Diversity, significance and general characteristics of coelenterates. Type Coelenterates: general characteristics Diversity and significance of the type Coelenterates
They have an elongated cylindrical body that reaches 1 cm in length. At one end there is a mouth surrounded by 6-12 tentacles, at the opposite end there is a sole, with the help of which the organism attaches to the substrate.
Habitat: freshwater bodies of still water.
Movement - in general, it leads an attached lifestyle, but sometimes it moves due to the contraction of epithelial muscle cells, walking alternately with the sole and with the tentacles.
Feeding - according to the method of obtaining food - a predator, paralyzes prey with substances of stinging cells and pushes it towards the mouth with tentacles. Next, the food enters the intestinal cavity, where it is subject to extracellular and intracellular digestion.
Breathing – absorption of oxygen occurs throughout the entire surface of the body.
The release of metabolic products occurs due to diffusion through the surface of the body.
Response to stimuli - characterized by simple, monotonous reflexes that manifest themselves in contraction of the body in response to the action of mechanical or chemical stimuli.
Irritation is perceived by nerve cells, quickly leads to excitation of the entire nervous system, and from it is transmitted to epithelial muscle cells, causing their instant contraction. In response to the touch of living organisms, stinging cells are activated.
Their cytoplasm contains a capsule with a stinging filament, and the outer membrane has a sensitive hair. Even with a slight touch to this hair, the stinging threads are thrown out and dig into the body of the victim, where a paralyzing substance enters from the capsule along the thread.
Reproduction - budding occurs in the warm season.
First, a protrusion of a double layer forms on the body, over time new tentacles and a mouth opening are formed on it, and the young individual is separated from the mother’s body.
Sexual reproduction usually occurs in the fall. The gonads are formed from ectoderm cells; gametes are formed in them, which are released outward, where they are fertilized. Hermaphrodite; eggs mature later than sperm, preventing self-fertilization. After several divisions of the zygote, a resting stage begins, the embryo becomes covered with membranes and overwinters.
Class diversity - there are single and colonial forms, marine or freshwater. Colonies are formed due to the fact that new individuals do not separate from the mother organism.
Class scyphoid (jellyfish)
The body has the shape of an umbrella, and consists of stems and a crown, the diameter of which ranges from 2-3 cm to 2 m (aurelia). At the edges of the umbrella there are numerous tentacles that can reach 30 m in length (aurelia). The body is gelatinous due to the large amount of water (up to 98%) contained in the mesoglia.
The habitat is exclusively marine.
Movements are freely mobile. The movement is ensured by the contraction of the muscle cells of the crown and the sharp expulsion of water from the intestinal cavity (reactive movement).
Reacting to stimuli - reflexes - is somewhat difficult, since the nervous system is a collection of nerve cells, similar to ganglia. They have light-sensitive eyes and balance organs. Stinging cells are located mainly along the edges of the dome and on the tentacles.
Reproduction is characterized by a change in sexual (jellyfish) and asexual (polyps) generations and indirect development of the embryo.
Life cycle of scyphoid jellyfish (Aurelia)
Dioecious jellyfish produce gametes in special genital organs, which are located in the Endoderm. Gametes are excreted through the mouth, fertilization is external.
A mobile larva develops from a fertilized egg, which eventually attaches to the substrate and grows into a polyp. It increases in size and vegetatively forms new jellyfish. The polyp stage does not last long.
Diversity of the class - there are about 200 species.
There are species that are seriously dangerous to humans. For example, after touching the cornerota jellyfish, which lives in the Black and Azov Seas, a burn remains on the skin. Some types of tropical jellyfish are called “crystal meat” and are eaten in China and Japan.
Class Coral polyps
Most form colonies, but there are also individual forms (anemones). Dimensions range from a few millimeters to tens of centimeters. Characterized by the formation of a solid external or internal skeleton of limestone and horny substances.
Habitat - exclusively marine environment, mainly warm shallow waters.
Locomotion - they lead an exclusively attached lifestyle, but well-developed muscle fibers allow them to change the shape of the body.
Diet: They feed on small fish, worms, and crustaceans. The digestive cavity is divided into numerous chambers, due to which its surface increases.
Response to stimuli – the nervous system is of a diffuse type, most of the nerve cells are located near the mouth.
Reproduction is budding or longitudinal division of a polyp. Sexual reproduction occurs in the following stages: maturation of gametes; fertilization of eggs in the digestive cavity, where sperm enter with a stream of water; the formation of a larva from a fertilized egg, which is brought out through the mouth, settles to the bottom and gives rise to a new polyp. There is no alternation of generations.
Diversity class - the largest group of coelenterates, has about 6 thousand species.
The calcareous skeletons of coral polyps form reefs and oceanic islands, which are home to a huge number of animals.
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Lesson topic: “The diversity and importance of coelenterates”
Target : Reveal the diversity of coelenterates, features of their structure and lifestyle, connection with the environment, significance in nature and human life.
Equipment: drawings, film fragment, table “Type Coelenterates”, physical map of the world
Type : combined
During the classes
Organizing time
Updating knowledge
Guys! In the last lessons we became acquainted with the coelenterates - the most poorly organized of the true multicellular animals.
What two life forms are distinguished among the coelenterates?
Why do these animals belong to the same type? Why are they called coelenterates?
Are these statements true?
(Not really)?
Coelenterates belong to the subkingdom Protozoa. (no)
Coelenterates belong to the subkingdom Multicellular. (yes)
They have bilateral body symmetry. (no)
They have radial symmetry of the body. (Yes)
Exclusively aquatic animals (yes)
Among the coelenterates there are terrestrial species. (no)
Double layered animals (yeah)
Three-layer animals. (No)
Have ectoderm, endoderm and non-cellular mesoglea (yes)
In these organisms, a diffuse type nervous system appears for the first time. (Yes)
In these organisms, a ladder-type nervous system appears for the first time. (No)
These organisms have a respiratory system for the first time (no)
Have an intestinal cavity (yes)
They only have a mouth opening. (Yes)
There is a mouth and anus (no)
For the first time, coelenterate digestion appeared. (yes)
Intracellular digestion preserved (yes)
Characterized by the presence of stinging cells (yes)
Among the coelenterates there are colonial forms (yes)
Most are characterized by two main life forms: polyp and jellyfish (yes)
Learning a new topic
Guys! You and I have learned so much about coelenterates. What haven’t we covered that you still want to know?
What do you think, what if other representatives of the type are coelenterates?
Coelenterates are the most ancient of the true multicellular animals. This is evidenced by the simplicity of their structure, which is manifested in a small variety of cells of the two-layer body, as well as a high ability to regenerate. Scientists have proven that coelenterates descended from some of the first multicellular animals, whose bodies had two types of cells: motor cells with flagella and digestive cells with pseudopods. These ancestors of coelenterates evolved from colonial single-celled animals similar to the colonies of living flagellates.
What is the evidence for the origin of coelenterates from ancient colonial animals?
1. The development of modern multicellular animals (including coelenterates) comes from one cell (fertilized egg).
2. Digestive cells of hydra have flagella and pseudopods.
3. Hydra sex cells are similar in shape to unicellular organisms: the egg is like an amoeba, the sperm is like a flagellate.
Ancestors of coelenterates
True coelenterates
A multicellular animal with two types of cells: 1) motor with flagella, 2) digestive with pseudopods
Digestive cells of hydra have flagella and pseudopods
Descended from colonial unicellular organisms
Development from one cell - a fertilized egg
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Populated the entire ocean, even the polar regions and tropics
Over the long history of the development of this type, its representatives have managed to adapt very well to a wide variety of living conditions. They populated literally the entire ocean from its surface to the extreme depths; they can be found in the polar regions and in the tropics.
Coelenterates settle on a wide variety of soils, some of them are able to withstand significant changes in the salinity of sea water, and some species have even penetrated into fresh waters. Almost everywhere they play an important role in the formation of communities of marine animals and plants. Let's get to know these interesting creatures better. To make it easier to understand the systematic position of individual species of coelenterates, we will create a brief system like
Work based on textbook materials (§14)
Make a classification of the type and write down representatives of the classes.
Compile and record in a table the characteristics of the classes of coelenterates
Hydroid class
Class scyphoid
Class coral polyps
Habitat
Live in the sea, several freshwater forms
Exclusively marine organisms
The structure of the intestinal cavity
The intestinal cavity is devoid of radial septa
The intestinal cavity has incomplete radial septa
The intestinal cavity is divided into chambers by radial partitions
Development of the gonads
Gonads develop in the ectoderm
Gonads develop in the endoderm
The gonads develop in the endoderm.
There is no jellyfish stage in development
Hydroids have the simplest structure among coelenterates. Ancient hydroids gave rise to coral polyps and scyphoid coelenterates.
Our diagram shows only the division of coelenterates into three classes and says practically nothing about their great diversity. In order to get acquainted with the diversity of coelenterates and their significance in nature and human life, we will travel around the world. Of course, only in absentia! And so that we can accurately imagine where we are, we will use a geographical map of the world on which we will mark stops. And you are all participants in a scientific expedition, and as in any expedition, it is necessary to record everything new and significant.
To work on a geographical map, you can use dynamic elements - figures of coelenterates attached to pins. Then the student will not only show the location of the seaplane, but also mark the habitats of certain animals using labels. Students are encouraged to create questions and note meanings in nature and human life as they travel.
- Who dreams of traveling around the world? Hurry! Now we are setting sail across the seas and oceans. Our seaplane is already on its way. We are approaching the shores of Australia. But what is it? We found ourselves in underwater thickets. The quietest move! Coral reefs! They very often interfere with shipping. And before they were the cause of a shipwreck (fragment of the film).
The variety of structures created by corals can be divided into several main types. There are coastal reefs located directly along the shores of islands or continents, barrier reefs receding from the coast at some distance, and atolls - ring-shaped coral islands. It has not yet been possible to calculate the total number of atolls. There are 1,190 of them in the Maldives alone.
The largest structure built by tiny craftsmen is the Great Barrier Reef. It stretches for 2000 km along the northeast coast of Australia. Its width is up to 150, and its height is 2 km. Apparently, the sea in this area was shallow, and then the bottom sank, but this happened so slowly that the reef had time to grow. The total area of all known reefs is 27 million square kilometers, of which 8 million are islands. They could make a continent slightly larger than Australia.
Well, let's sail on. Do you know which sea is the bluest? Well, of course the Mediterranean. Is there anything interesting here for us? Eat! Stop the car! What are these people doing in the boats? They lower into the water some complex and clumsy devices, either made of sticks or bamboo. For what? No one knows? Message 1. Red coral.
While we were listening to the story about the noble coral, our sailor ended up in the Black Sea. Guys, look how many coelenterate animals there are here. Some of them are decorations of the underwater landscape, and without them it is impossible to imagine the fauna of the Black Sea. Underwater you notice a large number of jellyfish. Message 2. Jellyfish.
It has long been noticed that some animals sense the approach of a storm long before it begins: whales go far into the sea, seagulls rush in the air, and jellyfish hide in the depths. This interested scientists. It was found that when a storm occurs, air vibrations arise from friction against the crests of storm waves; the frequency of these vibrations is 8–13 times per second. Apparently the jellyfish hears the voice of the sea and hides. Engineer B. S. Ivanov and doctor G. Novinsky became interested in whether it was possible to build a storm prediction device on this basis. It turned out that the auditory cavity can either shrink or unclench, tuning into resonance with the voice of the sea. Using a hint from nature, the inventors designed an electronic device - a storm harbinger. It helps to know about the approach of a storm 12 hours in advance and can predict thunderstorms, squalls, typhoons and hurricanes.
The last point of our voyage is the Far Eastern seas.
Message 3. Siphonophores.
Our voyage has come to an end. We visited many places and learned quite a lot of interesting things about coelenterates. They live mainly in the seas, are very diverse in appearance, shape, way of life, and are often brightly and colorfully colored.
Generalization, conclusions.
Working with the text of the textbook and notes in notebooks, students must form a conclusion about the great role of coelenterates in nature and human life.
Guys! What do you remember most, what did you pay attention to? What conclusion do we draw?
1) Predators. They feed on small animals - fish, crustaceans, and regulate their numbers in nature; are a component of the food chains of marine communities
2) Symbiote
3) Madrepore corals create reefs. Together with plants they form unique communities - coral reef communities
4) Red coral skeleton is used to make jewelry and souvenirs
5) Coral reefs interfere with shipping
6) Skeletons of colonial coral polyps are used to obtain lime and are used in construction
7) Can serve as laboratory animals
8) May cause poisoning
4.Homework
5.Assess students
Ministry of Education of the Republic of Bashkortostan
City Department of Education
Teacher certification materials
Biology and Geography Municipal Educational Institution "Secondary School No. 1"
Simonova Nelly Salavatovna
Sibay 2007
Despite the rather simple structural features, the importance of coelenterates in nature is very noticeable. And the total number of representatives of this type reaches 10 thousand species. Their habitats are also diverse - from small fresh water bodies to deep ocean depressions. We will briefly consider the importance of coelenterates in nature in our article.
origin of name
It is no coincidence that these multicellular animals have such a taxonomic unit name. The fact is that they have an intestinal cavity in which food is digested. It enters it through the mouth opening with the help of tentacles. Specialized ones secrete digestive enzymes into the body cavity, under the influence of which the digestion process occurs.
Character traits
The importance of coelenterates in nature and human life is largely determined by the features of their structure. First of all, these are two layers of the body: outer and inner. They consist of specialized cells. Each type performs specific functions. During division, intermediate cells give rise to new cells; nerve cells unite the body into a single whole and determine its relationship with the environment. And thanks to the presence of skin-muscle cells, coelenterates can compress, bend and move.
The “calling card” of coelenterates is They are located in the outer layer of the body. These cells consist of a capsule, inside of which there is a twisted thread with a sharp end. A sensitive hair is located outside the cell. When an individual touches someone, the stinging thread unwinds and bites forcefully into the victim’s body. At the same time, a toxic substance is introduced. It can not only paralyze, but also lead to the death of the body.
Freshwater hydra
The importance of coelenterates in nature and for humans can be considered using the example of their typical representative - hydra. This small organism is a link in the food chain. Of course, they are inaccessible to fish fry, since they are burned by stinging cells. But for cladocerans their effect is not terrible, so they feed on the tissues of this species of coelenterates. The surface of the body of hydras is ideal for habitat of different types of ciliates.
The discovery and study of features was an important stage in the development of taxonomy. Experiments involving this organism were proof that regeneration and inability to engage in sexual activity are not their distinguishing features. The name hydra was given by the founder of taxonomy, Carl Linnaeus. He was referring to the mythological character of the same name, who quickly regenerated severed heads. Freshwater hydra also amazes with its ability to regenerate. It can completely recover from 1/200th of it!
Hydra purifies water from organic particles, being a natural filter.
Dangerous burns
We looked a little at the importance of coelenterates in nature. Every person who has experienced the effects of jellyfish stinging cells should be interested in this topic. They are located on the surface of their bell and oral cavities. Encountering many of these organisms can be unsafe.
Colonies live in tropical seas. The poison of their stinging cells causes severe burns, pain, and disturbances in the rhythm of breathing and heart function in humans. If help is not provided to the victim in time, the outcome can be fatal. The inhabitants of the northern areas are just as dangerous: the cyanide.
In case of severe burns, it is necessary to remove stinging cells from the skin using a cloth and treat the affected area with ammonia, alcohol or soda solution. If the exposure was severe, you should immediately consult a doctor.
Jellyfish
Translucent umbrellas of jellyfish, unlike polyps, are able to actively move. They are typical predators, hunting invertebrate animals and fish. Some are capable of jet propulsion. Others, for example, the sea lantern and others, slowly crawl from place to place.
What is the significance in nature of coelenterates leading an active lifestyle? Naturally, it is an important and essential component of marine ecosystems and food chains.
In addition to poisonous species, edible ones are also known in nature. In many Asian countries they are a favorite delicacy.
Like hydras, jellyfish are objects of experimental zoology. And the device, capable of predicting earthquakes, storms and storms, is designed based on the structure of these marine inhabitants.
Corals
The significance of coelenterates in nature is also interesting to consider using the example of colonial coral polyps. In appearance, they do not at all resemble animals, especially since they lead an attached lifestyle. When reproducing by budding, the resulting protrusions are not split off. As a result, strangely shaped structures are obtained. Their internal skeleton is formed by calcium carbonate or solid organic matter.
The coral anemone polyp looks like a bright fantastic flower. Most of them lead a predatory lifestyle, hunting small mollusks, crustaceans and fish. There are also filter feeders. Such sea anemones feed on algae, bacteria and protozoa in the water. At the same time, they also perform an additional function - they purify water.
underwater house
The hermit crab knows exactly what importance coelenterates have in nature. And this is not really a joke. The thing is that without this polyp, cancer simply cannot exist. The sea anemone, in turn, receives the leftover food from the crayfish and uses it as a means of transportation. By changing the shell, the animal transplants its own polyp onto it. And in the literal sense of the word. He strokes the sea anemone with his claws so that it crawls to a new place. This is such an amazing mutually beneficial “cohabitation”.
Warning: reefs
Coral reefs are of particular importance in the nature of coelenterates. These are large colonies of polyps, the number of individuals in which reaches millions. The largest of them is the Great Barrier Reef, which stretches along the Australian Pacific coast.
This natural formation is home to many species of algae, crustaceans, mollusks, worms and fish. In coastal tropical island countries, people collect edible marine plants and animals from the reefs. And limestone obtained from reef skeletons is used in construction. Since corals are formed from a very hard substance, they protect the shores of continents and islands from erosion. Due to their aesthetic appeal, they are used to make jewelry, household items, and souvenirs. Many researchers believe that life on small tropical islands without reefs would be simply impossible. It's all about the high biological productivity of this natural underwater ecosystem, the reasons for which scientists have yet to figure out.
Due to their unique structural features and species diversity, the importance of coelenterates in nature is quite important and determines their significant role in the natural ecosystems of the planet.
One of the first groups of multicellular animals is the type Coelenterata. Grade 7, which includes a zoology course, examines in detail all the structural features of these amazing creatures. Let's remember once again what they are.
Type Coelenterates: biology
These animals received the name of the systematic unit due to the structure of the same name. It is called the intestinal cavity, and all representatives of the type have it: both polyps that lead an attached lifestyle and actively moving jellyfish. A characteristic of the coelenterate type is also the presence of specialized cells. But despite such a progressive structural feature, the body of these animals does not form real tissues.
Habitat and size
These first true multicellular animals can be found in fresh and salt water bodies of various climatic zones. The type Coelenterates (the 7th grade of a comprehensive school studies this topic in some detail) is represented by small individuals with a diameter of several millimeters, and giant jellyfish with tentacles up to 15 meters long. Therefore, the nature of the reservoir where they live may be different. Thus, small freshwater hydras live in small puddles, and coral polyps form huge colonies in tropical seas.
Type Coelenterates: general characteristics
The body of all coelenterates consists of several types of cells, each of which performs a specific function, like the organs of more complex animals.
The main characteristic of coelenterates is the presence. They consist of a capsule in which a thread with a sharp end is twisted. A sensitive hair is located on top of the cell. When it touches the victim's body, it spins and bites into it with force. As a result, it has a paralyzing effect. Next, using tentacles, representatives of this type place the victim into the intestinal cavity. And here the process of breakdown of organic substances begins. And the digestive and
The Coelenterate type is characterized by a high degree of regeneration. Scientists have proven that freshwater hydra can completely restore a body from 1/200 parts. And this is possible due to the presence of intermediate cells. They actively divide, giving rise to all other types. Coelenterates are also capable of sexual reproduction due to the fusion of eggs and sperm.
Nerve cells are scattered throughout the body, interconnecting the body with the environment and uniting it into a single whole. So, the movement of one of them is very interesting - the hydra. Thanks to the activity of the skin-muscle cells, she, like an acrobat, moves from the head to the sole, doing a real somersault.
Life processes of coelenterates
The phylum Coelenterata is characterized by a more complex physiology compared to its predecessors - protozoa and sponges. Although there are some common signs. For example, gas exchange still occurs through the integument, and there are no specialized structures for this.
Due to the presence of skin-muscle cells, jellyfish are capable of contracting. At the same time, their bell contracts, water is pushed out with force, causing a reverse push.
All coelenterates are carnivorous animals. With the help of tentacles, prey enters the body through the mouth opening. The effectiveness of the digestion process is proven by the simultaneous existence of two types of digestion: cavity and cellular.
Coelenterates are characterized by the presence of a response from their body to irritation - reflexes. They arise in response to mechanical or chemical influences from the environment. And jellyfish have special sensitive formations that ensure the maintenance of body balance and perception of light.
Life cycle
The phylum Coelenterata is also characterized by the fact that in many of its species there is an alternation of generations in the life cycle. For example, the aurelia polyp reproduces exclusively asexually using budding. Over time, the body of one of them is separated by transverse constrictions. As a result, small jellyfish appear. Visually, they resemble a stack of plates. One by one, they break away from above and move on to an independent and active lifestyle.
The alternation of sexual and asexual generations in the life cycle of coelenterates contributes to a rapid increase in their numbers and more efficient settlement.
Includes the type Coelenterate classes, the polyps of which are not shed off. They form colonies of bizarre shapes. These are coral polyps. There is no alternation of generations in freshwater hydra either. They reproduce in the summer by budding, and in the fall they proceed to sexual reproduction, after which they die. Fertilized eggs overwinter at the bottom of reservoirs. And in the spring, young hydras develop from them.
Diversity of coelenterates
The phylum Coelenterates in nature is represented by two life forms: polyps and jellyfish. One of the most interesting representatives of the first group is sea anemone. This is an inhabitant of warm tropical seas, which, thanks to its bright color, looks like a fantastic flower. Hence the second name for sea anemones - sea anemones. Among them there are predators and filter feeders. And some species of sea anemones can enter into mutually beneficial cohabitation with hermit crabs.
The polyp has the ability to move and feed on the remains of organic arthropod food. And the cancer is reliably protected by the stinging cells of the sea anemone. It is interesting that, changing the shell from time to time, he also transplants the polyp there. The cancer strokes the sea anemone with its claws, as a result of which it independently crawls to a new home.
And colonies of coral polyps form huge clusters. For example, the Great Barrier Reef stretches along the coast of Australia for a distance of about 2 thousand km.
The importance of coelenterates in nature and human life
Many coelenterates can be dangerous to animals and humans. The action of their stinging cells causes burns. Their consequences for humans can be convulsions, headaches, disturbances in the functioning of the heart and respiratory organs. If help is not provided in time, death is possible.
Polyps and jellyfish are an important link in the food chain of aquatic life. And corals in many countries are used to make jewelry, souvenirs and building materials.
So, the type Coelenterates, the general characteristics of which we have considered, is represented by two life forms. These are polyps and jellyfish. These animals are characterized by the presence of specialized cells and alternating generations in the life cycle.
Diversity of coelenterates
S.V. Naidenko
Coelenterata (Coelenterata or Cnidaria) are classified as a separate phylum of animals; there are about 9,000 species. They are characterized by radial symmetry: they have one main longitudinal axis, around which various organs are located in a radial order. In this they differ sharply from bilaterally symmetrical (or bilateral) animals, which have only one plane of symmetry, dividing the body into two mirror-like halves - right and left.
All radially symmetrical animals lead a sedentary lifestyle or led it in the past, i.e. originate from attached organisms. One of the poles of the body serves to attach the animal to the substrate; at the other end there is a mouth opening. Coelenterates are two-layered animals; during ontogenesis, they develop only two germ layers - ectoderm and endoderm. Between the outer and inner layers there is a non-cellular substance, sometimes it forms a thin layer (hydra), sometimes a thick gelatinous layer (jellyfish). The body of coelenterates has the appearance of a sac, open at one end. Digestion occurs in the cavity of the bag, and the hole serves as a mouth, through which undigested food remains are removed.
However, this is a generalized diagram of the structure of coelenterates, which may change depending on the lifestyle of specific representatives. The sessile forms of coelenterates - polyps - most closely correspond to this description. Freely moving jellyfish are characterized by flattening of the body along the longitudinal axis. The division into jellyfish and polyps is not systematic, but purely morphological; sometimes the same species of coelenterates at different stages of the life cycle can look like either a polyp or a jellyfish.
Another characteristic feature of coelenterates is the presence of stinging cells.
The phylum is divided into three classes: hydrozoa (Hydrozoa, about 3000 species), scyphozoa (Scyphozoa, 200 species) and coral polyps (Anthozoa, 6000 species). Each class has well-known representatives.
Among the hydrozoans, this is a small (up to 1 cm) hydra polyp, found in our fresh water bodies. It leads a sessile lifestyle, attaching itself to the substrate with its base, or sole. At the free end of the body there is a mouth opening, surrounded by a corolla of 6-12 tentacles, on which the bulk of the stinging cells are located. Hydra feeds mainly on small crustaceans - daphnia and cyclops. Reproduction occurs both sexually and asexually. In the first case, a new hydra develops from a fertilized egg after a certain period of rest (winter).
It should be noted that most hydroid polyps, unlike hydra, lead not a solitary, but a colonial lifestyle. At the same time, in such colonies special mobile individuals arise and bud off - the same jellyfish that are responsible for the settlement of polyps. Jellyfish actively move and release mature germ cells into the environment. The larva that has developed from a fertilized egg also moves in the water column for some time, and then sinks to the bottom and forms a new colony.
As a separate subclass in the hydroid class, siphonophora are distinguished, which include very interesting colonial animals from the genus Physalia. These are marine organisms that live mainly in the southern seas.
Although outwardly the physalia looks like a solitary animal, in fact, each of it is precisely a colony of organisms. In it, individual individuals are attached to a single trunk, in which a common gastric cavity is formed, communicating with the gastric cavity of each individual. The upper end of the trunk is swollen, this swelling is called an air bubble or sail, and represents one highly modified medusoid individual. Along the edges of the hole leading into the cavity of the bladder, a closing muscle is formed: the bladder or by releasing gas from it (it is secreted by the glandular cells of the bladder, its composition is close to air), the physalia are able to float to the surface or sink into the depths. Below the bladder are others specialized in feeding or reproduction, as well as stinging polyps.
In physalia, there are two main types of arrangement of the mass of tentacles of the colony under the bladder: shifted to the left or shifted to the right. This allows the colonies, moving along the surface of the water under the influence of the wind, to move in two different directions and to some extent protects them from the fact that in some unfavorable direction of the wind they will all be thrown onto the shore shallows at once.
In one of the most common physalia of the Pacific Ocean (Physalia utriculus), one of the tentacles, the so-called lasso, is longer than all the others and can reach 13 meters or more in length. Along it are located thousands of stinging batteries, each of which consists of hundreds of microscopic capsules (individual cells) called nematocysts. These spherical cells contain a tightly wound, hollow, drill-shaped thread that conducts the venom. When a fish encounters a tentacle, the threads pierce the tissues of the victim, and the poison from the capsules is pumped through these channels. Thus, the lasso captures and paralyzes the prey, and then pulls it towards the mouth.
If the physalia stings a person who accidentally touches it, the consequences can be very serious. Physalia burns are very painful, blisters appear on the victim’s skin, lymph glands become enlarged, sweating increases, and nausea appears. Sometimes victims find it difficult to breathe.
A close relative of the physalia, the Portuguese man-of-war (Physalia physalis), has long been known. Its crested float, approximately 35 cm long, is very colorful - the membrane is iridescent blue, turning into mauve and then, at the top of the crest, into pink. The ship's colonies look like unusually elegant balls, often drifting intact on the surface of the ocean. From time to time, the boat dips the float in water so that the membrane does not dry out. Deadly poisonous tentacles stretch 10-15 m down from the float, capable of paralyzing large fish and pulling them up to the digestive organs. Although physalia are inhabitants of the open ocean, many of them, under appropriate currents and weather conditions, are carried to the shores of Northwestern Europe. Even washed ashore, they retain the ability to sting anyone who touches them.
The optimal way to interact with physalia for a person at sea is to try to get away or swim away from them, remembering that dangerous tentacles more than 10 m long are attached to a small air bubble below.
Despite the toxicity of physalia, some sea turtles eat them in huge quantities. People, of course, do not eat physalia, but they also find uses for them. Farmers in Guadeloupe (Caribbean) and Colombia use dried physalia tentacles as rat poison.
In scyphoid jellyfish, the body has the shape of a rounded umbrella with long tentacles suspended from below. In all species, a gastrovascular system of varying complexity is formed with radial canals running from the stomach to the edges of the body. A number of tentacles in jellyfish are modified, turning into so-called marginal bodies. Each of these bodies carries one statocyst (a formation involved in maintaining balance) and several ocelli, including some of a very complex structure. The body of most jellyfish is transparent, which is due to the high (often up to 97.5%) water content in the tissues. Certain species of scyphoids, such as the eared jellyfish (Aurelia aurita), known to everyone who has visited the Black Sea, are very widespread - in almost all seas.
Coral polyps generally resemble hydroid coelenterates, but their structure is much more complex. They have differentiation of muscle tissue, and many have skeletal formations. Madrepore, or reef-building corals (from the group of six-rayed corals, Hexacorallia)* have branches that sometimes reach 4 m in length. They are what form coral reefs.
The red noble coral of the Mediterranean Sea (Corallium rubrum) belongs to the eight-rayed corals (Octocorallia) and is not capable of forming reefs. Its colonies grow on the coastal slopes of the Mediterranean Sea at a depth of more than 20 m (usually from 50 to 150 m). The history of the name is interesting. It comes from the Greek word for a hook used by divers to extract coral from great depths. In much the same way, noble red coral, which has long been used for making jewelry, is mined today.
With all the diversity of corals, the polyps, which, in fact, make up the colonies, are arranged more or less the same way. An individual polyp, located in a calcareous cell, is a tiny living lump of protoplasm with a complex internal structure. The polyp's mouth is surrounded by one or more tentacle corollas. The mouth goes into the pharynx, and it goes into the intestinal cavity. One of the edges of the mouth and pharynx is covered with large cilia that drive water into the polyp. The internal cavity is divided into chambers by incomplete partitions (septa). The number of partitions is equal to the number of tentacles. The septa also have cilia that drive water in the opposite direction - from the cavity to the outside.
The skeleton of madrepore corals is quite complex. It is built by the cells of the outer layer (ectoderm) of the polyp. At first, the skeleton looks like a small cup in which the polyp itself sits. Then, as radial partitions grow and form, the living organism finds itself, as it were, impaled on its skeleton.
Coral colonies are formed by budding. Some corals have not one, but two or three polyps in each cell. In this case, the cell stretches out, becomes like a rook, and the mouths are arranged in one row, surrounded by a common rim of tentacles. In other species, dozens of polyps are already sitting in the limestone house. Finally, in meanderine corals, all polyps merge to form a single organism. The colony takes on the appearance of a hemisphere covered with numerous winding grooves. Such corals are called brain corals; the grooves on them are fused mouth slits lined with rows of tentacles.
Colonies of coral polyps grow quite quickly - branched forms, under favorable conditions, grow up to 20-30 cm per year. Having reached low tide, the tops of coral reefs stop growing and die, and the entire colony continues to grow from the sides. New colonies can grow from broken branches.
Corals also have sexual reproduction; these organisms are dioecious. A free-swimming larva is formed from a fertilized egg, which after several days settles to the bottom and gives rise to a new colony.
In order for coral polyps to grow calmly and build reefs, they need certain conditions. In shallow, well-heated lagoons, they can withstand water heating up to 35 °C and a certain increase in salinity. However, cooling water below 20.5 °C and even short-term desalination have a detrimental effect on them. Therefore, in cold and temperate waters, as well as where large rivers flow into the sea, coral reefs do not develop.
