Lobata
| Lobata | ||||||||||||
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Bathocyroe fosteri |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Lobata | ||||||||||||
| Eschscholtz , 1825 |
The Lobata are a biologically significant order of rib jellyfish (Ctenophora) from the class Tentaculata . They are characterized by their muscular mouth flaps, which are used to catch prey instead of the tentacles that are preferred in other comb jellyfish.
construction
The body shape of the up to 25 centimeters large lobata is described by three mutually perpendicular axes, the longitudinal axis of the body between the mouth and the organ of equilibrium, the tentacular axis as the connecting axis of the two tentacle sheaths and the pharyngeal axis perpendicular to it. The tentacular axis is shorter than the pharyngeal axis, resulting in an oval cross-section.
Two large muscular mouth lobes flank the stem-shaped protruding mouth and the two tentacles on the side of the mouth , which are distinctly different depending on the species and are even completely absent in the genus Ocyropsis . In this way, an umbrella-like cavity is created between the side of the mouth and the two mouth lobes, as can also be found in the unrelated jellyfish of the cnidarians .
At the two sheaths tentacle two elongated indentations arise in the body wall, the auricular furrows , each go-out over the screen bottom outward to an oral lobes and with long fibers, the Tentillen are occupied. These carry numerous adhesive bodies ( colloblasts ) that are used to catch prey.
As with all rib jellyfish , the comb ribs, which originate from the statocyst , the organ of equilibrium, at the end remote from the mouth can be divided into two groups: two of them run parallel into the two mouth lobes to the left and right of the mouth; the other four run perpendicular to it approximately in the plane of the tentacles and continue on the mouth side in four conical body appendages, the auricles , which, however, have long flagella instead of comb plates . A peculiarity of the Lobata is that on all ridges between the individual platelets there is a furrow with flagella, which presumably transmits the beat signal of the statocyst in a mechanical way. Damage to the comb ribs can also be repaired relatively quickly. The latter could have been the decisive reason for the development of this innovation for the Lobata, who rely on active locomotion.
The light emanating from the central gastric channel system consists of two para gastric channels, which run on both sides along throat to the mouth end, and four current to the mouth end facing away outwardly Transversalkanälen . These divide in a Y-shape and continue in the meridional canals that run below the ridge ribs to the end of the mouth and also cross the mouth lobes in two loop systems. They unite with the ends of the paragastric canals in a circumoral ring canal that is located around the mouth.
distribution and habitat
Lobata species form an important part of the marine plankton and are found in all marine waters around the world. They all live pelagic , i.e. in open water.
Getting around and eating
Lobata swim mouth-side first; although they use their comb ribs to support this, the propulsion comes about mainly through undulating movements of their muscular mouth lobes and auricles.
The flagella that sit on the four auricles create a current of water through which prey such as fish larvae, small crabs and other zooplankton are conducted around them over the outstretched tentils of the auricular ligaments, where they stick to the touch-activated colloblasts and are then transported to the mouth .
The auricles not only generate the flow of food directed to the mouth, but are apparently also capable of perceiving prey in the vicinity and can accordingly actively control the direction of flow of the water - Lobata rib jellyfish thus show a larger behavioral repertoire than was possible until the end of the twentieth century would have thought possible.
The system of mouth lobes and auricles used to catch prey can be viewed as an alternative to tentacles: In contrast to these, it enables the uninterrupted ingestion of food from prey from the micro- and mesozooplankton that are passively floating in the water or only slowly swimming . In contrast to the second larger group of comb jellyfish, the Cydippida , which always first retract their tentacles in a process known as "spin capture" and turn their body to bring them to the end of their mouth, they are therefore more specialized in smaller prey. As a result, they hardly enter into food competition with the Cydippida, but can coexist with them through their alternative strategy. Some scientists consider this to be a selective advantage that favored the phylogenetic development of the Lobata from Cydippida-like ancestors.
Reproduction
Lobata reproduce sexually only. Most are hermaphrodites , so they have both male and female gonads ; Self-fertilization, however, probably only plays a major role in the species of the genus Mnemiopsis . Often the male and then the female germ cells are first released into the water, where fertilization takes place. Further development takes place via a Cydippea stage, which looks like a miniature version of a Cydippida comb jelly, but does not yet have a mouth lobe. Since the young animals do not differ significantly from the adults in terms of their habitat or appearance, one usually does not speak of a larva , so the development is direct.
In the species of the genus Ocyropsis , in contrast to all other comb jellyfish , the sexual organs always appear separately, so male and female individuals can be distinguished.
A remarkable phenomenon that occurs in some Lobata species is what is known as dissogeny : some juveniles reach sexual maturity prematurely and start producing germ cells ; In the course of further development, however, their gonads regress, only to return in the adult phase.
Influence of Lobata in Alien Ecosystems
In 1982, the Lobata species Mnemiopsis Leidyi was observed for the first time in the Black Sea , which was previously not populated by comb jellyfish , where it was presumably reached with the ballast water of ships that had previously crossed the waters of the north-western Atlantic . Without any natural enemies, the population exploded a few years later and not only destroyed numerous fish eggs and larvae, but also successfully displaced all food competitors for the plankton stocks within just ten years, so that the anchovy fishery in particular collapsed completely. The advantages of Mnemiopsis Leidyi apparently consisted not only in being able to exterminate its competitors in the egg or larval stage, but also in the earlier start of feeding, so that the existing zooplankton was already considerably reduced in terms of quantity and species when the remaining fish larvae finally matured into adult animals.
Only with the additional appearance of another comb jellyfish, Beroe ovata , which specialized in Mnemiopsis Leidyi as prey , in 1997 did the ecosystem regain its equilibrium ; however, since then the Black Sea has been populated with two alien species. A similar phenomenon can be observed at the beginning of the 21st century in the Caspian Sea , where Mnemiopsis Leidyi probably ended up in the ballast water of ships sailing the Volga-Don Canal in 1998 or 1999.
In the meantime, it has also been carried off to the western Baltic Sea, as is shown by finds in October 2006 in the Kiel Fjord.
Tribal history
Fossils that can be assigned to the Lobata are not known to this day, so that the phylogenetic relationships must be deduced solely from a comparison with other modern comb jellyfish. A preliminary molecular genetic study showed that a group from the Lobata together with the Cestida and Thalassocalycida forms a monophyletic taxon , i.e. includes all descendants of the last common ancestor of these animals. Morphological peculiarities of the Ganeshida , an order that was not included in the aforementioned study, suggest that this taxon may also belong to the same family.
Systematics
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It is not yet clear whether the Lobata itself is a monophyletic taxon ; it is possible that some Lobata species are more closely related to comb jellyfish of the order Thalassocalycida than to other Lobata species. In this case the taxon Lobata would be paraphyletic , so it did not include all descendants of the parent species.
The following list (as of April 25, 2017) names the currently valid families, genera and species of Lobata according to the list by Claudia E. Mills (University of Washington, USA).
Order Lobata Eschscholtz , 1825
- Bathocyroidae family Harbison and Madin , 1982
- Genus Bathocyroe Madin and Harbison , 1978
- Bathocyroe fosteri Madin and Harbison , 1978
- Bathocyroe longigula Horita, Akiyama and Kubota , 2011
- Bathocyroe paragaster ( Ralph and Kaberry , 1950)
- Genus Bathocyroe Madin and Harbison , 1978
- Family Bolinopsidae Bigelow , 1912
- Genus Bolinopsis L.Agassiz , 1860
- Bolinopsis ashleyi Gershwin, Zeidler and Davie , 2010
- Bolinopsis chuni ( von Lendenfeld , 1884)
- Bolinopsis elegans ( Mertens , 1833)
- Bolinopsis indosinensis Dawydoff , 1946
- Bolinopsis infundibulum ( OFMüller , 1776)
- Bolinopsis mikado ( Moser , 1907)
- Bolinopsis ovalis ( Bigelow , 1904)
- Bolinopsis rubripunctata Tokioka 1964
- Bolinopsis vitrea ( L.Agassiz , 1860)
- Genus Lesueuria Milne Edwards , 1841
- Lesueuria hyboptera A. Agassiz , 1865
- Lesueuria pinnata Ralph and Kaberry , 1950
- Lesueuria tiedemanni ( Eschscholtz , 1829)
- Lesueuria vitrea Milne Edwards , 1841
- Genus Mnemiopsis L. Agassiz , 1860
- Mnemiopsis gardeni L. Agassiz , 1860
- Mnemiopsis Leidyi A. Agassiz , 1865
- Genus Bolinopsis L.Agassiz , 1860
- Family Leucotheidae Krumbach , 1925
- Genus Leucothea Mertens , 1833
- Leucothea filmersankeyi Gershwin, Zeidler and Davie , 2010
- Leucothea japonica Komai , 1918
- Leucothea multicornis ( Quoy and Gaimard , 1824)
- Leucothea ochracea Mayer , 1912
- Leucothea pulchra Matsumoto , 1988
- Genus Leucothea Mertens , 1833
- Family Ocyropsidae Harbison & Madin , 1982
- Genus Alcinoe Rank , 1828
- Alcinoe rosea Mertens , 1833
- Alcinoe vermicularis Rank , 1828
- Genus Ocyropsis Mayer , 1912
- Ocyropsis crystallina ( Rank , 1827)
- Ocyropsis fusca ( Rank , 1827)
- Ocyropsis maculata ( Rank , 1827)
- Ocyropsis pteroessa Bigelow 1904
- Ocyropsis vance Gershwin, Zeidler and Davie , 2010
- Genus Alcinoe Rank , 1828
- Family Eurhamphaeidae L.Agassiz , 1860
- Genus Eurhamphaea Gegenbaur , 1856
- Eurhamphaea chamissonis ( Eschscholtz , 1829)
- Eurhamphaea heteroptera ( Chamisso and Eysenhardt , 1821)
- Eurhamphaea kuhlii ( Eschscholtz , 1829)
- Eurhamphaea schweiggeri ( Eschscholtz , 1829)
- Genus Deiopea Chun , 1879
- Deiopea kaloktenota Chun , 1879
- Genus Kiyohimea Komai and Tokioka , 1940
- Kiyohimea aurita Komai and Tokioka , 1940
- Kiyohimea usagi Matsumoto and Robison , 1992
- Genus Eurhamphaea Gegenbaur , 1856
- Family Lampoctenidae Harbison, Matsumoto and Robison , 2001
- Genus Lampocteis Harbison, Matsumoto and Robison , 2001
- Lampocteis cruentiventer Harbison, Matsumoto and Robison , 2001
- Genus Lampocteis Harbison, Matsumoto and Robison , 2001
- Family Lobatolampeidae Horita , 2000
- Genus Lobatolampea Horita , 2000
- Lobatolampea tetragona Horita , 2000
- Genus Lobatolampea Horita , 2000
Species of the Lobata incertae sedis
- Axiotima gaedii Eschscholtz , 1829
- Calya trevirani Eschscholtz , 1829
literature
- GR Harbison , RL Miller: Not all ctenophores are hermaphrodites, Studies on the systematics, distribution, sexuality and development of two species of Ocyropsis. in: Journal of Marine Biology. 90.1986, p. 413.
- GI Matsumoto, GR Harbison: In situ observations of foraging, feeding, and escape behavior in three orders of oceanic ctenophores, Lobata, Cestida, and Beroida. in: Journal of Marine Biology. 117.1993, p. 279.
- TA Shiganova: Invasion of the Black Sea by the ctenophore Mnemiopsis Leidyi and recent changes in pelagic community structure. in: Fisheries Oceanography. Blackwell Science, Oxford 1997-1998, pp. 305. ISSN 1365-2419
Individual evidence
- ↑ Phylum Ctenophora: list of all valid species names, by Claudia E. Mills, accessed on April 25, 2017
