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Polychaete polychaetes (polychaetes): body shape and reproduction

Polychaete worms, they are also polychaetes, belong to the class of annelids and live mainly at the bottom of the seas. Only a few species are adapted to life in freshwater. Their role in the ecosystem is significant.

Polychaetes filter water, clean the soil from decomposing organic residues. In turn, the worms themselves become food for many fish, crustaceans, and echinoderms.

Bristle worms live at the bottom of the seas, and are rarely found in freshwater bodies of water.

According to reports from various sources, scientists are currently aware of 8–10 thousand species of polychaete worms. Some of them exist in a parasitic form, but most exist in the bottom zone or spend time buried in silt.

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Externally, this representative ringed can be described as follows:

  1. The length of polychaetes can be from 2 mm to 3 m.
  2. The body shape of polychaete worms consists of many segments, on the sides of which skin-muscular processes exist that help the polychaetes to move. These organs of motion are called parapodia. The worm swims near the bottom, curving with its body and scooping up muscular outgrowths.
  3. In addition, the head segment (prostomium) and caudal blade (pygidium) are isolated.
  4. Tentacles, palpi and antennae may be present on the head, all of which serve to polychaetes as organs of touch.

Among polychaete worms, there are sitting subspecies with a reduced number of parapodia, which are stored only in front of the body. These polychaetes live inside the protective tube built by them and never leave it.

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Internal organs and systems representative of ringed arranged as follows:

  1. Respiratory system. Polychaetes carry out gas exchange with the help of the entire surface of the body or make it the areas of parapodia in which there are blood vessels. The sedentary forms breathe with the help of tentacles on the head.
  2. Skin Muscular Bag. A thin cuticle covers the skin epithelium and the muscular layer, consisting of longitudinal and transverse muscles. Under the muscles is a layer of internal epithelium, forming partitions that separate the body of the worm into segments.
  3. Digestive organs. The digestive tract consists of: the mouth, muscular pharynx (often with chitinous teeth), the esophagus, the stomach and the intestines, which consists of three sections. The anal opening is located on the anal lobe. The sedentary forms of the polychaete worm feed on plankton and a suspension of organic particles. Free-living polychaetes are predators.

Sea worms carry out gas exchange with the whole body.

  • Circulatory system. The heart is missing. Blood moves through a closed system of blood vessels. It is driven by contractions of the main spinal vessel, in which blood moves back to front. In the second main vessel, the abdominal, the movement of the blood is the other way round – from front to back.
  • Nervous system includes the paired ganglia (representing the brain), located in the peripharyal ring, and the paired abdominal nerve chain with branches of nerves extending from it. Free-living polychaetes have organs of touch in the form of palps or tentacles and organs of equilibrium. Some species have eyes.
  • Excretory system. The organs of excretion are represented in the form of paired tubes present in each segment of the body. Through them, the waste products of the worm are displayed outside.
  • The larvae of worms are planktonic in the water column and are transported over long distances, so they are resettled. Initially, the trochophore consists of two hemispheres, gradually its body is drawn out and takes on a worm-like shape due to the growth of the larval (larval) segments.

    The growth zone is more often formed at the posterior end of the larva.

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    Most polychaete worms reproduces sexually. Egg cells are secreted by females and spermatozoa by males. The genitals of animals are developed in the peritoneal epithelium.

    Fertilization in most species occurs in the environment.

    As soon as the body segment is filled with matured germ cells, the epithelium is broken and they fall out. Other species for this there are special funnels – whole products.

    The fertilized larva is called the trochophora. Having settled on the bottom, after a while it turns into an adult.

    Sea worms reproduce sexually

    Only some forms have a complicated sexual apparatus that allows them to conduct copulation (for example, Saccocirrus). Many species of polychaete worms are characterized by reproduction by budding.

    At the same time, part of the body segments are separated and split into separate segments.

    In the future, each of them forms the head and anal parts, becoming an independent individual. This process is called archetymia.

    With paratomy, everything happens the opposite – a chain consisting of several individuals is separated. In the future, they are separated, becoming individually existing worms.

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    Marine polychaete worms inhabit saltwater bodies in large numbers and serve as food for many commercial breeds of fish. Polychaetes are the main diet of sturgeon sturgeon and sturgeon.

    Only when there is a shortage of polychaete worms does the fish transfer to other types of food and begin to eat shellfish, shrimps and other crustaceans. The Caspian, in which sturgeon fish are harvested, has for a long time only 5 species of polychaetes.

    A group of Soviet scientists carried out acclimatization in the Caspian Sea of ​​the polyrech nereis, which was brought from the Sea of ​​Azov. It is this worm that is distinguished by unpretentiousness and minimal requirements for the level of salinity of water.

    In the 40s of the last century, 65,000 polyrech nereis were released into the waters of the Caspian Sea, and by the end of the first decade the worms had occupied an area of ​​30,000 km2. This has significantly increased the biological value of the Caspian Sea.

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