Their characteristic appearance is given by a convex umbrella and massive oral lobes with numerous processes. Unlike other scyphoids, corneros jellyfish lack a corolla of tentacles located along the edge of the umbrella. About 80 species are known. Some representatives (for example, Nemopilema nomurai) during outbreaks of numbers can create difficulties for fishing.
| Cornerots | ||||||||||
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| Stomolophus meleagris |
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Rhizostomeae Cuvier, |
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Reproduction and life cycle
The usual life cycle of rootmouths is metagenesis - alternation of asexual generation (polyps) and sexual generation (jellyfish).
Cornerosteal polyps ( scyphistomas) have a goblet shape, small size and lead a bottom-dwelling lifestyle. Their reproduction is carried out by lateral budding (in this case other polyps are formed) or by strobilation, as a result of which planktonic stages are formed - ethers, which subsequently develop into jellyfish.
Jellyfish can reach significantly larger sizes (over 2 m in diameter) and for most representatives they live in the water column. As a result of external insemination, a planula larva is formed from the egg, which settles to the bottom and transforms into a scyphistoma.
Jellyfish
Structure
The primary mouth opening of most corneros jellyfish becomes overgrown. Inside the umbrella there is a voluminous stomach, devoid of septa, at the bottom of which there are four gonads. A dense irregular network of thin gastrovascular canals extends from the stomach cavity, which penetrate the entire umbrella and enter the oral lobes. In forms lacking a primary mouth, the canals of the oral lobes break out and form numerous secondary oral openings.
The oral lobes, which in many cornerotes are fused into a single formation, have a characteristic process structure, which gives the order its name. Their epidermis is rich in stinging cells, with the help of which the rootmouths immobilize the victim. The hunting tentacles along the edge of the umbrella, which are common for other jellyfish, are absent.
Lifestyle
The main source of food is planktonic organisms, which jellyfish catch from the jet stream that occurs when the umbrella contracts and swallow through secondary oral openings on the oral lobes. There is evidence that rootmouths are capable of external digestion, due to which they are able to feed on larger organisms, for example, fish.
Movement
Externally, the “hands” resemble the roots and stems of sea plants. Hence its unusual name - cornerot. There are no tentacles at all. Cornerota jellyfish are excellent swimmers. Unlike their relatives, they can move in any direction.
Answers to test questions in biology chapter No. 2 Type Coelenterates
Complete the sentences.
The type Coelenterates has 10 thousand species.
Representatives of the Coelenterate type are inhabitants of both fresh and sea water bodies.
Representatives of the Coelenterate type are characterized by radial symmetry of the body.
The structure of a freshwater hydra polyp
- Oral opening
- intestinal cavity
- outer slot
- tentacles
- inner layer
- sole
Look at the drawing. Where is the well-fed and where is the hungry hydra depicted? Explain your decision.
A hungry hydra has its tentacles retracted.
A well-fed hydra has its tentacles spread out.
Match the species of coelenterates with their belonging to the class of hydrozoans, scyphoid jellyfish or coral polyps.
- Aurelia
- Cornerot
- Kraspedakusta
- sea anemone
- Cross
- Physalia
- Noble coral
- Hydra
A - 8
B - 1, 2, 3, 5, 6
B - 4, 7
Match the names of the types of cells in the body of freshwater hydra with their functions.
| 1 | 2 | 3 | 4 | 5 | 6 |
| V | e | b | G | d | A |
The figure shows a diagram of sexual reproduction and development of freshwater hydra. Read the material on p. 14 of the textbook and, based on it, make symbols in the figure.
- egg
- sperm
- zygote
4-6 - stages of development of the hydra embryo; 7 - young individual
Consider a schematic drawing of a section of a scyphoid jellyfish. Make the designations based on the fact that all coelenterates have the same structural principle.
- tentacles
- nerve rings
- oral stalk
- oral lobes
- mouth opening
- intestinal cavity
- surface layer
- inner layer
- gelatinous layer
- radial channel
It is known that corals do not live at a depth of more than 50 m. What do you think this might be connected with?
They lead an attached lifestyle and need a lot of light and warmth.
Give one of the important evidence of the origin of coelenterates from protists.
Presence of intracellular digestion.
There is a known phenomenon when a hermit crab, having found an empty shell with an anemone settled on it, abandons its old house and takes over the shell with the anemone. How does cancer benefit from sea anemone? Why does sea anemone settle on the shell of a hermit crab?
Sea anemone protects the crayfish and feeds on the remains of its food.
Test tasks for self-control
- The intestinal cavity of the freshwater hydra communicates with the external environment:
a) only by mouth;
b) mouth and anus;
c) pores;
d) only the anus.
- Between the outer and inner layers of cells of the hydra body is located:
a) intestinal cavity;
b) nervous system;
c) dense supporting plate;
d) intermediate cells.
- Which of the hydra body cells are not part of the outer layer?
a) Ferrous;
b) stinging;
c) nervous;
d) reserve;
e) pigmented;
e) dermal-muscular.
- Which of the cells of the hydra's body are not part of the inner layer?
a) Digestive;
b) pigmented;
c) stinging;
d) reserve.
- The stinging cells of the hydra are located:
a) only on the tentacles;
b) around the mouth;
c) on the entire surface of the body;
d) on the sole.
- Hydra is characterized by digestion:
a) intracellular;
b) cavity;
c) extraintestinal;
d) a combination of intracellular and cavity.
- Hydra is characterized by reproduction:
a) asexual - budding throughout life;
b) only sexual;
c) budding - in the summer and sexual - at the end of summer;
d) sexual - in spring and summer, budding - in autumn.
- A representative of coral polyps is:
a) sea anemone;
b) corner mouth;
c) cyanide;
d) hydra.
- Which jellyfish is not dangerous to humans?
a) Kornerot (crystal meat);
b) kraspedakusta;
c) cross;
d) physalia;
e) aurelia (eared jellyfish).
Corner jellyfish (Rhizostoma pulmo) is the largest jellyfish in the Black and Mediterranean seas. Jellyfish belongs to the order Cornerota (lat. Rhizostomeae) and can reach 50-60 cm in diameter and weigh 10 kg.
This pelagic species is widely distributed in the Atlantic Ocean, the eastern Mediterranean Sea (especially along the Adriatic coast) and the Black Sea.
A convex umbrella and massive oral lobes with numerous processes give the jellyfish a characteristic appearance. Poisonous stinging cells are located on the lacy blades. The venom of Rhizostoma pulmo does not pose a serious danger to humans. Only in sensitive people, upon contact with the oral blades, severe irritation may occur, similar to a nettle sting, which disappears within a short time. This is probably why the jellyfish is also called sea nettle, zhigalka, and stinging nettle.
The usual life cycle of rootmouths is metagenesis - alternation of asexual generation (polyps) and sexual generation (jellyfish).
Corneros polyps (scyphistomas) are goblet-shaped, small in size and lead a bottom-dwelling lifestyle. Their reproduction is carried out by lateral budding (in this case other polyps are formed) or by strobilation, as a result of which planktonic stages are formed - ethers, which subsequently develop into jellyfish.
As a result of external insemination, a planula larva is formed from the egg, which settles to the bottom and transforms into a scyphistoma.
The jellyfish's umbrella is constantly contracting, and the animal actively moves, taking any position, but most often swims on its side. When the cornermouth wants to leave the surface, it does not stop moving, as other jellyfish do in order to calmly drown, but turns its dome down and, continuing to contract rhythmically, confidently goes into the depths.
Kornerot is sensitive to changing weather conditions. For example, before a storm, jellyfish move away from the shore and sink to the bottom.
Cornerot helps fish fry to survive in the sea, hiding under its umbrella from predators. Cornerot itself feeds exclusively on plankton, but no one eats cornerot in the sea. Scientists classify jellyfish as “food dead ends,” although jellyfish dishes have been cooked in Japan, Korea and China for more than 1,700 years. They are recommended for high blood pressure and other diseases; they are a dietary product.
Even in the Middle Ages, diuretics and laxatives were made from cornet. And now medicines are produced from jellyfish venom to treat pulmonary diseases and regulate blood pressure.
Jellyfish are present in Japanese sushi recipes. In Thailand they are used to make noodles. In China, they have been salted or dried for more than 1,000 years (the result is something like dried mushrooms or thin brown pancakes). In 2006, during the mass reproduction of large jellyfish off the coast of Japan, these jelly-like creatures were even used as a filling for pies, and soups were made from them.
The mesoglea of the cornerota umbrella contains 98.25% moisture and 1.75% dry matter, which includes 72.59% mineral and 27.41% organic substances, including 15.80% protein and 1.03% fat . Jellyfish protein is complete and contains 17 amino acids, including a full set of essential ones.
Scientific classification:
Kingdom: Animals
Type: Cnidarians - Cnidaria (Hatschek, 1888)
Class: Scyphozoa - Scyphozoa (Gotte, 1887)
Squad: Cornerota - Rhizostomeae (Cuvier, 1799)
Suborder: Daktyliophorae
Family: Rhizostomatidae (Cuvier, 1799)
Genus: Rhizostoma (Cuvier, 1800)
View: Cornermouth - Rhizostoma pulmo (Macri, 1778)
Rhizostoma pulmo
Kingdom: Animalia (animals)
Type: Coelenterata (coelenterata)
Class: Scyphozoa (scyphoid)
Order: Rhizostomea (root-mouthed jellyfish)
Family: Rhizostomatidae (rootmouths)
Genus: Rhizostoma
Specimen: Rhizostoma pulmo
In the shallow waters of Blagoveshchenka, I met the cornet jellyfish only once. A very beautiful jellyfish with a heavy, fleshy dome and lacy mouth lobes.
Everyone knows that the cornet jellyfish can sting with its stinging cells like nettles. Therefore, it is better not to touch it by its mouth lobes (tentacles), but to gently push it away by its dome if it ends up in the water near the swimmer.
Burn from the cornerota jellyfish can be quite unpleasant. It depends on how your body reacts to the substances contained in the stinging cells of the jellyfish. The biggest problem is that the burn can cause an allergic reaction. Throwing jellyfish is a favorite pastime for children, everyone knows this. Children suffer the most from jellyfish stings.
Corneroth jellyfish feeds on plankton. By moving the umbrella, the jellyfish creates a jet stream of water, from which it catches plankton, which it then swallows through its mouth openings.
On the oral lobes there are an abundance of stinging cells, with which the jellyfish paralyzes planktonic organisms.
The Russian name cornerot is a literal translation of the Latin name of the jellyfish Rhizostoma (from the Greek rhiza - root and stoma - mouth). This jellyfish is common in the Black and Azov Seas, and can even be found in desalinated Black Sea bays and estuaries. Outside of Russia, the cornet lives in the Mediterranean Sea and along the Atlantic coast of Europe from the Strait of Gibraltar to the Lofoten Islands off the northern coast of Norway.
Cornerotes are very beautiful and beautifully swimming jellyfish. Their strongly convex umbrella is white with a faint yellowish or greenish tint and looks great against the background of the blue sea water. And along the very edge of the umbrella, like a thin trim, there is a bright purple, blue or light blue stripe (see textbook illustration, p. 110).
A peculiarity of the corner jellyfish is their lack of tentacles along the edge of the umbrella. Catching prey is carried out exclusively with mouth blades.
The edges of the mouth of cornerotes are elongated into four lobes, which can be forked or even highly branched. The skin folds of these numerous lobes in many places grow together and form peculiar tubes. As a result, the mouth opening turns out to be completely overgrown and surrounded by many shoots hanging down and resembling plant roots. Indeed, a real cornerrot. The overgrowth of the mouth led to a change in the jellyfish’s lifestyle. Large food became unavailable to it, and the jellyfish switched to feeding on plankton. Small organisms suspended in seawater easily pass through the pores in the oral lobes and then through special channels enter the pharynx and digestive cavity.
The diameter of the cornerot bell can reach 60cm. The digestive cavity inside it is represented by 16 radial canals diverging from the stomach to the edges of the umbrella. Approximately halfway along the length, all channels are connected to each other by a ring channel. Thus, the entire digestive system is closed, there is only one opening - the mouth. Undigested food remains are also removed through this hole.
A peculiarity of the life cycle of Cornerota is the absence of a polyp stage. At least the polypoid stage of this species has not yet been described by scientists.
Some types of rootmouths can have more than one and a half hundred “roots”. Such, for example, are the edible Rhopilema jellyfish that live off the coast of Japan and China with an umbrella diameter of up to 20 cm. Specially salted, these jellyfish are known in East Asia as “crystal meat.” They are served as a seasoning for other dishes.
Another close relative of the Cornerot, the Cassiopeia jellyfish, not only has a beautiful mythological name, but is also distinguished by unusual behavior. After a short swim, it suddenly turns over with the top side of the umbrella down and attaches itself to some underwater object.
Cornerot is considered dangerous to humans as it can cause skin burns. And this jellyfish is quite large: some individuals have umbrellas the size of a football.
polar jellyfish
The polar jellyfish is one of the largest jellyfish in the fauna of Russia. In some specimens, the diameter of the bell reaches 2–2.5 m, and the tentacles, when extended, extend for 20–30 m. If you imagine that such a specimen is placed on the roof of a nine-story building, then its tentacles will touch the ground at the foot of the building.
The Latin name of the polar jellyfish is very beautiful - Suapea capillata. The famous Roman poet Ovid named one of the nymphs, who became the beloved of Miletus, after Cyaneus. Two thousand years later, in 1758, the Swedish scientist Carl Linnaeus remembered the poems of Ovid, looking for a name for the largest jellyfish. Probably the long tentacles of the polar jellyfish reminded Linnaeus of the luxurious long hair of Ovid’s Cyanea. After all, the second word in the name of the species - “capillata” - just means “long-haired”!
The polar jellyfish got its name for a reason. It really prefers cold waters and is common in our northern seas - from the Barents to the Chukchi Sea. It can also be found in the northern seas of the Pacific Ocean and even in the western, least desalinated part of the Baltic Sea. The variability of the species is very great, and in different seas there are special geographical races of the polar jellyfish.
The most common are individuals with a whitish or yellowish bell, the edges of which are painted dark red. With age, the color of jellyfish brightens, but young polar jellyfish are very bright. The wide mouth lobes of the jellyfish are a rich red color, and the tentacles are much lighter - pale pink.
In the Sea of Okhotsk there is a special species - Purple Cyanea. Its bell reaches a diameter of 35 cm and, in accordance with the name of the species, has a purple color.
Small species of cyanea live off the east and west coasts of the United States. The venom of one jellyfish can cause loss of consciousness and even death in a person.
Cyane jellyfish prefer surface layers of water and do not move away from the coasts.
The main food of jellyfish consists of various types of fish. Thus, cyanides living in the White Sea actively eat stickleback, especially during its spawning.
On the other hand, the tentacles of jellyfish hanging down like giant beards are used by many marine fish as a place where they can perfectly hide from danger.
Sometimes schools of fry of some fish stay right under the bell of the jellyfish. This is what, for example, the fry of the Far Eastern navaga do.
Polar jellyfish that reach a diameter of 4 cm are already sexually mature.
Medusa octomanus
Medusa octomanus belongs to a small but very interesting group of scyphoid jellyfish that do not swim in the water column, but live on the bottom and lead an attached lifestyle. Their short, closely spaced tentacles look a bit like a hedge. Probably for this reason, sessile jellyfish were called stavromedusae (translated from Greek “stavros” means “picket fence”) (see textbook illustration, p. 112).
Staurojellyfish do not swim at any stage of their life cycle, which is not typical for coelenterates. After all, even heavy and motionless corals, at a certain period of life, have tiny floating larvae with cilia. And in stavromedusas, the larvae are “naked”, and the only way for them to move can be crawling along the bottom.
Having found a place suitable for life, such “worm” larvae accumulate several individuals and in such a small group begin an independent life. They feed on small animals passing by, which the jellyfish larvae catch with the help of stinging cells.
After some time, the gradual transformation of larvae into adult jellyfish begins. The larvae turn into small polyps, which begin to grow tentacles. Eventually a creature appears that resembles an elegant bowl or vase on a short stem. The edges of this “vase” are extended into eight short processes, each of which ends in a bunch of numerous short tentacles. These processes are mobile, and, apparently, due to the similarity of the tentacles to fingers, zoologists call them “hands”.
Staurojellyfish live both in shallow sea waters and on the bottom of the oceans. Sometimes they are found at a depth of about 3000m. Where algae grow, jellyfish attach themselves to it with their legs and even take on the color of the type of algae they live on.
Science knows about 40 species of staurojellyfish. In the seas washing Russia, the most common staurojellyfish are from the genera Haliclystus and Lucernaria. The former prefer the seas of the Pacific Ocean, and alfalfas are found in the Atlantic and Arctic seas - the Black, Barents, Kara, etc. All these jellyfish are relatively small. The diameter of their cups usually ranges from 7 to 20 mm, and the length of the stem rarely exceeds 3 cm. Only some alfalfa reach a height of 10–15 cm.
In 1961 A remarkable event occurred in the history of the study of jellyfish. The famous expert on coelenterates Donat Vladimirovich Naumov discovered a new and very unusual species of stavromedus. Specimens of this species were found near one of the southernmost islands of the Kuril ridge - Shikotan Island. The structure of this jellyfish was so strange that they created a separate genus for it and gave it the name Octomanus, which literally means “eight-armed.”
Octomanus belongs to the staurojellyfish, which are characterized by additional capitate tentacles along the edge of the umbrella. Experts call them “ropalioids.” The tops of these tentacles are modified and resemble a suction cup or a grasping paw. A peculiarity of Octomanus is that its rapalioids sit on the edges of the calyx, and their suckers are relatively large and allow them to grasp small objects. In combination with well-developed muscle cords, rapalioids become suction organs and help the movement of the jellyfish.
The only species of Octomanus known to scientists is called Octomanus monstrosus, i.e. eight-armed is extraordinary. Its calyx has a diameter of 10 mm, and the stem is even smaller - only 3–4 mm. Each of the eight "arms" of Octomanus ends in about a hundred suckers. The jellyfish was found at depths not exceeding 24m. Perhaps Octomanus also lives off the coast of the Japanese islands.
Octomanus and other staurojellyfish pose a mystery to scientists. In some ways they are similar to jellyfish, while in others they resemble polyps. According to D.V. Naumov, they represent a stage of evolution at which the jellyfish formed on the polyp does not separate and does not become independent, but remains to live on the mother’s body. This is how motionless creatures with the sole of a polyp and the “head” of a jellyfish appear.