Craspedacusta

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Craspedacusta
Craspedacusta sowerbii

Craspedacusta sowerbii

Systematics
Trunk : Cnidarians (Cnidaria)
Class : Hydrozoa (Hydrozoa)
Subclass : Trachylinae
Order : Limnomedusae
Family : Olindiidae
Genre : Craspedacusta
Scientific name
Craspedacusta
Lankester , 1880

Craspedacusta is a genus of freshwater hydrozoa with a distribution center in the Yangtze River Valley, China. One species, the freshwater jellyfish Craspedacusta sowerbii , was transported from there around the world and is now distributed as a neozoon in Central Europe.

features

As far as is known, the species of the genus undergo a regular generation change ( metagenesis ) between a polyp and a medusa or jellyfish stage . In addition, there are two other asexual stages.

Medusa

Medusas reach an umbrella diameter of up to 25 millimeters, but immediately after the polyp is released ( strobilation ), they are only 0.7 to 1 millimeter in size. The umbrella is almost hemispherical, a little less high than it is wide and relatively thick. It is traversed by four cross-shaped unbranched radial channels, which open into an annular channel surrounding the edge of the screen. The stomach space behind the four-lobed manubrium begins as a uniform, square pocket that narrows conically towards the top and splits in a cross shape towards the edge into four chambers, at the tips of which the radial canals branch off. The simple, bag-shaped gonads sit on the radial canals, they are pale green or yellow-brown in color. At the edge of the screen there are numerous (from about 100 to more than 500) tentacles at the same distance and of uniform structure, but sometimes of different sizes. The edge of the umbrella is slightly wavy, in each of the bays there is a statocyst in radially arranged blind-ended short channels . Medusa are separate sexes. After fertilization , the female animals develop planula larvae, which attach to the bottom of the water and establish a new generation of polyps.

In Europe, the freshwater jellyfish Craspedacusta sowerbii is the only medusa found in freshwater and is therefore unmistakable.

polyp

The polyp stage sits individually (solitary) or forms small, creeping colonies of two to four. rarely up to seven hydroid polyps that result from sprouting (asexual reproduction). The polyps are cylindrical in shape and have no tentacles. Around the mouth there are warty protrusions (cnidocysts) in which the nettle cells lie; these form a hemispherical head, under which the polyp body is constricted in the shape of a narrow neck. The Medusa buds sit laterally in the middle or lower part of the body. The polyps can form crawling larvae asexually called frustula as well as resistant podocysts that act as permanent stages ; these also resist dehydration. Polyps reach about 0.5 to 2 millimeters in length.

The polyp stage is present in the water for much longer periods of time, but is usually overlooked because of its inconspicuousness.

Biology and way of life

Biological data are almost exclusively available for Craspedacusta sowerbii . As far as data are available on the other species from Chinese waters, these colonize comparable waters and can occur side by side (sympatric) in the same water body. They colonize stagnant water, from small ponds to lakes. There are many reports of finding basins and artificial bodies of water from Europe. The medusas feed them predatory, preferring the juvenile stages of planktonic copepods ( copepods ) as prey. Their density and their ecological impact usually remain low, but under special circumstances they can become so common that they influence the nutrient cycle of the water body. Due to the very high water content of over 99 percent (marine jellyfish are isotonic with seawater and can therefore only achieve slightly lower water contents), their biomass and production remain low.Mesotrophic to eutrophic , relatively warm waters are preferred to be colonized . The formation of the medusa is also temperature-dependent and usually only takes place in warm water.

species

Although up to 15 species or subspecies have been described in the genus (many of them, however, originally as varieties or subspecies), almost all of the authors assume that most of these names are synonyms . The number and delimitation of the species are still unclear, most of the investigators today assume three to four valid species.The shape of the statocysts, which is often used to diagnose species, and the color of the gonads, like many other characteristics, seem to be so variable within the species that Species differences on this basis are doubtful.

  • Craspedacusta sowerbii ( freshwater jellyfish ) . The most common species of the genus and, due to displacement, the only cosmopolitan freshwater jellyfish today. Contrary to previous assumptions, an origin from China is now considered certain.
  • Craspedacusta kiatingi . According to molecular data, sister species of C. sowerbii and genetically very similar, so that it has been synonymous with this one by many researchers. Known from waters in the Yangtze River valley, China, an occurrence near Beijing is attributed to human displacement.
  • Craspedacusta sinensis . Known mainly from waters in the Yangtze River valley, China, relatively widespread and common here.
  • Craspedacusta iseana . This species was discovered in a well in Tsu City, Mie Prefecture, Japanin 1922and has not been found since then. Since the original site was destroyed soon after it was discovered, the species is believed to have become extinct. However, the independence of the species is not assured; it can no longer be investigated using molecular methods because the type material has disappeared.

Phylogenomic studies (studies of the relationships based on the comparison of homologous DNA sequences) of European freshwater medusa have further complicated the picture. Data from German individuals were genetically quite uniform, which would indicate a single species, but some individuals in their sequence corresponded more closely to those that had been assigned to Craspedacusta kiatingi in China . Individuals discovered in Greece only in 2015 show a very different sequence, which is, however, closely related to a Chinese individual from the province of Hubei on the Yangtze River; however, this was also assigned to Craspedacusta sowerbii . It can therefore be assumed that there were several import events in Europe. It is unclear whether different species actually live here, contrary to all previous assumptions.

Individual evidence

  1. ^ A b Jean Bouillon & Ferdinando Boero (2000): Synopsis of the families and genera of the hydromedusae of the world, with a list of the worldwide species. Thalassia Salentina 24. doi : 10.1285 / i15910725v24p47
  2. ↑ a b Thomas Jankowski (2001): The freshwater medusae of the world - a taxonomic and systematic literature study with some remarks on other inland water jellyfish. Hydrobiologia 462: 91-113.
  3. ^ A b Cheryl Lewis, Masao Migita, Hiroshi Hashimoto, Allen G. Collins (2012): On the occurrence of freshwater jellyfish in Japan 1928–2011: eighty-three years of records of mamizu kurage (Limnomedusae, Olindiidae). Proceedings of the Biological Society of Washington 125 (2): 165-179.
  4. ↑ a b c Li Q.Zhang, Gui T.Wang, WeiJ.Yao, Wen X.Li, Qian Gao (2009): Molecular systematics of medusae in the genus Craspedacusta (Cnidaria: Hydrozoa: Limnomedusae) in China with the reference to the identity of species. Journal of Plankton Research 31 (5): 563-570. doi : 10.1093 / plankt / fbp005
  5. ↑ Thomas Jankowski, Tido Strauss, Hans Toni Ratte (2005): Trophic interactions of the freshwater jellyfish Craspedacusta sowerbii. Journal of Plankton Research 27 (8): 811-823.
  6. ^ Herbert W. Ludwig (1977): 99.26 per cent Water Content in the Freshwater Medusa Craspedacusta sowerbii. Journal of Natural Research Section C 32 (11-12): 1011-1012.
  7. ↑ Thomas Jankowski (2003): Chemical composition and biomass parameters of a population of Craspedacusta sowerbii Lank1880 (Cnidaria: Limnomedusa). Journal of Plankton Research 22 (7): 1329-1340.
  8. ↑ a b Schuchert, P. (2015). Craspedacusta Lankester, 1880. In: Schuchert, P. (2015) World Hydrozoa database. Accessed by Schuchert, P. (2015) World Hydrozoa database, on August 4, 2015
  9. ↑ Thomas Jankowski, Allen G. Collins, Richard Campbell (2008): Global diversity of inland water cnidarians. Hydrobiologia 595: 35-40. doi : 10.1007 / S10750-007-9001-9
  10. ↑ Gisela B. Fritz, Martin Pfannkuchen, Andy Reuner, Ralph O. Schill, Franz Brümmer (2009): Craspedacusta sowerbii, Lankester 1880 - population dispersal analysis using COI and ITS sequences. Journal of Limnology 68 (1): 46-52.
  11. ↑ Ioannis Karaouzas, Stamatis Zogaris, Manuel Lopes-Lima. Elsa Froufe, Simone Varandas, Amılcar Teixeira, Ronaldo Sousa (2015): First record of the freshwater jellyfish Craspedacusta sowerbii Lankester, 1880 in Greece suggests distinct European invasion events. Limnology doi : 10.1007 / s10201-015-0452-9 (online before print)