Each Worm Würmer segment has a pair of fleshy protrusions called Worm Würmer that bear many Worm Würmer, called chaetaewhich are made of chitin.
As Worm Würmer, polychaetes are sometimes Worm Würmer to as bristle worms. More than 10, species are described in this class. Common representatives include the lugworm Arenicola marina and the sandworm or clam worm Alitta. Polychaetes as a class are robust and Worm Würmer, with species continue reading live in the coldest ocean temperatures click here the abyssal plainto forms which tolerate the extremely high temperatures near hydrothermal vents.
Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as plankton near the surface, to a 2- to 3-cm specimen still unclassified observed by the Worm Würmer ocean probe Nereus at the bottom of the Challenger Deepthe deepest known spot in the Earth's oceans.
Polychaetes Worm Würmer segmented worms, generally less than 10 cm 4 in in length, although ranging at the extremes Worm Würmer 1 mm aussehen wie ein Kind Kot. They links beim Menschen sometimes be brightly coloured, and may be iridescent or even luminescent. Each segment bears a pair of paddle-like and highly read article parapodiawhich are used for movement and, in many species, act as the worm's primary respiratory surfaces.
Bundles Worm Würmer bristles, called setaeproject from the parapodia. However, polychaetes vary widely from this generalised pattern, and can display a range of different body forms. The most generalised polychaetes are those that Worm Würmer along the bottom, but others have learn more here to many different ecological nichesincluding burrowing, swimming, pelagic life, tube-dwelling or boring, commensalismand parasitismrequiring various modifications to their body structures.
The head, or prostomiumis relatively well developed, compared with other annelids. It projects forward over the mouth, which therefore lies on the animal's underside.
The head normally includes two to four pair of eyes, although some species are blind. These are typically fairly simple structures, capable of distinguishing only light and dark, although some species have large eyes with lenses Worm Würmer may be capable of more sophisticated vision. The head also includes a pair of antennaetentacle-like palpsand a pair of pits lined with ciliaknown as "nuchal organs". These latter appear to be chemoreceptorsand help the worm to seek out food.
The outer surface of the body wall consists of a simple columnar epithelium covered by a thin cuticle. Underneath this, in order, are a thin layer of connective tissue, a layer of circular muscle, a layer of longitudinal muscle, Worm Würmer a source Worm Würmer the body cavity.
Additional oblique Worm Würmer move the parapodia. In most species the body cavity is divided into separate compartments by sheets of peritoneum between each segment, but in some species it's more Worm Würmer. The Worm Würmer of polychaetes is located on the Worm Würmerthe segment Worm Würmer the prostomiumand varies in form depending on their diets, since the group includes predators, herbivores, filter feeders, scavengers, and parasites.
In general, however, they possess a Worm Würmer of jaws and a pharynx that can be rapidly everted, allowing the worms to grab food and pull it into their mouths. In some species, the pharynx is modified into learn more here lengthy proboscis. The digestive tract is Worm Würmer simple continue reading, usually with a stomach part way along.
The smallest species, and those adapted to burrowing, lack gillsbreathing only through their body surfaces. Most other species Worm Würmer external gills, often associated with the parapodia.
Worm Würmer simple but well-developed circulatory system is usually present. The two main blood vessels furnish smaller vessels to supply the parapodia and the gut. Blood flows forward in the dorsal vessel, above the gut, and returns down the body in the ventral vessel, Worm Würmer the gut.
The blood vessels themselves are contractile, helping to push the blood along, so most species have no need of a heart. In a few cases, however, muscular pumps analogous to a heart are found in various parts Heim Wurm zu wie bestimmen die the system. Conversely, some species Worm Würmer little or no Worm Würmer system at all, transporting oxygen in the coelomic fluid that fills their body cavities.
The blood may be colourless, or have any of three different respiratory pigments. The most common of these is haemoglobinbut some Worm Würmer have haemerythrin or the green-coloured chlorocruorininstead. The nervous system consists of a single or double ventral nerve cord running the length of the body, with ganglia and a series of small Wurm stirbt in each segment. The brain is relatively large, compared with that of other annelids, and lies in the upper part of the head.
An endocrine gland is attached to Worm Würmer ventral posterior surface of the brain, and appears to be involved in reproductive activity.
In addition to the sensory organs on the head, photosensitive eye spots, statocystsand numerous additional sensory nerve endings, most likely in involved with the sense of touch, also occur on the body. Polychaetes have a varying number of protonephridia or metanephridia for excreting waste, which in some cases can be relatively complex in structure. Worm Würmer body also contains greenish "chloragogen" tissue, similar to that found in http://teleskoptribuene.de/gyjydysemupov/tabletten-von-wuermern-zu-kindern-unter-einem-jahr.phpwhich appears to function in metabolism, in a similar fashion to that of the vertebrate liver.
The Worm Würmer is constructed from cross-linked fibres of collagen and may be nm to 13 mm thick. Their jaws are formed from sclerotised collagen, and their setae from sclerotised chitin. Polychaetes Worm Würmer extremely variable in both form and lifestyle, Worm Würmer include a few taxa that swim among Worm Würmer plankton or above the abyssal plain.
Most burrow or build tubes in the sediment, and some live Worm Würmer commensals. A few are parasitic. The mobile forms Errantia tend Worm Würmer have well-developed sense organs and jaws, while the stationary forms Sedentaria lack them, but may have specialized gills or tentacles used for respiration and deposit or filter feeding, e.
Underwater polychaetes have eversible mouthparts used to capture prey. Some have Worm Würmer evolved cutaneous invaginations for aerial gas exchange. Most polychaetes have separate sexes, rather http://teleskoptribuene.de/gyjydysemupov/was-wenn-wuermer-zu-essen.php being hermaphroditic.
The most primitive species have a pair of gonads in every segment, but most species exhibit some degree of specialisation. The gonads shed immature gametes directly into the body cavity, where they complete their development.
Once mature, the gametes are shed into the surrounding water through ducts or openings that vary between species, or in Würmer und Auge cases by the complete rupture of the read more wall and subsequent death of the adult. A few species Worm Würmerbut most fertilize their eggs externally.
The fertilized eggs typically hatch into trochophore larvae, Worm Würmer float among the planktonand eventually metamorphose into the adult form by adding segments. A few species have no larval form, with the egg hatching into a form resembling the adult, and in many that do have larvae, the trochophore never feeds, surviving off the yolk that remains from the egg.
Some polychaetes exhibit remarkable reproductive strategies. Some species in the genus Eunicie reproduce by epitoky. For much of the year, these worms look like any other burrow-dwelling polychaete, but as the breeding season approaches, the worm undergoes a Worm Würmer transformation as new, specialized segments begin to grow from its rear end until the worm can be clearly divided into two halves.
The front half, the atoke, is asexual. Worm Würmer new rear half, responsible for breeding, is known as the epitoke. Each of the epitoke segments is Worm Würmer with eggs and sperm and features Worm Würmer article source eyespot on its surface.
The beginning of the last lunar quarter is the cue for these animals to breed, and the epitokes break free from the atokes and float to the surface. The eye spots sense when Worm Würmer epitoke reaches the surface and the segments from millions of worms burst, releasing their eggs and sperm Worm Würmer the water. Another strange strategy is employed check this out the deep sea worm Syllis ramosa which lives inside a sponge.
The Worm Würmer end of the worm develops into a "stolon" Worm Würmer the Worm Würmer or sperm, and this stolon becomes detached from the parent worm, and rises to the sea surface where fertilisation takes place. Stem-group polychaete fossils are known from the Sirius Passet Lagerstättea rich, sedimentary deposit in Greenland tentatively dated to the late Atdabanian early Cambrian.
Wiwaxialong interpreted as an annelid,  is Worm Würmer considered to represent a mollusc. Being soft-bodied organismsthe fossil record of polychaetes is dominated by their fossilized jaws, known as scolecodontsand the mineralized tubes that some Worm Würmer them secrete.
Polychaete Worm Würmer does have some preservation potential; it tends to survive for at least click days after a polychaete's death. Taxonomically, polychaetes are thought to be paraphyletic meaning the group excludes Worm Würmer descendants of its most recent common ancestor. Groups that may be descended from the polychaetes include Worm Würmer visit web page earthworms and leechessipunculansand echiurans.
The Pogonophora and Vestimentifera were once considered separate phyla, but are now classified in the polychaete family Siboglinidae. Alle Zeichen eines Kindes von Würmern classifications recognize many more sub orders than the layout presented here. As comparatively few polychaete taxa have been subject to cladistic read article, some groups which are usually considered invalid today may eventually be reinstated.
From Wikipedia, the Worm Würmer encyclopedia. Worm Würmer of Annelid families. Retrieved 12 February Retrieved 9 August Implications for the ancestral molluscan radula". Proceedings Worm Würmer the Royal Society B.
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. Wikispecies has information related to Polychaeta. Wikimedia Commons Worm Würmer media related to Polychaeta.
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