Nuda
Encyclopedia
Nuda is a class of comb jellies. As their name implies, they are distinguished from other comb jellies by the complete absence of tentacles. Nudans are found in all the world's oceans and seas, where they swim freely in the plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

.

Anatomy

Nuda often reach a length of up to 30 centimetres (11.8 in), with Neis cordigera often referred to as the largest type. The sack-like body of the Beröe species is easily compressed perpendicular to the plane of the gap, while Neis is flattening by training two "wing" even more pronounced.

Like other comb jellies, the body wall of nudans consists of an outer epidermis
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...

 and an inner gastrodermis, separated by a jelly-like mesoglea
Mesoglea
Mesoglea is the translucent, inert, jelly-like substance that makes up most of the bodies of jellyfish, comb jellies and certain primitive sea creatures in the phyla Cnidaria and Ctenophora. It acts as the creatures' structural support in water, as they lack bones or cartilage, endo- or...

. The mesoglea has pigments that give many nudan species a slightly pink color; for example, Neis cordigera is strong orange-red.

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 seal firmly by a zip-like mechanism, so that the ctenophore attains a streamlined front. 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.

Nudans have only smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

 fibres.

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
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 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 the typical eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 construction of nine external and two internal microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...

s.

The scourge cells, in which the cilia from individual basal bodies
Basal body
A basal body is an organelle formed from a centriole, and a short cylindrical array of microtubules. It is found at the base of a eukaryotic undulipodium and serves as a nucleation site for the growth of the axoneme microtubules...

 arise, to the Schlundauskleidung by an average of thirty degrees to mundabgewandten side and, stacked on top like roof tiles. Thus, the macrocilia always point in the direction of the interior of the throat. 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 to rip even larger prey like other ctenophores; proteolytic
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...

 enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 penetrate into the resulting wounds, 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 ctenophore 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, statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...

, including the clock for the ribs arranged on the ridge platelets determine. The shock pulse, unlike in the Lobata
Lobata
Lobata is an order of Ctenophora in the class Tentaculata with smaller tentacles than other ctenophores, and distinctive flattened lobes extending outwards from their bodies.They are about long.-Anatomy:...

, 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 statocyst is an inlet lined with sensory cells, which 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 statocyst 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 sensory perception.

Unlike other groups of ctenophores put them to continue their movement almost exclusively comb ribs.

Diet

Nudans feed on free swimming animals with soft bodies, primarily from other ctenophores, certainly larger than they themselves can be. They actively hunt for prey, which they usually devour whole. Some species use their macrocilia as teeth to take smaller chunks from the prey.

As invasive species

In the late 1980s the ctenophore species Mnemiopsis leidyi
Mnemiopsis leidyi
The warty comb jelly or sea walnut is a species of tentaculate ctenophore , originally native to the western Atlantic coastal waters. Three species have been named in the genus Mnemiopsis, but they are now believed to be different ecological forms of a single species M...

was introduced into the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

, probably through ballast water, which led to the collapse of the local anchovy
Anchovy
Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...

 population. In 1997 another ctenophore species arrived--Beroe
Beroe
Beroe is a Procurement intelligence company which works for fortune 500 companies.Positioned at the forefront of procurement intelligence operations and customized market research, Beroe is unique in its 100% exclusive focus on procurement....

 ovata
, a predator of Mnemiopsis leidyi. The Beroe population underwent an initial explosion, until the numbers of both ctenophores stabilized. Nevertheless, both Mnemiopsis leidyi and Beroe ovata remain today in the Black Sea. The same phenomenon is occurring at the beginning of the 21st century in the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

.

Reproduction

All species reproduce sexually, and have both female and male gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

. Although no detailed figures are available, it is assumed that self-fertilization is the exception among nudans.

The fertilized eggs hatch into miniature versions of the adult animal, rather than distinct larval forms. They already lack the tentacles and Tentakelscheiden, otherwise they are similar to the Cydippea stadum.

History of the species

There are no known fossil nudans, so the phylogenetic evolution of the group from the comparison with other modern representatives of Rippenquallen tapped to be. In the traditional system, the Nuda form a class distinct from the Tentaculata
Tentaculata
Tentaculata is a class of comb jellies. The common feature of this class is a pair of long, feathery, contractile tentacles, which can be retracted into specialised ciliated sheaths. In some species, the primary tentacles are reduced and they have smaller, secondary tentacles...

, which all have at least rudimentary tentacles. This division, after provisional results of morphological and molecular studies, however, probably does not reflect the actual relationships within the ctenophores.

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
Cydippida
Cydippida is an order of comb jellies. They are distinguished from other comb jellies by their spherical or oval bodies, and the fact their tentacles are branched, and can be retracted into pouches on either side of the pharynx.-Anatomy:...

, Haeckelidae, in the closer relationship of Nuda species to belong neither Cydippida still Tentaculata would therefore cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

 taxa included not all offspring of their joint Vorfahrens and would therefore is not recognised as a valid taxon in modern schemes.

The monophyly of Nuda itself, is however widely accepted, due to the complete lack of tentacles, and the presence of macrocilia as a common secondary feature, or synapomorphy
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

.

Systematics

There are approximately 25 species, grouped into two genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 in the single family Beroidae. The family and order were named in 1825 or 1829 by the German naturalist Johann Friedrich Eschscholtz
Johann Friedrich von Eschscholtz
Johann Friedrich Eschscholtz was a Livonian physician, botanist, zoologist and entomologist.Eschscholtz was born in Dorpat , Governorate of Livonia in the Russian Empire...

.
  • The genus Beröe includes nearly all types of class and is distributed worldwide. One of the best known is reflected in the North
    North
    North is a noun, adjective, or adverb indicating direction or geography.North is one of the four cardinal directions or compass points. It is the opposite of south and is perpendicular to east and west.By convention, the top side of a map is north....

     spread Melonenqualle (Beröe gracilis). In Beröe species is mundabgewandte (aboral) side down.

  • The genus Neis is monotypical, containing only one species, Neis cordigera(Lesson 1824), and is found 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 ctenophore typical eight ribs number of bands is obtained, even if the tapes because of the particular body shape into two different groups - long training.
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