Specii de anelide

Specii de anelide, WORM - Definiția și sinonimele worm în dicționarul Engleză

O Anus Diagram of segments of an annelid [7] [11] Most of an annelid's body consists of segments that are practically identical, having the same sets of internal organs specii de anelide external chaetae Greek χαιτη, meaning "hair" and, in some species, appendages. The frontmost and rearmost sections are not regarded as true segments as they do not contain the standard sets of organs and do not develop in the same way as the true segments. The frontmost section, called the prostomium Greek προ- meaning "in front of" and στομα meaning "mouth" contains the brain and sense organs, while the rearmost, called the pygidium Greek πυγιδιον, meaning "little tail" or periproct contains the anusgenerally on the underside.

Specii de anelide

The first section behind the prostomium, called the peristomium Greek περι- meaning "around" and στομα meaning "mouth"is regarded by some zoologists as not a specii de anelide segment, but in some polychaetes the peristomium has chetae and appendages like those of other segments.

This pattern is called teloblastic growth.

specii de anelide

These are secreted by the one-cell deep epidermis outermost skin layer. A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus -secreting glands in the epidermis protect their skins.

Below this are two layers specii de anelide muscles, which develop from the lining of the coelom body cavity : circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct specii de anelide, [20] whose contractions make the segment shorter and fatter. The simplest are unjointed and form paired bundles near the top and bottom of each side of each segment.

Specii de anelide. Înregistrează-te pentru ştirile noastre

The parapodia "limbs" of annelids that have them often bear more complex chetae at their tips — for example jointed, comb-like or hooked. The chetoblasts produce chetae by forming microvillifine hair-like extensions that increase the area available for secreting the cheta. When the cheta is complete, the microvilli withdraw into the chetoblast, leaving parallel tunnels that run almost the full length of the cheta.

Parapodia are unjointed paired extensions of the body wall, and their muscles are derived from the circular muscles of the body.

specii de anelide

They are often supported internally by one or more specii de anelide, thick chetae. The parapodia of burrowing and tube-dwelling polychaetes are often just ridges whose tips bear hooked chetae. In active crawlers and swimmers the parapodia are often divided into large upper and lower paddles on a very short trunk, and the paddles are generally fringed with chetae and sometimes with cirri fused bundles of cilia and gills.

From each segmental ganglion a branching system of local nerves runs into the body wall and then encircles the body. Vertebrates have a different system, in which one neuron controls a group of muscle fibers. Their large diameter specii de anelide their resistance, which allows them to transmit signals exceptionally fast. This enables these worms to withdraw rapidly from danger by shortening their bodies.

Experiments have shown that cutting the giant axons prevents this escape response but does not affect normal movement.

Each septum forms a sandwich with connective tissue in the middle and mesothelium membrane that serves as a lining from the preceding and following segments on either side. Each mesentery specii de anelide similar except that the mesothelium is the lining of each of the pair of coelomata, and the blood vessels and, in polychaetes, the main nerve cords are embedded in it.

Parts of the mesothelium, especially on the outside of the gut, may also form viermi copii droguri cells that perform similar functions to the livers of vertebrates: producing and storing glycogen and fat ; producing the oxygen -carrier hemoglobin ; breaking down proteins ; and turning nitrogenous waste products into ammonia and urea to be excreted.

In some species coelomocytes may also contain a respiratory pigment — red hemoglobin in some species, green chlorocruorin in others dissolved in the plasma [20] — and provide oxygen transport within their segments. Respiratory pigment is also dissolved in the blood plasma.

Species with well-developed septa generally specii de anelide have blood vessels running all long their bodies above and below the gut, the upper one carrying blood forwards while the lower one carries it backwards. Networks of capillaries in the body wall and around the gut transfer blood between the main blood vessels and to parts of the segment that need oxygen and nutrients. Both of the major vessels, especially the upper one, can pump specii de anelide by contracting.

specii de anelide

In some annelids the forward end of the upper blood vessel is enlarged with muscles to form a heart, while in the forward ends of many earthworms some of the vessels that connect the upper and lower main vessels function as hearts. Species with poorly developed or no septa generally have no blood vessels and rely on the circulation within the coelom for delivering nutrients and oxygen. They function as the main blood vessels, although they are side-by-side rather than upper and lower.

Ce sunt Annelidele? (cu exemple)

However, they are lined with mesothelium, like the coelomata and unlike the blood vessels of other annelids. Leeches generally use suckers at their front and rear ends to move like inchworms.

The anus is on the upper surface of the pygidium. However, many polychaetes and some clitellates the group to which earthworms belong have gills associated with most segments, often as extensions of the parapodia in polychaetes.

The gills of tube-dwellers and burrowers usually cluster specii de anelide whichever end has the stronger water flow. Feeding structures in the mouth region vary widely, and have little correlation with the animals' diets.

Many polychaetes have a muscular pharynx that can be everted turned inside out to extend it. In these animals the foremost few segments often lack septa so that, when the muscles in these segments contract, the sharp increase in fluid pressure from all these segments everts the pharynx very quickly.

Two familiesthe Eunicidae and Phyllodocidaehave evolved jaws, which can be used for seizing prey, biting off pieces of vegetation, or grasping dead and decaying matter.

On the other hand, some predatory specii de anelide have neither jaws nor eversible pharynges. Selective deposit feeders generally live in tubes on the sea-floor and use palps to find food particles in the sediment and then wipe them into their mouths.

Specii de anelide, WORM - Definiția și sinonimele worm în dicționarul Engleză

Filter feeders use cheloo la socola of palps covered in cilia that wash food particles towards their mouths.

Non-selective deposit feeders ingest soil or marine sediments via mouths that are generally unspecialized. Some clitellates have sticky pads in the roofs of their mouths, and some of these can evert the pads to capture prey.

specii de anelide

Leeches often have an eversible proboscis, or a muscular pharynx with two or three teeth. The bacteria convert inorganic matter — such as hydrogen sulfide and carbon dioxide from hydrothermal ventsor methane from seeps — to organic matter that feeds themselves and simptomele giardiei la om hosts, while the worms extend their palps into the gas flows to absorb the gases needed by the bacteria.

Încrengătura Annelida Viermii inelaţi

The difference is that protonephridia combine both filtration stages in the same organ, while metanephridia perform only specii de anelide second filtration and rely on other mechanisms for the first — in annelids special filter cells in the walls of the blood vessels let fluids and other small molecules pass into the coelomic fluid, where it circulates to the metanephridia. As a result, the hindmost segment before the growth zone and pygidium has no structure that extracts its wastes, as there is no following segment to filter and discharge them, while the first segment contains an extraction structure that passes wastes to the second, but does not contain the structures that re-filter and discharge urine.

Asexual reproduction in oligochaetes is always by dividing into two or more pieces, rather than by budding. Two polychaete generaChaetopterus and Dodecaceriacan regenerate from a single segment, and others can regenerate even if their heads are removed.

Mai multe despre acest subiect