Floating shrimp
| Floating shrimp | ||||||||||||
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Hemimysis anomala |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Mysida | ||||||||||||
| Haworth , 1825 |
As mysida (Mysid), also Schwebgarnelen or glass crabs one is order of crustaceans called the world's approximately 1,000 species in the oceans , in brackish water , but also live in fresh water.
Outwardly, the hover shrimp resemble most of the other shrimps that are placed in the order of the decapod shrimp , but are not closely related to them. The mysida belong to the superiority of the peracarida (Peracarida), also to the amphipods (amphipods) and isopods (Isopoda) are counted. It is characteristic of the Peracarida that they carry their young in a breeding bag on the belly side.
features
The animals are usually small and only reach 0.3 to 2.5 centimeters in length. They have a well-developed carapace that covers the entire head and thorax , but is only connected to the first three or four thoracic segments. The long abdomen , which gives the Mysida its shrimp-like appearance, ends in a wide tail fan .
The majority of hover shrimp is glass-like, transparent, but deep-sea species are often red in color. Many species have dark, star-shaped patterns. These are formed by special cell arrangements that allow these floating shrimp to adapt their color to the ground. They can darken if they appear against a dark background or take on an olive-green color if they live on a green algae growth.
Cephalothorax
In the Mysida, the head section is closely connected to the chest section (cephalothorax). The eyes sit on movable stems. Both pairs of antennae are two-branched, as are their striding legs (pereiopods), i. that is, they correspond to the split bone of the arthropod with an inner and an outer branch. In some species a branch can be reduced on the last pair of striding legs. The thoracic segments carry eight pairs of striding legs. The first and sometimes the second pair have scissor-like claws. The base of some female pereiopods is widened. These flap-like, adjoining appendages of the extremities (oostegite) form a breeding space on the abdomen, the marsupium .
abdomen
The abdomen (abdomen) consists of six segments. The first five segments are similar, they carry the five pairs of two- branch swimming legs (pleiopods), which are usually very small and reduced in females. The swimming legs of the males can be modified for various tasks during mating. At the end of the sixth segment, which is twice as long as the others, there is a widened telson . The last segment has a pair on both sides of the telson lying bipartite uropods . The telson and uropods form the tail fan, which plays an important role in the movements of the hover shrimp. In case of danger, they can hit the abdomen with the tail fan forward against the thorax and thus escape very quickly using the recoil principle. In the endopodites (inner branches) of the uropods there are statocysts that function as organs of equilibrium.
distribution
The hover shrimp are found worldwide in all seas and on all continents. Their main habitat is the sea, where they can be found mainly on the coasts near the bottom. Some species dig in the sand or mud, others live pelagic , that is, in the open sea. The species that dig their burrows in the ground only climb the water column at night to look for food. Mysida can also occur in the deep sea in the Abyssal between 5700 and 7200 meters depth. Some specialized species inhabit sea caves.
Hover shrimp can occur in large schools that can reach a length of several kilometers. Such swarms can also be observed in the large freshwater lakes of North America, as well as in European lakes such as Lake Constance . These are representatives of the hover shrimp family Mysidae, such as the relic crayfish, originally from the estuaries of the rivers and the brackish water zones of the seas . These migrate as neozoa , spread with the help of humans, at great speed along the rivers and into the lakes. There they can lead to a shift in the ecological balance.
nutrition
As part of the zooplankton, the Mysida are an important food for fish. As filter feeders, they feed themselves on the smallest organic particles and living beings, some species graze the algae growth on the hard ground or on larger plants. However, some species also feed on zooplankton and use their claws to catch other smaller types of cancer such as B. ostracods (Ostracoda) or mollusks .
Systematics
The Mysida are divided into four families:
- Lepidomysidae Clarke, 1961
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Mysidae Haworth, 1825
- Hemimysis anomala Sars, 1907
- Limnomysis benedeni Czerniavsky, 1882
- Mysis relicta Lovén, 1862
- Petalophthalmidae Czerniavsky, 1882
- Stygiomysidae Caroli , 1937
Neozoa in Europe
Again and again, these shrimp-like crabs are found in Central European rivers and even inland lakes. They often live there in large numbers. It is not yet clear how these neozoa were able to spread into the lakes. Among other things, it is suspected of being carried off by boats.
In the Danube alone there are currently ten freshwater species from the Mysidae family , making the river the world's richest inland waterway in Mysids. The species originally come from the Pontocaspian distribution area, their occurrence was limited to the lower Danube and the Danube Delta, with an affinity for brackish water.
Limnomysis benedeni was the first floating shrimp that was discovered in 1973 for Austria in the Danube lowlands between Vienna and Hainburg . From here it spread upriver over the Main-Danube Canal to the Netherlands and France. It was first discovered in the summer of 2006 in Lake Constance. In 2007 the species occurred in the entire Obersee and formed schools of several million animals. The floating shrimp is one of the fastest spreading neozoa in Lake Constance.
Also Hemimysis anomala was probably spread throughout Europe by shipping. This myside has also been observed in the Danube since 1998. Taken from the Caspian Sea and released in Lithuania , it reached the Rhine via the Baltic Sea and the adjoining shipping canals and from here upriver via the Main and Main-Danube Canal to the Upper Danube. Hemimysis anomala populated large parts of the Rhine. In Geneva this opossum was found in December 2007 for the first time. Since the end of 2006, this Pontocaspic species has also immigrated to the United States ( Muskegon- Lake in Michigan ) and Canada ( Lake Ontario ).
In 2005, divers in the Horseshoe Lake in Halle in Saxony-Anhalt also discovered the swarming floating shrimp Hemimysis anomala . It was then found for the first time in an inland lake in Central Germany and registered by biologists from the Martin Luther University in Halle-Wittenberg. It can be assumed that as alien animals they have a predominantly negative influence on native fish species (e.g. whitefish ), whose young they eat plankton food without being sufficiently recognized as food themselves (Steinmann lc ).
Individual evidence
- ↑ P. Steinmann: Schwebegarnelen als Neozoen
- ↑ Press release from Martin Luther University Halle-Wittenberg
