Definitions

class nuda

Nuda

Nuda is a class of Ctenophora known as comb jellies, and refers to the characteristic feature of representatives of this taxon, the lack of tentacles.

Anatomy

The Mesoglea - the jelly-like intermediate layer between the inner and outer skin (epidermis and Gastrodermis) - has pigments that give many Nuda species a slightly pink color. Neis cordigera is strong orange-red. Nuda often reach a length of up to about thirty centimeters, with Neis cordigera often referred to as the largest type. The sack-like body of the Beroe species perpendicular to the plane of the gap is easily compressed, Neis is flattening by training two "wing" even more pronounced (more on this in the systematics).

The eponymous and defining characteristic of Nuda is the complete absence of tentacles, unlike individuals of the related Tentaculata class.

Mouth opening and muscles

As prey as a whole with his mouth devoured, has this and the subsequent jump gap including one in comparison to other ctenophores a large diameter. In order for swimming, and especially in the pursuit of prey in the water to reduce resistance, it can through a reißverschlussähnlichen mechanism firmly sealed, so that the front of ctenophore streamlined form accepts. This will close the opposite sides of the gap, the "lips", not only brought in close contact, but by temporarily trained cell-cell connections closely interlinked. The whole ctenophore own nerve network is within the "lip" of a Nuda of about 40 nerve cell Fort records (Neurit), this bundle of compacted.

The palate is caused by the interplay of three different types of muscle open and closed: In the Mesoglea lost both ring around the longitudinal axis of the animal and arranged radial, radially outwards from the inside running muscle fibers; they interact with longitudinal, so längsseitig oriented fibers, which the epidermis. Nuda species has only smooth muscles.

Macrocilia

Directly inside the mouth opening can be found in the lining of the gap characteristic finger-like excesses, Macrocilia. In this first 1844 of JGF Will described and 1965 by George Adrian Horridge with her today named structures are conical shaped by a common plasma membrane surrounded bundles of two to three scourges (cilia), which, as in the comb plates of ribs to a functional unit connected. The individual, between 35 and 60 micrometres in diameter long and 5 to 10 micrometres thick cilia together in a hexagonal cross-sectional structure, and are perpendicular to the direction of common connected by crossbars, a separate membrane, which they divide their neighbor scourges would have it they are not. Each Cilium shows for the organisms with real nucleus typical construction of nine external and two internal microtubules.

The scourge cells, in which the cilia from individual basal body arise, to the Schlundauskleidung by an average of thirty degrees to mundabgewandten side and, like roof tiles stacked on top. Thus, the macrocilia always points in the direction of the throat interior. This is where is the effective strike, which is prey parts in synchronized waves like a conveyor belt transported in the stomach and the throat muscles promoted this process.

Macrocilia run in a three toothed top of this is stiff enough to the soft outer wall even larger prey like other ctenophores to rip; proteolytic enzyme, in the resulting wounds penetrate, make the victim then quickly escape. Macrocilia also function as teeth, and can be used in the same way as the tentacles of Tentaculata.

Affairs channel system

From the main drag from stomach like all cteophore channels in all regions of the body. Each rib will comb through its own meridional canal furnished directly below this location. He owns at the Nuda species many fine ramified excesses, some of which deal with the gap unite, but others end up blind. To that end mouth running the meridional canal in a circle around the mouth lying ring channel.

Statocyste and polepieces

As with all ctenophores is at the mundabgewandten side Gleichwichtsorgan, Statocyste, including the clock for the ribs arranged on the ridge platelets determine. The shock pulse is unlike in the Lobata is not through the ridge between platelets oblique scourge forwarded tapes, but the fact that the individual comb platelets in turn fall, like dominoes, the subsequent platelet influence.

Immediately below the Statocyste is a sensory cells lined inlet, which it contains epithelial tissue has to mouth out in two opposite narrow bands scourge continues, in the throat level of ctenophore run and as a polepieces. You call a strike by its water flow on the Statocyste shows and are used by the Nuda-Arten at its border with finger excesses, the papillae occupied whose function is still unclear, but probably also the sensory perception.

Distribution and habitat

The group comes in all the world's oceans and seas, where the animals free swimming in the plankton live. Unlike other groups of cteophores put them to continue their movement almost exclusively comb ribs.

Diet

Nuda feed on free swimming animals with soft bodies, primarily from other cteophores, certainly larger than they themselves can be. The booty will be actively sought and usually devoured as a whole; in size, the animals can their macrocilia as teeth used to make tissue pieces from the victim herauszureißen.

Importance as Neozoon

Once in the late 1980 years cteophore species Mnemiopsis leidyi probably through ballast water into the Black Sea introduced, and there was a population explosion through, in the course of which anchovies - fishing completely collapsed, stabilized the ecosystem again, as 1997 a further cteophore species appeared to be the Nuda counted Beroe ovata, which are almost exclusively from Mnemiopsis leidyi diet. The Beroe population underwent an initial explosion of the number of individuals until both stocks rapidly brought together. Nevertheless, both Mnemiopsis leidyi and Beroe ovata today than Neozoen established in the Black Sea. The same phenomenon takes place at the beginning of the 21 century Caspian Sea.

Reproduction

All species reproduces sexually, and have continued on both female and male gonads on, so hybrid. Although no detailed figures are available, it is assumed that self-fertilization in Nuda rather the exception. The fertilized eggs are young animals that are already like a miniature version of the adult animal look like and therefore not be described as a larva. You already missing tentacles and Tentakelscheiden, otherwise they are similar to the Cydippea stadum the tentaclecontaining ctenophores.

History of the species

Fossil Nuda species are not known, so that the phylogenetic evolution of the group from the comparison with other modern representatives of Rippenquallen tapped to be. In the traditional system, the Nuda the class of Tentaculata against which all types summarizing, in contrast to the Nuda species at least rudimentary tentacles. This division, after provisional results of morphological and molecular studies, however, probably not the actual relationships within the ctenophores again. Although the scheme is still in the river and does not have an independent assessment of the available evidence, seems to be a family from the order Cydippida, Haeckelidae, in the closer relationship of Nuda species to belong neither Cydippida still Tentaculata would therefore cladistic taxa included not all offspring of their joint Vorfahrens and would therefore of the modern systematics is not recognized as a valid taxon.

The monophyly of Nuda itself, is however widely accepted on the complete lack of tentacles, and the presence of macrocilia as a common secondary feature (synapomorphy).

Systematics

There are approximately 25 species, based on two genera, Beroe and Neis divide, which in the same Family Beroidae and Rules Beroida be. Family and order were 1825 or 1829 by the German naturalists Johann Friedrich Eschscholtz.

  • The genus Beroe includes nearly all types of class and is distributed worldwide. One of the best known is reflected in the North spread Melonenqualle (Beroe gracilis). In Beroe species is mundabgewandte (aborale) side down.
  • The genus Neis is monotypical, contains only one species, Neis cordigera(Lesson 1824), and comes only in the waters around Australia. In this type are located on the aboralen page two bogenartige progress rates, so that the middle intermediate aborale Sinnespol unlike the Beroiden not at the extreme end of the body is located (Note Artname cordigera: heart). The bogenartigen Fort sentences extend along the flanks of the animal and are Längsverlauf divided so that the impression of two sides "double wings". At the edges of these four "wings" is one rib band. The remaining four ribs on the lost tapes (relative to the "side wings") "upper" and "lower" body half. The cteophore typical eight ribs number of bands is obtained, even if the tapes because of the particular body shape into two different groups - long training.

References

  • G. I. Matsumoto, GR Harbison:In situ observations of foraging, feeding, and escape behavior in three orders of oceanic ctenophores: Lobata, Cestida, and Beroida.Marine Biology. '117 ', 1993, p. 279th
  • S. Tamm, SL Tamm:A giant nerve net with multieffector synapses underlying epithelial adhesive strips in the mouth of Beroe.In the Journal of Neurocytology. '24 ', 1995, p. 711st
  • S. Tamm, SL Tamm:Dynamic control of cell-cell-adhesion and membrane-associated actin during food-induced mouth opening in Beroe.In the Journal of Cell Science. '106 ', 1993, p. 355

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