Mysida

Hemimysis anomala

As floating shrimp ( Mysida ), also Schwebgarnelen or glass crabs is an order of crustaceans called, with about 1000 species live in the seas, in brackish water, but also in freshwater worldwide.

The floating shrimp outwardly resemble most other shrimp that are placed in the order of decapods, but are not closely related to them. The floating shrimp belong to the superiority of the knapsack crabs ( Peracarida ), which also includes the amphipods ( Amphipoda ) and isopods ( Isopoda ) are counted. It is characteristic of the Perakarida that they deliver their young in a brood pouch on the abdomen side lying.

Features

The animals are usually small and reach only 0.3 to 2.5 centimeters in length. They have a well-developed carapace, which covers the entire head and thorax, but is only connected to the first three or four Thorakalsegmenten. The long abdomen, which gives the Mysida the shrimp-like appearance, ending in a broad tail fan.

The majority of floating shrimp is glassy transparent, deep-sea species, however, are often colored red. Many species have dark, star-shaped pattern. These are formed by specific cell arrangements that provide these shrimp floating the possibility to adapt its color to the ground. You can darken when they occur against a dark background or accept an olive green color, if they live on a green algae.

Cephalothorax

The head section is closely connected with the Mysida with the breast section ( cephalothorax ). The eyes are on movable stalks. Both pairs of antennae are biramose, as their walking legs ( pereiopods ), ie they correspond to the gap leg of arthropods with an inner and an outer branch. In some species the last couple walking legs may be reduced one branch. The Thorakalsegmente carry eight pairs of walking legs. The first and sometimes the second pair has scissor-like claws. The basis of some pereiopods of female is widened. These lobe-like, adjoining annexes to the extremities ( Oostegite ) form a ventral side lying brood chamber, the marsupium.

Abdomen

The abdomen (abdomen) consists of six segments. The first five segments are similar, they carry the five bifurcated swimming leg pairs ( Pleiopoden ), which usually are very small and reduced in females. In the males, the Schwimmebeine can be modified for different tasks during copulation. At the end of the sixth segment, which is twice as long as the other is, there is a broadened Telson. The last segment has a pair on either side of the telson lying bipartite uropods. Telson and uropods form the tail fan, which plays an important role in the movements of the floating shrimp. In case of danger they can beat the abdomen with the tail fan forward against the thorax and thereby escape very quickly after the reaction principle. In the endopodite ( inner branches ) of the uropods are statocysts, which act as organs of equilibrium.

Dissemination

The floating shrimp are common in all seas and on all continents around the world. Their main habitat is the sea, where they can be found mainly on the coasts near the ground. Some species burrow in the sand or mud, others live pelagic, ie in the open sea. The species that dig their burrows in the ground, only to rise up the water column at night to search for food. Mysida may also occur in the deep sea in the Abyssal 5700-7200 meters depth. Some specialized species inhabiting marine caves.

Floating shrimp can occur in large flocks, which reach a length of several kilometers. Even in the large freshwater lakes of North America, as well as in European lakes as Lake Constance, these swarms are observed. It involves originally native to the estuaries of the rivers and brackish water zones of the oceans representatives of floating shrimp family Mysidae as the Reliktkrebschen. These migrate as invasive species, distributed through the instrumentality of man, with great speed along the rivers and in the lakes a. There, they can lead to a shift in the ecological balance.

Nutrition

The Mysida are an important food fish as part of the zooplankton. They feed on itself as filter feeders of the smallest organic particles and living organisms, some species graze the algae on the hard floor or on larger plants from. However, some species also feed on zooplankton and start using their scissors other smaller cancers such as ostracods ( Ostracoda ) or mollusks.

System

The Mysida be divided into four families:

• Lepidomysidae Clarke, 1961
• Mysidae Haworth, 1825 Hemimysis anomala Sars, 1907
• Limnomysis benedeni Czerniavsky, 1882
• Mysis relicta Lovén, 1862

Invasive species in Europe

Again and again finds of this shrimp-like crustaceans in central European rivers and even lakes are made. They live often in large numbers. The ways in which these invasive species could spread to the lakes, is not yet clear. Among other things, a carryover is suspected by boats.

In the Danube alone currently occur ten freshwater species from the family of Mysidae, the river, making it the richest in Mysiden inland waters of the earth. The species originally from the Ponto- Caspian area of ​​distribution, its occurrence was to brackish water, limited to the lower Danube and the Danube Delta, with affinity.

Limnomysis benedeni was the first opossum, which was discovered in 1973 in Austria for the Danube valley between Vienna and Hainburg. From there it has spread upstream along the Main -Danube Canal to the Netherlands and France. It was first detected in the summer of 2006 in Lake Constance. In 2007 the type was found throughout the upper lake and formed swarms of millions of animals. The opossum is thus one of the most rapidly spreading invasive species in Lake Constance.

Hemimysis anomala was also probably spread across Europe by shipping. Since 1998 this Myside is also observed in the Danube. Taken from the Caspian Sea and suspended in Lithuania, she came across the Baltic Sea and the adjacent navigation channels here in the Rhine and from there up the river on Main and Main -Danube Canal in the upper Danube. Hemimysis anomala has colonized large parts of the Rhine and could be bedeni also soon introduced from here by shipping as Limnomysis in Lake Constance. In Geneva this opossum was found for the first time in December 2007. Since late 2006, this pontokaspische Art ( Muskegon Lake in Michigan ) and Canada ( Ontario ) immigrated to the United States.

In 2005, divers discovered in the Horseshoe in Saxony-Anhalt Halle also the swarm-forming opossum Hemimysis anomala. At that time it was found for the first time in a mid- lake in Germany and registered by biologists at the Martin -Luther- University Halle- Wittenberg. It is likely that these " Schwebgarnelen " as biotope strange animals to humans mainly negative influence (eg ) on native fish species (eg whitefish ) have, their children eat up to plankton food without having to be self hinlangend recognized or used as food can ( Steinmann lc ).