The respiratory organs of polychaetes are. Polychaete worms: a brief description of the class. excretory and respiratory systems
Class Polychaete worms (Polychaeta)
Audio fragment "Class Polychaete worms" (00:57)
About 7 thousand species of polychaete worms are known. Most of them live in the seas. Few live in fresh waters, in litter rainforest. In the seas polychaete worms live at the bottom, where they crawl among stones, corals, thickets of marine vegetation, burrow into the silt. Among these worms there are sessile forms that build a protective tube and never leave it. There are also planktonic species among them. Polychaete worms are found mainly in the coastal strip, but sometimes at a depth of up to 8 thousand m. In some places, up to 90 thousand polychaete worms live on 1 m 2 of the seabed. They are eaten by crustaceans, fish, echinoderms, coelenterates, birds. Therefore, some polychaete worms were specially bred in the Caspian Sea as food for fish.
The length of polychaete worms is from 2 mm to 3 m. The body is elongated, slightly flattened in the dorsal-ventral direction or cylindrical. Just like others annelids, the body of polychaetes consists of segments, the number of which is different types ranges from 5 to 800. In addition to many trunk segments, there is head office
and anal lobe
.
On the head of these worms are a pair palps (palps) , pair tentacles (antennae) and antennae . These are the organs of touch and chemical sense.
On the sides of each segment of the body, muscular outgrowths are noticeable - the organs of movement, which are called parapodia
(from Greek. pair- "near" and podium- "leg"). Parapodia contain a kind of reinforcement - bundles of bristles that contribute to the rigidity of the organs of movement. The worm rakes its parapodia from front to back, clinging to the irregularities of the substrate, and thus crawls forward.
In sessile forms of worms, a partial reduction of the parapodia occurs: often they remain only in the anterior part of the body.
The body of oligochaete worms is covered with a single-layered epithelium. In sessile forms of worms, the secretions of the epithelium can harden, forming a dense protective sheath around the body. The skin-muscular sac consists of a thin cuticle, skin epithelium, annular and longitudinal muscles.
Under the skin epithelium there are two layers of muscles: transverse, or annular, and longitudinal. Under the layer of muscles there is a single-layer epithelium, which from the inside lines the secondary cavity of the body, or the whole, and also forms partitions between the segments.
Digestive system begins with the mouth, which is located on the ventral side of the head lobe. The intestine consists of three sections: the anterior, middle and hindgut.
In the muscular throat of many predatory worms there are chitinous teeth used to capture prey. The middle intestine is in the form of a straight tube. The anal opening is located on the anal lobe. Stray polychaete worms are mainly predators, while sessile ones feed on small organic particles and plankton suspended in water.
Respiratory system. In polychaete worms, gas exchange is carried out either by the entire surface of the body, or by sections of parapodia, into which blood vessels enter. In some sessile forms, the corolla of tentacles on the head lobe performs the respiratory function.
Circulatory system in annelids it is closed. This means that in any part of the body of the worm, blood flows only through the vessels. There are two main vessels - dorsal and abdominal .
One vessel passes over the intestine, the other - below it. They are connected to each other by numerous semicircular vessels. There is no heart, and the movement of blood is provided by contractions of the walls of the spinal vessel, in which blood flows from back to front, in the abdominal - from front to back.
excretory system presented paired tubules located in each segment of the body. Each tube begins with a wide funnel, the edges of which are covered with shimmering cilia. The funnel faces the body cavity, and the opposite end of the tube opens outward on the side of the body. With the help of a system of tubules, the decay products that accumulate in the coelomic fluid are brought out.
Nervous system consists of paired supraglottic, or cerebral, nodes, a paired abdominal nerve trunk and nerves extending from them.
sense organs most developed in vagrant polychaete worms. Many of them have eyes (in some species even capable of accommodation). The organs of touch and chemical sense are located on the antennae, palps, antennae and parapodia. Polychaete worms have balance organs (statocysts). Some species are capable of luminescence.
Reproduction. Most polychaete worms separate sexes . Sex glands are formed in almost every segment. Mature germ cells (in females - eggs, in males - spermatozoa) first enter as a whole, and then through the tubules excretory system taken out into the water. Fertilization in polychaete worms external ; the parents then die. After crushing, the planktonic larva develops from the eggs, which swims with the help of cilia. After a while, it settles to the bottom, and then turns into an adult worm. Some species are observed mating games and fighting for territory.
Some polychaete worms also have asexual reproduction . The worm is divided across, and then each half restores the missing part of the body. In this case, a temporary chain is sometimes formed, including up to 30 worms.
Polychaete worms (for example, nereis, 2 ) serve as food for many fish. Some worms ( palolo) are consumed by humans.
Setae arranged along kam of each segment are org us movement. Against the backdrop of many trunk segments stands out fishing department. On it are located sense organs (palpi, antennae, other yes eyes). Ends body anal blade.
General characteristics. Polychaete worms are the most ancient group type of annelids, which gave rise to other classes of this type. The reason for the name of the class was the fact that these worms on the sides of the body segments formed peculiar organs - parapodia, equipped with numerous bristles.
The body of polychaete worms consists of a number of outwardly similar segments. The anterior segments, merging, form a well-defined head section, on which the mouth and various appendages are located, as well as some sensory organs. Animals are dioecious. Develop with metamorphosis (Fig. 106). Several thousand species have been described. Have practical value as fish food.
Rice. 106. Pitchfork of multi-brush annelids:
/ - peskozhil
(Arenieola);
II yersis (Nereis); 111 -
phyllodosch1
(I"
ln/
lodoce);
IV.....-■ Amphitrigo (Amphitrite);
V-
sabellarin
(Suhellariu);
VI- herpula
(Serptilci),
VII marine mnpp>
(Aphrodite);
I- tentacles; 2 -
gills; 3
........ paranodpi
Structure and vital functions. The body length of polychaete worms ranges from a few millimeters to 1 m or more.
The organs of movement are narapodium - paired lateral outgrowths, usually consisting of an unpaired main part and two lobes: dorsal and abdominal (Fig. 107). Each lobe contains a bundle of elastic bristles, as well as a usually tactile barbel. With underdevelopment of the dorsal lobe, the parapodia become single-branched. Parapodia are used by worms when crawling along the bottom of a reservoir, and when an animal swims, they play the role of fins. In worms that burrow in the ground or live in tubular houses, the parapodia are completely or partially reduced.
The covers of polychaete worms, leading an active life at the bottom of the reservoir, are distinguished by a well-developed cuticle. On the contrary, in worms that swim in the water column, burrow into the ground or build tubular houses, the cuticle is very thin. The secretions of the integument serve as a building and cementing material in the construction of tubes in which some polychaete worms live.
The sense organs of most mogochaete worms are well developed. On the head (Fig. 108) there are usually 1-2 pairs of eyes, tactile antennae, tentacles and olfactory pits.
Respiratory organs - gills. In some, they are absent, and breathing takes place over the entire surface of the body.
Reproductive organs. Polychaete worms usually have separate sexes, there are no external differences between the sexes. At certain types parthenogenesis occurs. Most lay eggs, but there are also viviparous forms. Some reproduce by budding, which may result in the formation of temporary branched colonies.
Rice. 108. Head of polychaete annelids nereis:
The development of polychaete worms occurs with or without metamorphosis. In most forms, microscopically small floating larvae emerge from eggs - trochophores, which have a rounded, non-segmented body with bands of cilia. At first they have a primary body cavity, which in the process of animal development is replaced by a secondary one.
Polychaete worms inhabit the seas, living from shallow water to great depths. Some representatives are found in freshwater basins, for example, in Lake. Baikal. Most species live on the bottom, but some live in the water column. Some are very mobile and able to crawl along the bottom and swim, others burrow into the ground, others constantly live in a tubular house built of lime or organic substances secreted by the integument of the worm.
Each of environmental groups polychaete worms have their own organizational features, feeding methods, protective devices. Those living in houses usually have underdeveloped iaranodes, their head tentacles, merging, can form a lid that closes the entrance to the house. The tentacles of some sessile species take on a pinnately branched form; they act as gills and are involved in obtaining food. Their surface is covered with ciliated epithelium, the cilia of which drive water with food particles suspended in it to the mouth. For the resettlement of such attached worms, a free-swimming larva serves.
Some burrowing polychaetes have a toothed proboscis to help them burrow. Their parapodia are often atrophied, and short setae protrude directly from the body in tufts.
Many species of polychaetes serve as the main food for commercial marine fish. Therefore, their distribution and abundance are taken into account when assessing the biological productivity of water bodies and exploration of reserves. commercial fish. Of the annelids, which are food for fish, those living in shallow water are important Nereids (Nereis). At the suggestion of prof. L. A. Zenkevich in 1939-1941. they were relocated from Sea of Azov to the Caspian, where they were not previously found. Nereids have taken root well in the new conditions and have now become a valuable food for sturgeons in the Caspian Sea.
Peculiar polychaete worm peskozhil (ArenicolaMarina) inhabits sandbanks in large numbers. It lives in silted sand, passing it through the intestines and digesting the organic matter contained in it.
The Pacific worm palolo (Euniceviridis) during the breeding season, segments of the back of the body, filled with reproductive products, come off and float to the surface of the sea. By breaking the walls of the segments, the eggs contained in them or
spermatozoa are released into the water, where they are combined. From the zygotes, floating larvae develop, and from them - adult worms that sink to the bottom. Such reproduction contributes to the resettlement of sedentary worms. During the period of mass ascent, the local population extracts them in in large numbers and use it as food.
πολύς - a lot, Greek. χαίτη - hair) - a class of annelids. Currently, this class has more than 10 thousand species. Most famous representatives: sandstone Arenicola marina and nereid Nereis virens.Encyclopedic YouTube
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✪ Biology 7 Type Annelids Class Polychaetes
✪ Polychaete worms. Biology Grade 7.
✪ Zoology: Marine polychaete worms
Subtitles
Habitat
The vast majority of representatives are inhabitants sea waters. Adults, as a rule, are bottom forms, although some representatives have moved to living in the pelagic zone (for example, the family Tomopteridae). Very few polychaetes have moved to living in fresh water (for example, the genus Manayunkia in Lake Baikal), in forest litter and in soil at a depth of more than 3 m (genus Parergodrilus and genus Hrabiella).
body structure
Length from 2 mm to 3 m. The body consists of many (sometimes up to several hundred) rings-segments, each of which repeats the complex internal organs: paired coelomic sacs, associated genital ducts and excretory organs.
A distinctive feature is parapodia - lobe-like appendages extending from each segment of the body, bearing chitinous bristles (haetae). In some species, the function of the gills is performed by the corolla of tentacles on the head section. There are eyes, sometimes complex, and balance organs (statocysts).
Food
Among the sedentary polychaetes, sedimentators are the most common (for example, representatives of the families Sabellidae, Serpulidae, Spirorbidae). They feed on detritus, extracting it with the help of trapping tentacles, which also perform the function of gills, from the water column.
Free-living (errant) polychaetes are detritivores or predators. Detritophages can extract organic matter from the soil by eating it, for example, representatives of the families Arenicolidae, Ampictenidae. Some collect detritus from the ground surface with long palps (for example, Spionidae). Predation is widespread, for example, among Nereididae, Glyceridae, Syllidae.
reproduction
Most often, polychaete worms are dioecious animals. Polychaetes do not develop well-formed gonads. Sex cells develop from the coelomic epithelium, and after maturation, they proceed to float into the coelom cavity. Fertilization is external. The larva emerges from the eggs - trochophore.
After a short swim, the trochophore sinks to the bottom, where it metamorphoses into a three-layered animal. Her back end is pulled out and segments are immediately formed. The first segments are called larval; later gonads are not formed in them. At further development metatrochophores, the posterior end is extended and separates from itself segments, which are called postlarval.
Thus, a pair of coelomic sacs is formed in each segment. The parietal plate develops into the supraesophageal ganglion. From the ectoderm, the cuticle and hypodermis also develop (the layer of the integument of the body, usually lying deeper than the surface layer).
Protonephridia disappear, metanephridia associated with the coelom develop. Muscles, the circulatory system, coelomic fluid and some other organs are formed from the rudiments.
Some species are able to reproduce asexually. There are two types of asexual reproduction: archetomy and paratomy. In the case of archetomy, the body of the worm is first divided into fragments, and then completes the front and rear ends of the body. Paratomy, on the other hand, implies a reverse sequence of events: during this process, a chain of worms linked to each other by opposite ends of the body is formed.
Polychaete worms (polychaetes)- this is a class belonging to the type of annelids and includes different sources from 8 to 10 thousand species.
Representatives of polychaetes: nereid, sandworm.
The length of polychaete worms varies from 2 mm to 3 m. The body consists of a head lobe (prostomium), trunk segments, and a caudal lobe (pygidium). The number of segments is from 5 to hundreds. On the head are palps (palps), tentacles (antennae) and antennae. These formations play the role of organs of touch and chemical sense.
Almost every segment of the body polychaete worm has skin-muscular outgrowths (on the sides). These are parapodia - organs of locomotion. Their rigidity is provided by a bundle of bristles, among which there are support ones. In sessile forms, the parapodia are mostly reduced. Each parapodia consists of upper and lower branches, on which, in addition to setae, there is a tendril that performs tactile and olfactory functions.
With the help of muscles attached to the walls of the secondary cavity, parapodia perform rowing movements.
Polychaete worms swim by moving the parapodia and bending the body.
The body is covered with a single-layered epithelium, the secretions of which form cuticles. In sessile species, the epithelium secretes substances that harden to form a protective sheath.
The skin-muscular sac consists of the skin epithelium, cuticle and muscles. There are transverse (ring) and longitudinal muscles. Under the muscles there is another layer of a single-layer epithelium, which is the lining of the coelom. Also, the inner epithelium forms partitions between the segments.
The mouth is located at the head of the worm. There is a muscular pharynx that can protrude from the mouth, many predatory species with chitinous teeth. In the digestive system, the esophagus and stomach are separated. The intestine consists of the anterior, middle and hindgut.
The midgut looks like a straight tube. It digests and absorbs nutrients into the blood. Fecal masses are formed in the hindgut. The anal opening is located on the caudal lobe.
Breathing is carried out through the entire surface of the body or by folded protrusions of parapodia, in which there are many blood vessels (peculiar gills). In addition, outgrowths that perform a respiratory function can form on the head lobe.
The circulatory system is closed. This means that the blood moves only through the vessels. Two large vessels - dorsal (above the intestine, blood moves towards the head part) and abdominal (under the intestine, blood moves towards the tail part). The dorsal and abdominal vessels are interconnected in each segment by smaller annular vessels.
There is no heart, the movement of blood is provided by contractions of the walls of the spinal vessel.
The excretory system of polychaete worms is represented in each segment of the body by paired tubules (metanefridia), which open outward in the adjacent (behind) segment. In the body cavity, the tubule expands into a funnel. Along the edge of the funnel are ciliated cilia, which ensure that waste products from the coelom fluid enter it.
Paired supraesophageal ganglia are connected to form a peripharyngeal ring. There are a pair of ventral nerve trunks. In each segment, nerve knots are developed on them, thus abdominal nerve chains are formed. Nerves depart from the ganglia and abdominal nodules. The distance between the abdominal chains is different in different species of polyshedines. The more evolutionarily progressive the species, the closer the chains are, one might say, merge into one.
Many mobile polychaete worms have eyes (several pairs, including eyes, are on the caudal lobe). In addition to antennae and antennae, there are organs of touch and chemical sense on the parapodia. There are organs of balance.
Most are segregated. Usually the sex glands are present in each segment. The eggs and spermatozoa are first in the whole, from where they enter through the tubes of the excretory system or ruptures in the body wall. environment. Thus, fertilization in polychaete worms is external.
A trochophore larva develops from a fertilized egg, swimming with the help of cilia, having a primary body cavity and protonephridia as excretory organs (in this way it resembles the structure of ciliary worms). Settling on the bottom of the trochophore turns into an adult worm.
There are species of polychaetes that can reproduce asexually(dividing across).
Workshops
Laboratory work.
Topic: Structural features of polychaete worms
Target: study morphological and anatomical features structures of polychaete worms associated with the environment and lifestyle.
1. Systematics
Type of Annelida worms
Subtype Beltless Aclitellata
Class Polychaeta Polychaeta
Subclass Stray Errantia
View Nereis Nereis pelagica
Subclass Sedentaria
View Peskozhil Arenicola Marina
2. Theoretical information
Type annelids (Annelida)
Among all worms, annelids are the most highly organized group of worms. In the organization of annelids, much appears for the first time. For the first time, they have a real segmentation of the body, that is, the body is not only outside, but also inside with special partitions - dissipations are divided into segments. The head section of the body appears, which is represented by two lobes. In general, their body is divided into 3 sections: the head, the segmented torso and the posterior section of the body - the pygidium, or anal lobe. Most of them have homonomous segmentation, that is, all segments are the same, or almost the same, in contrast to the heteronomous segmentation characteristic of more organized animals.
Annelids are the first animals to develop a secondary body cavity, the coelom. As a whole, it performs an excretory function, substances are diffusely transported in it and sexual products mature.
Digestive system consists of three functionally different sections: anterior, middle and hindgut. Part of annelids has salivary glands associated with the foregut. The walls of the intestine in the rings, in contrast to roundworms formed not by one layer of cells, but by several.
Respiratory system in annelids, as in other types of worms, it is absent, and gas exchange occurs through the entire surface of the body, although some, such as polychaetes, have outgrowths of the body, which are considered as primitive gills. However, they have a circulatory system; it consists of blood vessels, they permeate their entire body and form plexuses in all tissues.
There is no heart, and its function is performed by the dorsal blood vessel, the walls of which periodically pulsate and drive blood to the front end of the body, while blood flows in the opposite direction through the abdominal blood vessel. These two main vessels are connected in each segment by annular blood vessels, which in some (polychaetal) may also pulsate. Blood carries throughout the body nutrients coming from the digestive organs and oxygen coming through the integument of the body.
excretory system metanephridial type. It is represented by independent segmental excretory tubules. In each segment as a whole, the excretory tube opens with a funnel, which, penetrating the wall of the dissipation, opens outward with an opening in the next segment. Metanephridia connect the whole with external environment, so they are also called coelomoducts. The decay products enter the coelomic fluid, where they accumulate and are excreted through the metanephridia. Usually, each segment has a pair of metanephridia.
Nervous system consists of paired head ganglia, which are called the "brain", located dorsally above the pharynx. Two nerve trunks depart from the "brain", connecting it with the first pair of nodes of the ventral nerve chain, bending around the pharynx on both sides.
sense organs represented separate structures, visual (eyes) and olfactory pits. Annelids reproduce asexually and sexually. Asexual reproduction occurs by fission.
Usually these are dioecious animals, reproduction occurs by division, but often they develop both male and female gonads, that is, hermaphroditism is observed. Their development is direct, (that is, a small worm comes out of the egg), in others - with metamorphosis, a floating larva is formed - a trochophore, which is not at all like an adult.
Thus, in the organization of annelids, a number of signs are observed that allow them to be attributed to the group of higher worms:
The presence of a coelom, real metamerism, a more complex structure of the nervous system and sensory organs, the presence circulatory system and primitive respiratory organs, excretory organs of the metanephridial type. In all these features, they differ from flat and round worms.
However, it should be noted that annelids also have some signs of lower worms. The larva of annelids - trochophore has a primary cavity, excretory organs - protonephridia, an orthogonal nervous system, and at the first stages of development of the larva, its intestines are closed. All of these signs are sometimes found in adult annelids.
The type of annelids is divided into two subtypes: girdleless and girdle and into 6 classes: Primary rings (Archiannnelida), Polychaeta class, Oligochaeta class, Hirudinea class, Echiurida class and Sipunculida class ).
Class Polychaetes (Polychaeta)
From all other annelids, polychaetes are distinguished by a well-defined head section with appendages that perform a sensory function, developed parapodia with setae; dioeciousness, development with metamorphosis.
External building. Polychaetes have an elongated, slightly flattened, cylindrical body, consisting of three sections: the head, trunk and anal lobe - pygidium. The preoral lobe - the prostomium and pygidium do not belong to the segments, since they have a different structure. Prostomium - the head lobe, carries appendages-antennas (lat. Antenna - pes) or tentacles that perform the function of touch and larger palps - palps - perform the function of touch, and also direct food into the mouth and eyes. The second section of the head - the oral segment - the peristomium - is formed from the fusion of 2-3 trunk segments. It is similar to the body segments, but larger, and does not bear parapodia. The mouth and peristomal antennae are located ventrally on this section.
The process of fusion of segments with the formation of a separate head section is called cephalization.
All segments of the body bear skin-muscular outgrowths on the sides - parapodia. Each of them consists of a central, basal part, two lobes depart from it - dorsal and abdominal. Each blade has a thin appendage - the antennae, they perform olfactory and tactile functions. In many polychaetes, the dorsal antennae grows and performs a respiratory function, that is, the function of a gill, provides gas exchange. In addition, each branch of the parapodia bears tufts of setae. Parapodia can perform several functions: sensory organs, locomotor, respiration. Parapodia are best developed in vagrant forms.
The skin-muscle sac consists of a single-layer epithelium, and under it there are two layers of muscle fibers. Outside, the epithelium secretes a thin layer of the cuticle. In the epithelium there are glandular cells, the secret secreted by these cells forms tubules around the body of sessile polychaetes. The outer layer is annular, the inner layer is longitudinal muscles. On the sides there are bundles of fan-shaped muscles that set the parapodia in motion. Crawling polychaetes have the most complex structure skin-muscle sac.
The secondary cavity of the body has several functions: musculoskeletal, transport, homeostatic, excretory. In general, sexual products ripen. Derivatives of the coelom - coelomoducts - serve to bring the reproductive products out.
digestive system consists of an anterior, middle and hindgut. The midgut is of endodermal origin. The foregut is differentiated into the buccal region, pharynx and esophagus. The pharynx is a continuation of the buccal region, has powerful muscles and a narrow lumen. On the border between the buccal region and the pharynx, some species have jaws, which is characteristic of predatory forms. Sedentary ones have a poorly developed pharynx. The pharynx is followed by the esophagus, which opens into the midgut. There are salivary glands in the anterior part of the esophagus. Their upper ducts open into the anterior part of the esophagus. Sometimes there is a small stomach. The midgut has a relatively wide lumen and thinner walls. In it, the final digestion of food and the absorption of nutrients into the blood and tissue fluid occurs, thanks to the powerful vascular plexus around the intestinal wall. The middle intestine sometimes forms paired blind outgrowths - side pockets. In herbivorous individuals, the middle section of the intestine is convoluted. The posterior intestine ends at the anus dorsal side anal lobe.
Respiratory system in different polychaetes it is arranged differently. Some, for example, Nereis, do not have respiratory organs, and gas exchange occurs through the entire surface of the body. Most of the oxygen is taken up by the parapodia, where there is a particularly dense network of blood vessels. Others breathe with gills, which are formed from the dorsal antennae of the parapodia, or from some of the appendages of the head.
Circulatory system the polychaete is closed, that is, the blood circulates only through the blood vessels and does not pour into the body cavity. There are two main blood vessels: dorsal and abdominal. The dorsal blood vessel pulsates, and blood is driven forward through it, the abdominal one does not contract and blood flows backward through it. In each segment, these vessels are connected by an annular vessel. Blood vessels form another series of plexuses. The largest are skin (especially in parapodia), and around the digestive tract.
excretory system polychaetes are represented by nephridia. Their metameric arrangement in each segment of the body in pairs was the reason to call them metanephridia. Each metanephridium begins with a funnel - a nephrostomy, open into the coelomic sac, a convoluted tube departs from the funnel, which penetrates the dissipation and opens outward on the lateral surface of the adjacent segment with a hole - a nephridial pair.
Nervous system consists of two fused cerebral ganglia, which are called supraesophageal, and peripharyngeal connectives. The cerebral ganglia are also called the brain, from which nerve cords run along the body - connectives, in each segment, ganglia are formed on them, connected by commissures. Such a nervous system looks like a ladder and is characteristic of primitive polychaetes. In more highly organized forms, the connectives converge or even merge, just as the ganglia merge. As a result, the nervous system looks like an abdominal nerve chain.
In sessile forms, the sense organs undergo reduction, although some sessile forms have balance organs - statocysts.
reproductive system. Polychaetes reproduce both sexually and asexually. At asexual reproduction the body of the worm is divided into two or more parts. After that, the missing structures are completed. The alternation of these two methods of reproduction (metagenesis) is also observed in polychaetes. Most polychaetes have separate sexes. Sexual dimorphism is not expressed. Sex glands - gonads, are formed in the walls of the coelom. They develop in each segment, and rarely - in the anterior and posterior.
Developing germ cells fall into the whole, where they finish their maturation. Fertilization is external. The exit of germ cells from the body cavity occurs in different ways. In a simple case, the walls of the segments in which the sex cells are located burst, and they end up in the water, and the parental generation dies. Some polychaetes have genital funnels with genital ducts - coelomoducts, and through them the reproductive products are brought out. In the absence of coelomoducts, germ cells are excreted from the coelom through nephromixia, which simultaneously perform the function of the genital and excretory ducts. Fertilization is external, in water. A larva, a trochophore, develops from a fertilized egg.
Further development of the trochophore leads to the transformation of its following larvae: metatrochophore and nektochaete. In the metatrochophore, larval segments are formed in the growth zone. Then the metatrochophore turns into a nektochaete, in which the head ganglion (brain), the abdominal nerve chain is formed. The setae are exposed outward - this is how the parapodial complex is formed.
biological significance The development of rings with metamorphosis lies in the fact that due to floating larvae, species are dispersed, since adults mainly lead a bottom lifestyle. Some polychaetes take care of their offspring, and therefore, their larvae are inactive. There are sometimes live births among polychaetes.
Meaning of polychaete worms:
1. Polychaetes are food for many marine animals.
2. They are among the animal organisms that take part in the purification of sea water.
3. Polychaetes are actively involved in processing organic matter settling at the bottom of the seas.
4. They are an important link in the trophic chains, they serve as objects of acclimatization. So, under the guidance of Academician L.A. Zenkevich in 1939-1940. for the first time in the world acclimatization of polychaetes (Nereis diversicolor) from the Sea of Azov to the Caspian was carried out. Where they successfully took root and improved the food supply, especially for valuable sturgeons.
5. Some polychaetes are used as food, such as the Pacific palolo worm (Eunice viridis).
3. Tasks
Exercise 1. In the figures, consider the external structure of polychaetes, sketch appearance anterior part of the body Nereis pelagica(Zelikman, Fig. 81 A, B), the structure of the parapodia and the posterior end of the body of the polychaete (Zelikman, Fig. 82), study the scheme internal structure polychaete worms (Fig. 1).
Rice. one. Scheme of the internal structure
polychaete worms:
A - nervous and excretory systems (top view),
B - the digestive system and the whole (top view),
B - circulatory, digestive and nervous systems
(side view): 1 - supraesophageal head ganglion, 2 - peripharyngeal connective, 3 - ganglia of the ventral nerve cord, 4 - nerves, 5 - metanephridia, 6 - mouth, 7 - oral cavity, 8 - pharynx,
9 - esophagus, 10 - intestine, 11 - muscles of the pharynx, 12 - whole, 13 - dissipation, 14 - ovary, 15 - dorsal blood vessel, 16 - abdominal blood vessel, 17 - annular blood vessels.
Task 2. Consider the structure of the parapodia of polychaete worms. Examine and in Figure 2 label the notopodium, neuropodia, location of supporting setae (acicles), ventral and dorsal antennae.
Task 4.
Learn, designate and give detailed description the structure of the excretory system of polychaetes and its connection with the whole (Fig. 4).
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Task 4. To study the reproduction and development of polychaetes, and complete Figure 178 (Sharova I.Kh.)
4. Terminology
Architomy -______________________________________________________________
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Atsikula - ___________________________________________________________
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Dissepiments - __________________________________________________________
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Deutocerebrum - __________________________________________________
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Connectives - _________________________________________________________
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Neuropodium - ____________________________________________________________
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Notopodium - ________________________________________________________
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Parapodia - _____________________________________________________________
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Peristomium - __________________________________________________________
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Prostomium - _____________________________________________________
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Whole products - _________________________________________________________
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Palps - _________________________________________________________
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Pygidius - _____________________________________________________________
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Nephromyxium - _____________________________________________________
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5. Issues for discussion
1. What progressive features of organization do polychaetes have in comparison with roundworms and flatworms?
2. What are the features external structure polychaetes?
3. Are the parapodia of polychaetes organs of locomotion? How are they arranged and what function do they perform?
4. What are the circulatory and respiratory system polychaetes? What determines the degree of their development?
5. Why are polychaetes called celiac animals? How is the secondary body cavity different from the primary?
6. What are the features of the structure nervous system polychaetes versus roundworms?
7. What sense organs do polychaetes have and where are they located?
8. What are the similarities and differences digestive system carnivorous and sessile polychaetes?
9. How is the reproductive system of polychaetes arranged? What are the features of their reproduction?
10. What is the structure of the excretory system of polychaetes? Difference between metanephridia and protonephridia.
11. How are the circulatory and respiratory systems of polychaetes interconnected? What determines the degree of their development?