Palaemon varians
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| Leach , 1814 |
Palaemon varians , also known in German as swimming shrimp , brackish water shrimp or glass shrimp , is a species of shrimp from the genus of rock shrimp ( Palaemon ) within the family of rock and partner shrimp (Palaemonidae). It wasknownunder the synonym Palaemonetes varians until a taxonomic revision in 2013, this name isstill widespread,especially in applied areas such as aquaristics .
features
The swimming shrimp reaches a maximum length of 50 mm, but often remains smaller (approx. 40 mm). It is colorless and translucent without any noticeable coloring or drawing. On the carapace , below the orbital pit (the indentation of the edge of the carapace to accommodate the eyes), there are two thorns, called the antennular and branchiostegal thorns. The rostrum (the thorn-like extension that extends the carapace forwards, between the eyes) can be curved or straight, it has four to six teeth on the upper side (dorsal side) and two teeth on the lower side (ventral side). The first antennae have three antennae flagella. The shorter branch of the outer flagellum reaches about four fifths of the length of the antenna base (pedunculus), about three quarters of its length is fused with the longer branch. The mandibles have a palpus .
While animals from the Atlantic , North and Baltic Seas can be identified according to these characteristics, other characteristics must be taken into account in order to distinguish between animals from the Mediterranean region . An identification key can be found in Tzomos & Athanasios Koukouras (2015).
Occurrence
The swimming shrimp occurs throughout Europe in coastal areas and in brackish water areas. Occurrences exist from Norway in the north, along the Atlantic coast, south to Spain , including Great Britain and on the coasts of the Mediterranean Sea, to the east on the south side to Tunisia and on the north coast to the Camargue .
The population density in brackish water areas (e.g. estuaries or the bottom of the Baltic Sea) seems to be significantly higher than in the sea itself. Overall, the shrimp is extremely adaptable with regard to the salt content in the water. The natural life expectancy is given as 1.5 to 2 years.
Way of life
According to its occurrence, the swimming shrimp has a wide temperature tolerance between 4 and 22 ° C. The animals live socially, even smaller animals are not attacked by adult shrimp.
Aquaristics
The swimming shrimp should be kept in a brackish water aquarium. Aquariums from 30 liters are sufficient, but you have to consider that these shrimps are quite lively and need a lot of swimming space. The pool should also be covered, as the shrimp will jump out of the pool quickly if they are frightened. The animals tolerate a mean salt content of 15 ppt (1.5%). With such a salt content, the females also set eggs and the development of the larvae can be observed if the water values are good. Snails and hermit crabs , which can also cope with lower salt concentrations, are suitable for socialization .
Phylogeny, taxonomy, systematics
The genus Palaemon (according to today's view) comprises a good 80 species and is distributed almost worldwide. Until 2013, all species with a palpus (button) on the mandibles were regarded as the genus Palaemonetes , those without palpus as the genus Palaemon , whereby Palaemon species in the old sense are more marine, Palaemonetes species are limnic (in fresh water) or in brackish water. In 2012 an English research group was able to show by means of phylogenomic analyzes that these “genera” are not natural units ( paraphyletic ); rather, the types of different geographical regions are more closely related to one another, regardless of the previous genus allocation. Morphological investigations had already pointed in the same direction beforehand. In 2013, the previous genera were therefore synonymous and this view quickly gained acceptance. The species must therefore bear the name Palaemon varians , as it did when it was first described .
If one only considers the European region, excluding more distant areas, the West Atlantic and Mediterranean species of the former genus Palaemonetes , including Palaemon varians , are still closely related to one another and form a common clade . All other species, with the exception of Palaemon varians themselves, are distributed exclusively in the Mediterranean region. However, the East Asian species Palaemon macrodactylus , which also colonizes brackish water habitats, was introduced to England as a neozoon and may possibly spread further.
etymology
The generic name Palaemon goes back to the Greek sea and port deity Palaimon ( Latinized : Palaemon ). The species name varians comes from the Latin verb variare (German: alternate, change).
literature
- Werner DeHaas, Fredy Knorr: What lives in the sea on Europe's coasts? Mediterranean, Atlantic, North Sea, Baltic Sea. Special edition. Müller-Rüschlikon, Cham 1999, ISBN 3-27-501302-5 .
Individual evidence
- ↑ a b c Christopher W. Ashelby, Tim M. Worsfold, Charles HJM Fransen: First records of the oriental prawn Palaemon macrodactylus (Decapoda: Caridea), an alien species in European waters, with a revised key to British Palaemonidae. In: Journal of the Marine Biological Association of the United Kingdom. Vol. 84, No. 5, 2004, ISSN 0025-3154 , pp. 1041-1050, doi : 10.1017 / S0025315404010392h .
- ^ Peter J. Hayward, John S. Ryland (Eds.): Handbook of the Marine Fauna of North-West Europe. Oxford University Press, Oxford et al. 1995, ISBN 0-19-854055-8 , description on p. 412.
- ↑ a b c Theodoros Tzomos, Athanasios Koukouras: Redescription of Palaemon antennarius H. Milne Edwards, 1837 and Palaemon migratorius (Heller, 1862) (Crustacea, Decapoda, Palaemonidae) and description of two new species of the genus from the circum-Mediterranean area . In: Zootaxa . Vol. 3905, No. 1, 2015, pp. 27-51, doi : 10.11646 / zootaxa.3905.1.2 .
- ↑ Dag Dolmen: Palaemonetes varians (LEACH) (Crustacea, Decapoda, Natantia), in Norway. In: Sarsia. Vol. 82, No. 1, 1997, ISSN 0036-4827 , pp. 19-21.
- ↑ Christopher W. Ashelby, Timothy J. Page, Sammy de Grave, Jane M. Hughes, Magnus L. Johnson: Regional scale speciation reveals multiple invasions of freshwater in Palaemoninae (Decapoda). In: Zoologica Scripta. Vol. 41, No. 3, 2012, ISSN 0300-3256 , pp. 293-306, doi : 10.1111 / j.1463-6409.2012.00535.x .
- ↑ Sammy de Grave, Christopher W. Ashelby: A re-appraisal of the systematic status of selected genera in Palaemoninae (Crustacea: Decapoda: Palaemonidae). In: Zootaxa. Vol. 3734, No. 3, 2013, pp. 331-344, doi : 10.11646 / zootaxa.3734.3.3 .
- ↑ Palaemon varians at WoRMS World Register of Marine Species , accessed January 20, 2016.
- ↑ José A. Cuesta, Pilar Drake, Gonzalo Martínez-Rodríguez, Antonio Rodríguez, Christoph D. Schubart: Molecular phylogeny of the genera Palaemon and Palaemonetes (Decapoda, Caridea, Palaemonidae) from a European perspective. In: Crustaceana. Vol. 85, No. 7, 2012, ISSN 0011-216X , pp. 877-888, doi : 10.1163 / 156854012X650197 .
Web links
- Palaemonetes varians - Atlantic ditch shrimp (English) on the website sealifebase.org