones and other hard substrates. With high oxygen consumption in the water, they can survive for some time at very low oxygen concentrations or even under anaerobic conditions. With an index value in the saprobic system of 2.8, the water louse is a key organism for heavily polluted waters of water quality class III. If their residential waters dry out, they dig themselves into the mud. The woodlice can be found all year round, even at the bottom of frozen water.
behavior
Water lice move by walking, but can also swim in response to strong mechanical stimuli. They live on the ground or climb aquatic plants. The animals seem sluggish, but they can be very nimble in danger. They can withstand a stronger current and migrate against the direction of the current. They do not settle permanently in waters with current speeds of more than 5 centimeters per second. But this is mainly due to the fact that the flow conditions here do not allow sufficient deposits of dead plant parts as a source of food for the water isopods.
Like other inhabitants of macrozoobenthos , they are often used in the food chain as food for larger fish. They can transmit scratch disease to the fish if they themselves harbor scratch worms (Acanthocephala).
Water pipes
Water isopods are among those living things that can colonize the pipe network, especially in areas where nutrient-rich surface water serves as a source of drinking water. They feed on washed-in organic material and break down the biofilms that can form on the walls of the pipelines. An increased reproduction of the water isopods is therefore an indicator of increased pollution of the water. The woodlice themselves do not pose a health risk, in particular they do not spread any coliform bacteria into the pipe network. When taking control measures, care must be taken to ensure that the bacteria, fungi and unicellular organisms in the biofilms do not multiply faster than before after the waterwoods are washed out. In addition to the woodlice themselves, their droppings are also washed out into the drinking water. The control is done by flushing the pipes, whereby it is usually impossible to flush out all woodlice, as they retreat to hiding places when the current increases. Water isopods are a problem especially in North German drinking water networks. The cave isopods of the genus Proasellus , especially Proasellus cavaticus , which occur more frequently in southern Germany , are far less problematic because, as typical groundwater animals , they have a much lower rate of reproduction and are unable to develop mass occurrences.
Spread and endangerment
The water louse originally comes from Siberia. After the Ice Age it spread to the west and gradually colonized most of Europe. Asellus aquaticus seems to displace Proasellus meridianus and P. coxalis .
In Germany the water louse is by far the most common member of the Asellidae. The species is not endangered.
Taxonomy and systematics
The species was first described by Linné as Oniscus aquaticus , the original diagnosis “Oniscus cauda rotundata, stilis bifurcis” is unclear and could refer to any isopod species living in the water. Due to the distribution area (it is assumed that Linnaeus description referred to animals from Sweden) and the new description by Emil Racoviță in 1919, the name was generally referred to this species. Since the type material of both researchers has been lost and numerous forms and morphs have been described by other researchers, a neotype was established in 2009 and the species was rewritten. While the affiliation of the forms living in surface waters to the species is clear, numerous cave-living ( troglobionte ) or groundwater ( stygobionte ) forms with slightly different morphology have been described from cave waters in the Dinaric Karst , in which the pigmentation, partly also the eyes, has regressed , including the subspecies Asellus aquaticus cavernicolus Racovitza, 1925 and Asellus aquaticus cyclobranchialis Sket, 1965. Since the subterranean forms of the species have been treated by different authors according to different systematics and the morphologically and genetically defined units do not match, the structure of the species and the Number of subspecies currently unclear. In 2009 another troglobionte form from the border river Reka / Timavo , which had previously been included in the species, was re-described as the new species Asellus kosswigi . There are also known populations of the water louse from other regions, including Central Europe, living in groundwater or cave waters, which can usually not be distinguished morphologically from those from surface waters.
The genus Asellus is distributed with almost 20 species, mainly in East Asia and Japan, including numerous species that live in underground waters. The water louse is the only species of the genus in Europe and the Western Palearctic that lives in surface waters.
Web links
Individual evidence
- ↑ Herbert Zucchi & Karin Zucchi (2005): On the ecology and determination of the three woodlice species (Isopoda: Asellidae) occurring in Germany in flowing waters. Microcosm 94 (2): 89-91.
- ↑ Karel Wouters & Thierry Vercauteren (2009): Proasellus coxalis sensu auct. (Crustacea, Isopoda) in a lowland brook in Heist-op-den-Berg: first record in Belgium. Lauterbornia 67: 53-61.
- ^ A b c Hans-Eckhard Gruner: Crustaceans or Crustacea: V. Isopoda . In: Maria Dahl, Fritz Peus (Ed.): The animal world of Germany and the adjacent parts of the sea according to their characteristics and their way of life . tape 51 , 1st delivery. VEB Gustav Fischer Verlag, Jena 1965, p. 149 .
- ↑ a b c Rudi Verovnik, Simona Prevorčnik, Jure Jugovic (2009): Description of a neotype for Asellus aquaticus Linne, 1758 (Crustacea: Isopoda: Asellidae), with description of a new subterranean Asellus species from Europe. Zoologischer Anzeiger 248: 101-118. doi : 10.1016 / j.jcz.2009.03.001
- ↑ a b Schmidt-Kloiber A. & Hering D. (editors): www.freshwaterecology.info - the taxa and autecology database for freshwater organisms, version 7.0 (accessed on November 12, 2016) (login required)
- ↑ Frédéric Hervant, J. Mathieu, D. Garin and A. Freminet: Behavioral, ventilatory and metabolic responses of the hypogean Niphargus virei (Crustacea: Amphipoda) and the epigean Asellus aquaticus (Crustacea: Isopoda) to hypoxia and subsequent severe recovery. Physiological Zoology, 69 (6), pp. 1277-1300, 1996
- ↑ Susanne Mommertz: Investigations on the sexual behavior of Asellus aquaticus L. Dissertation of the Faculty of Biology at the Ludwig Maximilians University in Munich, Shaker Verlag , Aachen 1993 ISBN 3-86111-778-9
- ^ Sarah CB Christensen, Erik Arvin, Erling Nissen, Hans-Jørgen Albrechtsen (2013): Asellus aquaticus as a Potential Carrier of Escherichia coli and Other Coliform Bacteria into Drinking Water Distribution Systems. International Journal of Environmental Research and Public Health 10 (3): 845-855. doi : 10.3390 / ijerph10030845
- ↑ "Limit values will certainly be exceeded" Archived copy ( memento of the original from September 16, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ When woodlice carcasses gush out of the tap Archived copy ( memento of the original from August 28, 2009 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Ute Michels, Jessica Polak, Michael Scheideler, Günter Gunkel: Representative sampling of drinking water distribution systems. In: U. Michels, G. Gunkel, M. Scheideler & K. Ripl (editors): Invertebrates in drinking water - sampling, analysis and evaluation. University Press of the Technical University of Berlin, 2013. ISBN 978-3-7983-2575-3
- ↑ Hans Jürgen Hahn & Norbert Klein: Animals in the drinking water distribution, old topic - new perspective. Der Hygieneinspektor 8 (2013), special issue drinking water hygiene: 20-24.
- ↑ Editing: BMBF LS5 Internet editorship: Binnenasseln (Isopoda: Oniscidea & Asellota) - Rote Liste Rote Liste. Retrieved July 1, 2020 .
- ↑ Simona Prevorčnik, Jure Jugovic, Boris Sket (2009): Geography of morphological differentiation in Asellus aquaticus (Crustacea: Isopoda: Asellidae). Journal of Zoological Systematics and Evolutionary Research 47 (2): 124-131. doi : 10.1111 / j.1439-0469.2008.00493.x
- ↑ Dmitry A. Sidorov, Simona Prevorčnik (2016): A review of the genus Asellus EL Geoffroy, 1762 Crustacea: Isopoda: Asellidae) from the Asian part of Russia, with description of plesiomorphic A. turanaicus sp.n. Arthropoda Selecta 25 (2): 157-169.
