Sea walnut

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Sea walnut
Mnemiopsis Leidyi in the “New England Aquarium” in Boston

Mnemiopsis Leidyi in the “New England Aquarium” in Boston

Systematics
Trunk : Rib jellyfish (Ctenophora)
Class : Tentaculata
Order : Lobata
Family : Bolinopsidae
Genre : Mnemiopsis
Type : Sea walnut
Scientific name
Mnemiopsis Leidyi
( Agassiz , 1865)

Mnemiopsis Leidyi , German sea ​​walnut , is a species of the rib jellyfish (Ctenophora) from the order of the Lobata . It feeds on zooplankton , fish larvae and eggs.

description

Mnemiopsis Leidyi is transparent, hyaline , usually a little milky. When fully grown, it reaches a body length of around 100 to 110 millimeters. When viewed from above, the body is flattened in the plane of the tentacle. The body surface is smooth, often with numerous, wart-like protrusions. When viewed from the side, the body is elliptical in outline, seen from the narrow side, and rounded to almost pear-shaped from the broad side. The upper body pole (opposite the mouth opening, aboral) is rounded, not pointed as in the very similar and probably closely related genus Bolinopsis . In a spread-out side view, various attachments can be seen on the underside (oral) of the body: two very large, laterally seated mouth lobes and four shorter appendages surrounding the mouth opening, which are called auricles. The flat mouth lobes reach about two fifths of the body length, they are slightly wider than long, they arise already near the front end of the body, extend laterally of the body, protruding from it and are broadly rounded at the end. In the angles between the mouth lobe and the body, recessed longitudinal furrows are formed, which are typical of the genus. When at rest, the mouth lobes overlap. The flattened, triangular auricles reach about a quarter of the length of the body, they support food intake like fingers. Sitting at the side of the mouth opening, two tentacle pockets, the tentacles in them are quite short in the adult animal and probably rudimentary and functionless. They are not, as in other comb jellyfish, retractable. In addition, the slit-like mouth is surrounded by a series of short, simply built tentacles.

The eight rows of plate-shaped eyelash plates enable the animal to move (the wide mouth lobes are not involved in the movement). On living animals they are shimmering in color due to the refraction of light. As is typical of the Lobata order, they consist of four longer and four shorter rows. At the distal (aboral) end of the organism, the apical sense organ with the statocyst sits in a depression .

The larvae have an egg-shaped body. The two tentacles are, unlike the adult animals, long and conspicuous, they sit in two easily recognizable tentacle pockets. The eight rows of eyelash platelets are almost the same length, they do not reach the mouth opening. The characteristic mouth lobes begin to develop from a body length of about 5 millimeters.

Bioluminescence

Individuals of the species, like most comb jellyfish, can produce blue-green light in the dark by bioluminescence . Only on the dark-adapted animal can be seen eight luminous lines that trace the body contour. The luminescence is stimulated by touching the eyelash platelets, which act as mechanoreceptors. Light is produced in the photocytes, light-producing cells that are located on the outside of the eight radial channels running through the interior of the animal, between the ciliate cells of the oar plates and the wall cells of the channels. As is typical for photocytes, the endoplasmic reticulum is particularly strong. The light-emitting protein, or photoprotein, is mnemiopsin, a member of the coelenterazines that are typical of jellyfish and cnidarians. Contrary to previous assumptions, it has been shown that Mnemiopsis synthesizes the protein itself and does not ingest it with prey organisms.

distribution

The species was originally distributed in subtropical waters on the Atlantic coast of North and South America. In 1982 specimens were first sighted in the Black Sea . Presumably they got there through ballast water from cargo ships. Due to a lack of enemies, the species spread quickly, displacing native species. Yields from the anchovy fishery fell to a tenth of what it was before the species invaded. The species reached its maximum population density in the Black Sea in 1989 with over 300 specimens per cubic meter of water. Only the introduction of the comb jelly Beroe ovata , a predator, was able to push back the population. Presumably through the ballast water of ships, Mnemiopsis Leidyi was also able to penetrate into the Caspian Sea . On October 17, 2006, researchers from the Leibniz Institute for Marine Sciences discovered the species in the Baltic Sea . A density of 30 specimens per cubic meter of water was found. The population rose sharply here too, reaching 92 specimens per cubic meter. The species reproduces best at water temperatures between 24 and 28 ° C, but can reproduce from 12 ° C. On the American Atlantic coast, it is distributed north to Narragansett Bay . In the Baltic Sea and North Sea they can overwinter at water temperatures of up to 4 ° C. Warmer winters could therefore make the populations grow even faster. Overall, jellyfish appear more and more frequently in the North Sea - including predators of the Mnemiopsis Leidyi: the glass lobed jellyfish Bolinopsis infundibulum and, as in the Black Sea, the melon jellyfish of the genus Beroe . Researchers at the Helmholtz Association belonging Biological Institute Helgoland (BAH) hinted in this regard that the predators the Mnemiopsis at least - as in the Black Sea could keep them at bay - happen.

Taxonomy

Three species are described in the genus Mnemiopsis . Mnemiopsis mccradyi Mayer, 1900 is said to differ from M.leidyi by its more warty body . This species was specified on the American Atlantic coast south of Cape Hatteras , but is now mostly synonymous with M.leidyi . The type species of the genus, Mnemiopsis gardeni L. Agassiz, 1860, is possibly synonymous, so that the genus would be monotypical . However, this would raise nomenclature problems because, according to the rules of zoological nomenclature, this would then be the valid name of the species, so that the species name Mnemiopsis Leidyi , used in hundreds of articles, would become a synonym.

Mnemiopsis is the genera Bolinopsis and Leseuria the family Bolinopsidae Bigelow, 1912. However, it was in 2015, according to genetic data, drawn the monophyly of this family in doubt.

Web links

Commons : Sea walnut  album with pictures, videos and audio files

Individual evidence

  1. ^ A b Alfred Goldsborough Mayer (1912): Ctenophores of the Atlantic Coast of North America. Carnegie Institution of Washington Publication no.162.Mnemiopsis Leidyi on page 26 ff.
  2. ^ Otto MP Oliveira & Alvaro E. Migotto (2006): Pelagic ctenophores from the São Sebastião Channel, southeastern Brazil. Zootaxa 1183: 1-26.
  3. ^ RA Moore (1924): Luminescence in Mnemiopsis. Journal of General Physiology 6 (4): 403-412.
  4. ↑ MR Aghamaali, V. Jafarian, S. Sariri, M. Molakarimi, B. Rasti, M. Taghdir, RH Sajedi, S. Hosseinkhani (2011): Cloning, sequencing, expression and structural investigation of mnemiopsin from Mnemiopsis Leidyi: an attempt toward understanding Ca2 + -regulated photoproteins. Protein Journal 30 (8): 566-574. doi : 10.1007 / s10930-011-9363-8
  5. ↑ TA Shiganova (1998): Invasion of the Black Sea by the ctenophore Mnemiopsis leidyi and recent changes in pelagic community structure. Fisheries Oceanography 7: 305-310. doi : 10.1046 / j.1365-2419.1998.00080.x
  6. ↑ Tamara A. Shiganova & Yulia V. Bulgakova (2000): Effects of gelatinous plankton on Black Sea and Sea of ​​Azov fish and their food resources. ICES Journal of Marine Science 57: 641-648. doi : 10.1006 / jmsc.2000.0736
  7. ↑ T. Shiganova Z. Mirzoyan E. Studenikina S. Volovik I. Siokou-Frangou S. Zervoudaki E. Christou A. Skirta H. Dumont (2001): Population development of the invader ctenophore Mnemiopsis Leidyi in the Black Sea and in other seas of the Mediterranean basin. Marine Biology 139 (3): 431-445. doi : 10.1007 / s002270100554
  8. ↑ Vladimir P. Ivanov, Andrey M. Kamakin, Vladimir B. Ushivtzev, Tamara Shiganova, Olga Zhukova, Nikolay Aladin, Susan I. Wilson, G. Richard Harbison, Henri J. Dumont (2000): Invasion of the Caspian Sea by the comb jellyfish Mnemiopsis Leidyi (Ctenophora). Biological Invasions 2: 255-258.
  9. ↑ Jamileh Javidpour, Ulrich Sommer , Tamara Shiganova (2006): First record of Mnemiopsis leidyi A. Agassiz, 1865 in the Baltic Sea. Aquatic Invasions 1 (4): 299-302. doi : 10.3391 / ai.2006.1.4.17
  10. ↑ Sandra Kube, Lutz Postel, Christopher Honnef, Christina B. Augustin (2007): Mnemiopsis Leidyi in the Baltic Sea - distribution and overwintering between autumn 2006 and spring 2007. Aquatic Invasions 2 (2): 137-145.
  11. ↑ Maarten Boersma, Arne M. Malzahn, Wulf Greve, Jamileh Javidpour (2007): The first occurrence of the ctenophore Mnemiopsis Leidyi in the North Sea. Helgoland Marine Research 61: 55. doi : 10.1007 / s10152-006-0055-2
  12. ↑ Jennifer E. Purcell, Tamara A. Shiganova, Mary Beth Decker, Edward D. Houde (2001): The ctenophore Mnemiopsis in native and exotic habitats: US estuaries versus the Black Sea basin. Hydrobiologia 451: 145-176.
  13. ↑ Mills, C. (2011). Mnemiopsis L. Agassiz, 1860. WoRMS World Register of Marine Species. Retrieved April 21, 2017
  14. ↑ Phylum Ctenophora: list of all valid species names, by Claudia E. Mills , accessed April 21, 2017
  15. ↑ Paul Simion, Nicolas Bekkouche, Muriel Jager, Eric Quéinnec, Michaël Manuel (2014): Exploring the potential of small RNA subunit and ITS sequences for resolving phylogenetic relationships within the phylum Ctenophora. Zoology (Jena) 118 (2): 102-114. doi : 10.1016 / j.zool.2014.06.004