Zoology of invertebrates. External and internal structure of cephalopods on the example of sepia Structure and vital functions
Species: Sepia apama = Giant Australian cuttlefish
The giant Australian cuttlefish can reach 50 centimeters in length and is considered the largest cuttlefish in the world. Its weight can reach from 3 to 10 kilograms. There is sexual dimorphism in size - males always outnumber females in size.
The Giant Australian Cuttlefish is an endemic Australian species. It lives exclusively in coastal waters in the south, southwest and southeast coasts of Australia, from the coast of Queensland to Shark Bay in Western Australia. And there is a giant Australian cuttlefish at depths of up to about 100 meters, but even more often prefers shallow water.
The giant Australian cuttlefish has a body slightly flattened in the dorsal-abdominal direction, which is decorated with a wide leathery fold on the sides. Here, on the sides of the body, there are also fins - the main organ of their movement in the water. The head end of the urvkatica is adorned with 10 tentacles. Of these, 2 tentacles are grasping, they are the longest, although they can be completely retracted into special sac-like pits under the eyes. The remaining 8 tentacles are short, and all are located around the mouth, framing it. All tentacles are equipped with suction cups that are very necessary for the animal. There is a difference in the structure of the tentacles of cuttlefish of both sexes. So in a male, unlike females, the 4th tentacle serves to fertilize females.
The respiratory organ of cuttlefish is the gills. On the dorsal side of the body under the mantle, there is a porous calcareous shell, which looks like a plate, which gives the animal a fixed body shape. The eyes are similar in structure and visual acuity to human eyes. Cuttlefish, if necessary, are able to change the shape of the lens. Their mouth, like that of other cephalopods, consists of a strong beak, which is shaped like the beak of birds, especially a parrot, there are also jaws and a tongue.
Speaking about the features of the internal structure of cuttlefish, it remains unclear why nature endowed these creatures with 3 hearts. In this case, one is responsible for the blood supply to the nervous system, and the other two are responsible for the coordinated work of the gills. And the blood of cuttlefish is not red, but blue. The blue color of blood is caused by the presence of a special pigment called hemocyanin in it. Hemocyanin, like hemoglobin in vertebrates, is responsible for the transport of oxygen.
The giant Australian cuttlefish is known for its unique ability to instantly change its color, which can depend both on the mood of the animal and the characteristics of the environment. The coloration of males changes greatly during the mating season. This becomes possible due to the presence of a special pigment in the cells of the body, which is responsible for their stretching or contraction, depending on the signals from the nervous system. During the mating season or during an attack on prey, their color acquires a metallic sheen and is covered with bright luminous dots.
An interesting feature of this species is that during the mating season, males can sometimes pretend to be females in order to try to outwit a stronger rival and try to get closer to the female. If they succeed in this maneuver, they mate with her very quickly and retreat until the dominant male has figured out what's what ...
Giant squids use their ink stores as a defense against predators. In case of danger, the squid releases an ink cloud either directly into the “face” of the enemy, after which, under its cover, they quickly hide away, or a little to the side. At the same time, the spot often takes on such a shape that it becomes a bit similar in shape to the cuttlefish itself, and this, albeit for a short time, distracts the attention of the predator from the cuttlefish's own person.
The giant Australian cuttlefish is predominantly nocturnal. They spend most of their time hiding among kelp beds, rocky reefs, or simply burrowing into the seabed. Cuttlefish are homebodies, they spend almost all their active time on a small territory, not exceeding 500 m2. Therefore, they spend most of the food energy absorbed by them not on physical activity, but on their own growth.
The giant cuttlefish is very curious and is not averse to even playing, which is often used by divers. Despite their relatively peaceful nature and cute appearance, cuttlefish are dexterous predators, extracting various small mollusks and crustaceans, fish, sea worms and even small cuttlefish for food. Cuttlefish go hunting at night, attacking prey from an ambush, grabbing it with two long tentacle arms.
By their nature, cuttlefish are solitary, and only during the breeding season, which falls on June-August, they often gather in large groups. One such favorite place for marriage dates is False Bay, located in the northern part of Spencer Bay. At this time, it is simply teeming with giant cuttlefish, and at this time there are almost 1 individual per 1 m2. This is where the fun begins. The largest and strongest males begin to care for the females. They "put on" a bright wedding dress and begin to wave their long "arms" in front of their chosen one. At the same time, they drive away smaller and younger males. Then they are forced to go for a deceptive maneuver, changing their bright cavalier outfit to "ladies'" and under the guise of "females" they try to make their way through the "vigilant guard" to the females. And if the dominant male is distracted for a few moments, the werewolf immediately quickly acquires his bright male color in front of the female and mates with her, transferring his spermatophores to her with the help of the 4th “hand”, and quickly swims away from trouble.
After some time, females lay eggs under stones or in other hard-to-reach places, enclosed in a thick shell. After that, they die. And the cubs are born, depending on the temperature of the water, after 3-5 months, having a body length of about 2.5 centimeters. Outwardly, they are very similar to adults, and at this age they feed only on plankton.
The meat of the giant cuttlefish is edible and is widely used in cooking as food. Cuttlefish ink is still used in painting today. Therefore, large-scale capture of this species for export is currently underway, because of which the giant cuttlefish is already under the threat of decline in numbers. Now the capture of the giant Australian cuttlefish in False Bay in Australia is prohibited.
Latin name Cephalopoda
Cephalopods General characteristics
The most highly organized animals among invertebrates. This is a relatively small group (about 730 species) of marine predators whose evolution is associated with shell reduction. Only the most primitive four-gill mollusks have an external shell. The rest of the two-gill cephalopods, capable of fast and long movements, have only rudiments of the shell, which play the role of internal skeletal formations.
Cephalopods are usually large animals, their body length is at least 1 cm. Among deep-sea forms, there are giants up to 18 m. Pelagic cephalopods (squids) have a streamlined body shape (similar to a rocket), they move the fastest. At the rear end of their body there are fins - movement stabilizers. Benthic forms - octopuses - have a sac-like body, the front end of which forms a kind of parachute due to the fused bases of the tentacles.
External structure
The body of cephalopods consists of a head and a body. The leg, which is characteristic of all mollusks, is greatly modified in them. The back of the leg has turned into a funnel - a conical tube leading to the mantle cavity. The funnel is located behind the head on the ventral side of the body. It is the organ by which molluscs swim. In a cephalopod of the genus Nautilus, which has retained many of the most ancient features of the structure of cephalopods, the funnel is formed by folding into a tube a leaf-shaped leg, which has the usual wide sole. At the same time, the wrapping edges of the leg do not grow together. Nautiluses either slowly crawl along the bottom with their feet, or rise and swim slowly, carried by the currents. In other cephalopods, the funnel lobes are primarily separate, while in adult animals they fuse into a single tube.
Around the mouth are tentacles, or arms, which are seated with several rows of strong suckers and have powerful muscles. It turns out that the tentacles of cephalopods, like the funnel, are homologues of part of the leg. In embryonic development, the tentacles are laid on the ventral side behind the mouth from the leg bud, but then move forward and surround the mouth opening. The tentacles and infundibulum are innervated by the pedal ganglion. The tentacles of most cephalopods are 8 (in octopuses) or 10 (in decapods), in primitive molluscs of the genus Nautilus - up to 90. The tentacles serve to capture food and move; the latter is characteristic mainly of benthic octopuses, which walk along the bottom on their tentacles. The suckers on the tentacles of many species are armed with chitinous hooks. In decapods (cuttlefish, squids), two out of ten tentacles are much longer than others and are seated at the widened ends with suckers. These are tentacles.
Mantle and mantle cavity
The mantle covers the entire body of cephalopods; on the dorsal side it fuses with the body, on the ventral side it covers an extensive mantle cavity. The mantle cavity communicates with the external environment through a wide transverse slit located between the mantle and the body and running along the front edge of the mantle behind the funnel. The wall of the mantle is very muscular.
The structure of the muscular mantle and funnel is a device with which cephalopods swim, and move forward with the posterior end of the body. This is a kind of "rocket" engine. In two places on the inner wall of the mantle at the base of the funnel there are cartilaginous protrusions called cufflinks. When the musculature of the mantle contracts and presses against the body, the front edge of the mantle, with the help of cufflinks, is, as it were, "fastened" to the recesses at the base of the funnel, and the gap leading to the mantle cavity closes. In this case, water is forced out of the mantle cavity through the funnel. The body of the animal is thrown back by a push some distance back. This is followed by relaxation of the muscles of the mantle, the cufflinks are “unfastened” and water is sucked through the mantle gap into the mantle cavity. The mantle contracts again and the body receives a new push. Thus, the contraction and stretching of the mantle muscles that quickly follow each other alternately make it possible for cephalopods to swim at high speed (squids). The same mechanism creates the circulation of water in the mantle cavity, which ensures respiration (gas exchange).
The gills are located in the mantle cavity, having the structure of typical ctenidia. Most cephalopods have one pair of ctenidia, and only the nautilus has 2 pairs. This is the basis for the division of the class of cephalopods into two subclasses: two-gill (Dibranchia) and four-gill (Tetrabranchia). In addition, the anus, a pair of excretory openings, genital openings and openings of the nidamental glands open into the mantle cavity; in the nautilus, osphradia are also placed in the mantle cavity.
Sink
Most modern cephalopods do not have a shell at all (octopuses) or it is rudimentary. Only the nautilus has a well-developed thin shell. It should be borne in mind that the nautilos genus is very ancient, having changed very little since the Paleozoic. The shell of a nautilus is twisted spirally (in the plane of symmetry) onto its head. Inside, it is divided into chambers by partitions, and the body of the animal is placed only in the front part, the largest chamber. From the back of the body of the nautilus, a process of a siphon departs, which passes through all the partitions to the top of the shell. With the help of this siphon, the chambers of the shells are filled with gas, which reduces the density of the animal.
Modern bibranch cephalopods are characterized by an underdeveloped internal shell. The most complete spiral shell is preserved only in the small mollusk spirula, which leads a benthic lifestyle. In the cuttlefish, the shell leaves a wide and thick porous calcareous plate lying on the dorsal side under the mantle. It has a supporting function. In squids, the shell is represented by a narrow dorsal chitinoid plate. Some octopuses have two conchiolin sticks under the mantle. Many cephalopods have completely lost their shells. Shell rudiments play the role of skeletal formations.
In cephalopods, for the first time, an internal cartilaginous skeleton appears, which has protective and supporting functions. The bibranchs have a cartilaginous head capsule surrounding the central nervous system and statocysts, as well as cartilage of the bases of the tentacles, fins, and cufflinks of the mantle. The four-gills have a single cartilage that supports the nerve centers and the anterior end of the digestive system.
Digestive system
The mouth is at the front end of the body and is always surrounded by a ring of tentacles. The mouth leads into a muscular pharynx. It is armed with powerful horny jaws, similar to the beak of a parrot. The radula is located at the back of the pharynx. The ducts of one or two pairs of salivary glands open into the pharynx, the secret of which contains digestive enzymes.
The pharynx passes into a narrow long esophagus, which opens into a sac-like stomach. In some species (for example, in octopuses), the esophagus forms a lateral protrusion - goiter. The stomach has a large blind appendage into which the ducts of the usually bilobed liver open. The small (endodermic) intestine departs from the stomach, which makes a loop, heading forward, and passes into the rectum. The rectum, or hindgut, opens with an anus, or powder, in the mantle cavity.
The duct of the ink sac flows into the rectum before the powder. This pear-shaped gland secretes an inky liquid, which is ejected through the anus and creates a dark cloud in the water. The ink gland serves as a protective device that helps its owner to hide from persecution.
Respiratory system
The gills, or ctenidia, of cephalopods are arranged symmetrically in the mantle cavity in one or two pairs. They have a feathery structure. The epithelium of the gills is devoid of cilia, and the circulation of water is provided by rhythmic contractions of the muscles of the mantle.
Circulatory system
The heart of cephalopods usually consists of a ventricle and two atria, only the nautilus has four. Two aortas depart from the ventricle - the head and abdominal, branching into a number of arteries. Cephalopods are characterized by a large development of arterial and venous vessels and capillaries, which pass into each other in the skin and muscles. The circulatory system becomes almost closed, the lacunae and sinuses are less extensive than in other molluscs. Blood from the organs is collected through the venous sinuses into the vena cava, which form blind protrusions protruding into the walls of the kidneys. Before entering the ctenidium, the afferent gill vessels (vena cava) form muscular extensions, or venous hearts, which pulsate and promote blood flow to the gills. Enrichment of blood with oxygen occurs in the capillaries of the gills, from where arterial blood enters the atria.
The blood of cephalopods is blue because its respiratory pigment, hemocyanin, contains copper.
Secondary body cavity and excretory system
In cephalopods, as in other molluscs, there is a reduction in the secondary body cavity, or coelom. The most extensive coelom, containing the heart, stomach, part of the intestine and gonads, is found in primitive four-branched cephalopods. In decapods, the coelom is more strongly reduced and is represented by two separate areas - pericardial and genital; in the eight-legged bibranchs, the pericardial coelom contracts even more and contains only the pericardial glands, while the heart lies outside the coelom.
The excretory organs are represented by two or four kidneys. They usually begin as funnels in the pericardial cavity (in some forms, the kidneys lose contact with the pericardium) and open with excretory openings in the mantle cavity, on the sides of the powder. The kidneys are closely associated with blind protrusions of the venous vessels, through which filtration and removal of metabolic products from the blood takes place. The pericardial glands also have an excretory function.
Nervous system
Bibranch cephalopods surpass the height of the organization of the nervous system of all invertebrates. All the ganglia characteristic of these mollusks converge and form the brain - a common nerve mass surrounding the beginning of the esophagus. Separate ganglia can only be distinguished on cuts. There is a division of paired pedal ganglia into tentacle ganglia and infundibulum ganglia. From the back of the brain, nerves depart, innervating the mantle and forming two large stellate ganglia in its upper part. The buccal ganglia give off sympathetic nerves that innervate the digestive system.
The primitive four-gill nervous system is simpler. It is represented by three nerve semirings, or arcs - supraesophageal and two subesophageal. Nerve cells are distributed on them evenly, without forming ganglionic clusters. The structure of the nervous system of four-gills is very similar to that of chitons.
sense organs
In cephalopods, they are highly developed. Tactile cells are located throughout the body, they are especially concentrated on the tentacles.
The olfactory organs of the two-gills are special olfactory pits, and only the nautilus, that is, the four-gills, have osphradia.
All cephalopods have complex statocysts located in a cartilaginous capsule surrounding the brain.
The most important role in the life of cephalopods, especially in hunting for prey, is played by eyes, very large and of great complexity. The most simple are the eyes of the nautilus. They represent a deep eye fossa, the bottom of which forms the retina.
The eyes of bibranch cephalopods are much more complex. The eyes of a cuttlefish have a cornea, an iris, a lens, a vitreous body, and a highly developed retina. The following structural features of the cephalopod eye are noteworthy. 1. Many molluscs have a small hole in the cornea. 2. The iris also forms a hole - the pupil leading to the anterior chamber of the eye. The pupil can contract and expand. 3. A spherical lens formed by two fused halves is not able to change curvature. Accommodation is achieved with the help of special eye muscles that remove or bring the lens closer to the retina, as is done when focusing the lens of a photographic camera. 4. The retina consists of a huge number of visual elements (per 1 mm 2 of the retina there are 105,000 in cuttlefish, and 162,000 visual cells in squid).
The relative and absolute size of the eyes in cephalopods is larger than in other animals. So, the eyes of a cuttlefish are only 10 times less than the length of its body. The diameter of the eye of a giant octopus reaches 40 cm, and that of a deep-sea squid is about 30 cm.
Reproductive system and reproduction
All cephalopods are dioecious, and some have very pronounced sexual dimorphism. An extreme example in this regard is the wonderful octopus mollusk, the boat (Argonauta argo).
The female boat is relatively large (up to 20 cm) and has a shell of a special origin, not homologous to the shell of other mollusks. This shell is distinguished not by the mantle, but by the leg lobes. The shell is thin, almost transparent and spirally twisted. It serves as a brood chamber in which eggs are hatched. The male boat is many times smaller than the female and does not have a shell.
The gonads and genital ducts in most cephalopods are unpaired. Females are characterized by the presence of two or three paired and one unpaired nidamental glands that secrete a substance from which the egg shell is formed. In males, spermatozoa are enclosed in spermatophores of various shapes.
Of great interest is the method of fertilization in cephalopods. They do not actually mate. In sexually mature males, one of the tentacles is strongly modified, it turns into a hectocotylized tentacle, or hectocotyl. With the help of such a tentacle, the male takes spermatophores from his mantle cavity and transfers them to the mantle cavity of the female. In some cephalopods, especially in the boat (Argonauta) described above, the hectocotylized tentacle has a complex structure. After filling the tentacle with spermatophores, it breaks off and swims on its own, and then climbs into the mantle cavity of the female, where fertilization occurs. Instead of the detached hectocotyl, a new one regenerates.
Large cephalopod eggs are laid in groups on various underwater objects (under stones, etc.). Eggs are covered with a dense shell and are very rich in yolk. Cleavage is incomplete, discoidal. Development is direct, without metamorphosis. A small mollusc comes out of the egg, similar to an adult.
Classification
The class of cephalopods (Cephalopoda) is divided into two subclasses: 1. Tetrabranchia; 2. Double gill (Dibranchia).
Subclass Tetrabranchia
This subclass is characterized by the presence of four gills and a large outer shell, divided by partitions into many chambers. The subclass is divided into two orders: 1. Nautilids (Nautiloidea); 2. Ammonites (Ammonoidea).
Nautilids in modern fauna are represented by only one genus - Nautilus, which includes several species. They have a very limited distribution in the Southwest Pacific. Nautilids are characterized by many features of a more primitive structure: the presence of a shell, an unfused funnel leg, the remains of metamerism in the form of two pairs of gills, kidneys, atria, etc. Nautilids have survived little changed to our time since the Paleozoic. These living fossils are the remains of a once rich fauna of four-gilled cephalopods. Up to 2500 fossil species of nautilids are known.
Ammonites are a completely extinct group of four-gill mollusks that also had a spirally twisted shell. Over 5,000 fossil ammonite species are known. The remains of their shells are common in Mesozoic deposits.
Subclass Dibranchia
The subclass of bibranchs is characterized by an internal reduced shell (or its absence); their respiratory organs are represented by two gills. The subclass is divided into two orders: 1. Decapods (Decapoda); 2. Octopus (Octopoda).
Order Decapods (Decapoda)
For decapods, the presence of 10 tentacles is most characteristic, of which 2 are trapping, many retain a rudiment of a shell. Representatives are cuttlefish (Sepia officinalis), various types of fast-swimming squids from the genus Ommatostrephes (hundreds of herring chasing shoals), from the genus Loligo, etc.
Decapods already existed in the Triassic, and they had an inner, but more developed shell. Often found in Mesozoic deposits with devil's fingers "are the remains of the back of the shell of the Mesozoic decapod belemnites (Belemnoidea) - pelagic animals resembling squid in shape.
Order Octopus (Octopoda)
Unlike decapods, these are predominantly benthic animals, with eight tentacles, devoid of a shell. Representatives are different types of octopuses, as well as Argonauta and others.
The most important representatives of the class of cephalopods and their practical significance
Modern cephalopods are an essential part of marine and oceanic fauna. They are distributed mainly in the southern seas and in seas with a fairly high salinity. In Russia, most of the cephalopods are in the Far Eastern seas. There are also cephalopods in the Barents Sea. Cephalopods do not live in the Black and Baltic Seas due to the low salinity of these seas. There are cephalopods at very different depths. Among them are many deep-sea forms. Being predators, cephalopods feed on various marine animals: fish, crustaceans, mollusks, etc. Some of them cause great harm, destroying and spoiling shoals of valuable commercial fish. Such, for example, are the Far Eastern squid Ommatostrephes sloani pacificus.
Among cephalopods there are very large forms, up to 3-4 m and more. The largest known cephalopod is the deep-sea squid (Architeuthis dux), a decapod squid. This real giant among cephalopods, and indeed among invertebrates, reaches a length of 18 m, with a length of tentacles of 10 m and a diameter of each tentacle of 20 cm. We know about such giants, which, unfortunately, have not yet been caught in a living form, we know from their remains. found in the stomachs of dead toothed whales - sperm whales. Many toothed whales feed on cephalopods, as well as other predators of the seas: sharks, pinnipeds (seals), etc.
Cephalopods are also eaten by humans. So, cuttlefish and octopuses are eaten by the population of the Mediterranean countries. In many countries, cuttlefish and squid are the subject of fishing.
There are about 650 species of cephalopods, the most highly organized molluscs, ranging in size from 1 cm to 5 m (and even up to 13 m - this is the body length of a giant squid). They live in the seas and oceans, both in the water column and at the bottom. This group of mollusks includes octopuses, squids and cuttlefish (Fig. 81).
Rice. 81. Variety of cephalopods: 1 - octopus; 2 - nautilus; 3 - squid; 4 - cuttlefish; 5 - argonaut
These mollusks are called cephalopods because their leg has turned into tentacles, which are located on the head with a corolla, around the mouth opening.
External building. The body of cephalopods is bilaterally symmetrical. It is usually divided by an interception into a body and a large head, and the leg is modified into a funnel located on the ventral side - a muscular conical tube (siphon) and long muscular tentacles located around the mouth (Fig. 82). Octopuses have eight tentacles, cuttlefish and squid have ten. The inner side of the tentacles is covered with numerous large disc-shaped suckers.
Rice. 82. Appearance and internal structure of an octopus: 1 - horny jaws; 2 - brain; 3 - siphon; 4 - liver; 5 - pancreas; 6 - stomach; 7 - mantle; 8 - gonad; 9 - kidney; 10 - heart; 11 - gills: 12-ink bag
The body is covered with a mantle on all sides. At the point of transition of the body to the head, the mantle cavity communicates with the external environment through a slit-like opening. Sea water is sucked into the mantle cavity through this gap. Then the gap is closed with special cartilaginous "cufflinks". After that, the water from the mantle cavity is forced out through the funnel, giving the animal a back push. In this way, cephalopods move the rear end of the body forward in a jet way. The speed of movement of some squids can exceed 50 km/h. Cuttlefish and squid have additional swimming organs - a pair of fins on the sides of the body.
Cephalopods are able to quickly change the color of the body; deep-sea species have organs of luminescence.
Internal skeleton. In most cephalopods, the shell is almost not developed (reduced) and is hidden in the body of the animal. In a cuttlefish, the shell looks like a calcareous plate lying under the integument on the dorsal side of the body. The squid has a small “feather” left from the shell, while the octopus has no shell at all. The disappearance of the shell is associated with the high speed of movement of these animals.
Cephalopods have a special internal skeleton formed by cartilage: the brain is protected by a cartilaginous skull, supporting cartilages are at the base of the tentacles and fins.
Digestive system. The mouth opening (in the crown of the tentacles) is surrounded by two thick horny black or brown jaws, curved like a parrot's beak. The tongue is located in a highly developed muscular pharynx. There is a grater on it, with the help of which animals grind food. The ducts of poisonous salivary glands flow into the pharynx. Next come a long esophagus, a muscular sac-like stomach, and a long intestine that ends in an anus. A duct of a special gland, the ink sac, opens into the hindgut. In case of danger, the mollusk releases the contents of the ink bag into the water and, under the protection of this “smoke screen”, hides from the enemy.
All cephalopods are predators, attacking mainly fish and crustaceans, which they grab with their tentacles and kill with a bite from their jaws and poison from the salivary glands. Some animals of this class eat mollusks, including cephalopods, carrion, and plankton.
Nervous system. In cephalopods, it reaches a high complexity. The nerve nodes of the central nervous system are very large and form a common peripharyngeal nerve mass - the brain. Two large nerves depart from its posterior section.
sense organs well developed. According to the complexity of the structure and visual acuity, the eyes of cephalopods are not inferior to the eyes of many vertebrates (Fig. 83). Among the cephalopods, especially large-eyed ones are found. The diameter of the eye of a giant squid reaches 40 cm. Cephalopods have organs of chemical sense, balance, tactile, light-sensitive and taste cells are scattered in the skin.
Rice. 83. Scheme of the structure of the eye of a cephalopod mollusk: 1 - refractive lens; 2 - layer of light-perceiving sensitive cells
Respiratory system. Most cephalopods have one pair of gills, which are located in the mantle cavity. Rhythmic contractions of the mantle serve to change the water in the mantle cavity, providing gas exchange.
Circulatory system. In cephalopods, it is almost closed - in many places, the arteries, after oxygen is released to the tissues, pass through the capillaries into veins. The heart consists of one ventricle and two atria. Large vessels depart from the heart, which are divided into arteries, and those, in turn, into a network of capillaries. The afferent vessels carry venous blood to the gills. Before entering the gills, the afferent vessels form muscular extensions, the so-called venous hearts, which, with their rhythmic contractions, contribute to the rapid flow of blood into the gills.
The number of heartbeats in cephalopods is 30-36 times per minute. Instead of hemoglobin, which contains iron, which causes the red color of blood in vertebrates and humans, the blood of cephalopods contains a substance that includes copper. Therefore, the blood of cephalopods is bluish in color.
Reproduction. Cephalopods are dioecious, and sexual dimorphism (differences in the size and external structure of the male and female) is pronounced in some species, for example, in the argonaut (Fig. 84).
Rice. 84. Argonaut: A - female; B - male
Fertilization occurs in the mantle cavity of the female. The role of the copulatory organ is played by one of the tentacles. The spermatozoa of males stick together in packets surrounded by a dense membrane - spermatophores.
The eggs of cephalopods are large, rich in yolk. There is no larval stage. A young mollusk comes out of the egg, similar in appearance to an adult animal. Female squids and cuttlefish attach eggs to underwater objects, and octopuses guard their clutches and juveniles. Usually cephalopods reproduce once in their life, after which they die.
Man uses cephalopods: squid, octopus, cuttlefish eats; from the secretion of the cuttlefish's ink sac it receives sepia watercolor paint.
Cephalopods are a small group of highly organized animals, distinguished by the most perfect structure and complex behavior among other mollusks.
Lesson learned exercises
- According to Figure 81, describe the features of the external structure and movement of cephalopods.
- What are the distinguishing features of the following cephalopod organ systems: digestion, respiration, nervous, circulatory systems.
- The structure of what organs confirms the higher level of organization of mollusks? Explain with examples.
- What is the importance of representatives of cephalopods in nature and human life?
General characteristics of cephalopods
This class includes about 700 species of large mollusks that live exclusively in the seas and are distinguished by the most complex organization. Because of the perfect adaptations to life in the sea and the complexity of the behavior of cephalopods, they are often called the "primates of the sea" among invertebrates. Usually these are free-swimming and mobile predators, preferring the waters of warm seas and oceans. Among them there are few watering species. Their sizes range from a few centimeters to 18 m (giant squids).
The body is distinctly divided into head and trunk. The leg is turned into tentacles (arms), which again shifted to the head and surround the mouth opening (bag-shaped (octopuses), in other universal species the body is flattened (cuttlefish). In planktonic forms, the body is gelatinous, medusoid-shaped, can be narrow or even spherical. In higher cephalopods, the mouth opening is surrounded by eight or ten tentacles. Octopoda gradually narrow towards the end on the side facing the mouth, they have numerous disc-shaped suckers, with which the molluscs can firmly stick to the substrate and to the victim. In the types of detachment Decapoda in addition to these eight tentacles, there are two more, but much longer trapping tentacles, widened at the end. On the sides of the head are two large and complex eyes. In primitive forms, the number of smooth and worm-like tentacles can reach several dozen.
The body is covered on all sides with a mantle: on the back it forms the integuments of the body, and on the ventral side - a mantle cavity that communicates with the external environment through a slit-like opening. This hole can be closed and isolate the mantle cavity from the external environment. It closes with the help of special "fasteners-buttons". Between the "buttons" on the ventral side, a funnel protrudes from this gap in the form of a muscular tube. The expanded end of the funnel opens into the mantle cavity, and the narrow end opens outward. The funnel (a derivative of the leg) serves for a special jet propulsion. When the mantle gap is closed by contactors with the help of numerous muscles, the mantle is pressed against the body. Water from the mantle cavity is pushed out with force through the funnel, pushing the mollusk in the opposite direction (jet thrust). The funnel can be bent in different directions, which allows the mollusk to change the direction of movement. The role of an additional steering wheel is performed by tentacles and fins in the form of a fold of skin. Rhythmic contractions of the mantle and expulsion of water allow the mollusk not only to swim, but also to intensively wash the gills with water.
The genital and urinary ducts, as well as the anus, open into the mantle cavity on the ventral side of cephalopods, hence their name - cephalopods). The other part of the leg was transformed into a funnel lying at the entrance to the mantle cavity on the ventral side of the body.
In primitive forms, the shell is external; in higher representatives, it is internal; it can be partially or completely reduced.
Structure and life functions
Mollusks that live in the water column have a torpedo-shaped body (squid), while benthic forms have a body.
In modern cephalopods, the shell is greatly reduced and is overgrown with lateral folds of the mantle, becoming internal. Some representatives (cuttlefish sepia) the shell in the form of a calcareous plate lies under the covers on the dorsal side of the body. At the squid (Loligo) from the shell there remains only a dorsal horn sheet hidden under the integument. In some species, the shell remains only in females or disappears altogether.
covers represented by a single layer of epithelium and a layer of connective tissue underneath. Cephalopods are capable of a quick and abrupt change in their color, which is due to the presence of numerous pigment cells - chromatophores - in the connective tissue layer of the skin. The mechanism of color change is controlled by the nervous system, which receives information through the optic nerves.
Nervous system cephalopods have the most complex structure. The nerve ganglia form a large pharyngeal cluster - the brain, enclosed in a cartilaginous capsule (corresponds to the function of the skull of vertebrates). Two large mantle nerves depart from the posterior part of the ganglionic mass.
sense organs well developed: highly sensitive olfactory pits under the eyes, a pair of statocysts inside the cartilaginous head capsule, large and complex eyes capable of accommodation. The eyes are structurally similar to those of mammals (an example of convergence between invertebrates and vertebrates). The eyeball is covered from above by the cornea, which has an opening into the anterior chamber of the eye. The iris forms a hole - the pupil, through which light enters the lens. Accommodation of the eye occurs due to the removal of the lens from the retina or its approach (in mammals, accommodation is carried out by changing the curvature of the lens). The eyes are surrounded by a cartilaginous capsule. On the skin there are special organs of luminescence, in structure resembling eyes.
Digestive organs are also complex and have features of specialization in feeding on animal food. The mouth opening, which lies in the center of the crown of tentacles, leads to a muscular pharynx, in which there is a tongue with a grater. In the pharynx are two thick horny jaws, bent in the form of a hook and resembling a parrot's beak. The ducts of one or two pairs of salivary glands open into the pharynx, the secret of which has amylolytic and proteolytic activity, and may contain poisons. Cephalopods only feed on semi-liquid foods because they have a narrow esophagus that runs through the brain of the mollusk. The food is first gnawed by horny jaws, and then it is abundantly moistened with saliva and rubbed with a grater. Long esophagus. From the esophagus, food enters the muscular endodermal stomach, which has a blind saccular process. The small intestine departs from the stomach, passing into the hindgut, ending in the anus into the mantle cavity. The ducts of the liver flow into the stomach, the secret of which has the entire set of digestive enzymes. There is also a pancreas in the form of small appendages in the ducts of the liver. In front of the anus, the duct of the ink sac opens, in which a black liquid forms. Throwing this inky liquid through the anus, and then out of the mantle cavity through the funnel to the outside, the molluscs surround themselves with a dark cloud, which allows them to hide from enemies. Cephalopods feed mainly on fish, crabs and bivalves, grabbing them with tentacles and killing them with jaws and poison.
Respiratory system - gills located in the mantle cavity symmetrically on the sides of the body. The exchange of water is carried out by contraction of the mantle muscles and the work of a funnel through which water is pushed out. According to the number of gills, cephalopods are divided into two groups: four-gill (Tetrabranchia) and bibranchs (Dibranchia).
Circulatory system represented by a heart with one ventricle and two or four atria (according to the number of gills). Blood moves due to the contractions of the heart, as well as due to the pulsation of sections of the vessels. The head and splanchnic aorta depart from the anterior and posterior ends of the ventricle of the heart. The capillaries of the veins and arteries in the skin and muscles pass into each other, and only in some places do lacunar spaces remain; thus, the circulatory system is almost closed. Blood in the air turns blue because it contains hemocyanin (a copper-rich compound, corresponding in physiological functions to vertebrate hemoglobin).
excretory system consists of two or four kidneys, originating from holes in the coelom (pericardial sac). The end products of metabolism come from the gill veins and the pericardial sac and are secreted into the mantle cavity near the anus.
Sexual system. Cephalopods are dioecious animals, in which sexual dimorphism is often well expressed. Sex glands and their ducts are unpaired. Sexual products accumulate in the coelom and are excreted through the genital ducts. Sperm are glued together into spermatophores - packages with a dense shell.
Fertilization usually occurs in the mantle cavity of the female, the role of the copulatory organ is played by one of the tentacles, which in males is distinguished by the presence of a special spoon-shaped appendage. With the help of this tentacle, the male introduces spermatophores into the mantle cavity of the female. All development of the embryos takes place inside the eggs, which the female lays at the bottom. Some cephalopods show concern for offspring: the female argonaut bears eggs in the brood chamber, octopuses guard the laying of eggs.
Subclasses of cephalopods
Modern cephalopods belong to two subclasses: subclass Nautilida (Nautiloidea) and subclass Coleoidei (Coleoidea).
Cephalopods are large in size: from a few centimeters to several meters. It was possible to find a 10-meter tentacle of a cephalopod mollusk. Mollusks live only in the seas and lead a varied lifestyle. Most are pelagic animals living in the water column. In bottom species (part of octopuses), there is a membrane between the tentacles, giving the body of the mollusk the appearance of a disk lying on the bottom. All cephalopods are predators that attack crustaceans and fish, which they seize with tentacles, kill with jaws and poison from the salivary glands.
Many cephalopods are the object of fishing: people use squid, cuttlefish and octopus for food, since their meat has a high nutritional value. The world catch of cephalopods reaches more than 1.6 billion tons per year.
Nautilids include only one order Nautilida, which includes only a few species that live in the tropical regions of the oceans. Nautilids are characterized by many primitive features: an external multi-chamber shell, numerous tentacles without suction cups, a manifestation of metamerism, etc. Nautilus swims in a jet way. It is an object of fishing because of the beautiful shell.
Subclass Coleoidea (Coleoidea) includes about 650 species of hard-skinned molluscs without a shell. They have a fused funnel and tentacles armed with suckers, in addition, they have two gills, two kidneys and two atria.
A characteristic representative of the detachment are cuttlefish (Sepia) having ten tentacles, two of which are agility. They live near the bottom and lead an active swimming lifestyle.
To the Squid squad (Teuthida) include many commercial species ( Todarodes, Loligo etc.) They sometimes retain a rudimentary shell in the form of a horny plate under the skin. Squids have ten tentacles. These are torpedo-shaped inhabitants of the ocean waters.
There are no traces of a shell in the most evolutionarily progressive cephalopods - representatives of the order Octopus (Ostorada). They have eight tentacles, one of which in males is turned into a sexual one. Most octopuses live in the bottom layer of water. Among the octopuses there are representatives that have a brood chamber (argonaut).
Phylogeny of cephalopods
The most ancient representatives of cephalopods are nautilids, whose shells are found in the Cambrian deposits. It is believed that cephalopods evolved from ancient crawling shell molluscs. In the process of evolution, a group of cephalopod mollusks, devoid of a shell, with a new type of jet movement, with a complex nervous system and complex sensory organs, was formed.
From primitive testate benthic-pelagic forms, several paths of ecological specialization were determined. There is a transition to benthic-nekton forms, in which the shell becomes internal and its function as a swimming apparatus weakens, but a new model of mover develops - a funnel. It was they who gave rise to shellless molluscs, which form benthonic-nektonic (cuttlefish, octopus), nektonic (squid, octopus and cuttlefish), benthic and planktonic (umbrella-shaped octopuses, rod-shaped squids) forms of fossils.
Sepia, or cuttlefish ink, is a dark blackish liquid secreted by the cuttlefish cephalopod.
The tincture is made from sepia, which must be obtained in liquid form and dried naturally. Milk sugar rubs are made from the same product.
Pathogenesis Sepia found in Hahnemann's Chronic Diseases.
PHYSIOLOGICAL ACTION
Action Sepia from the very beginning of the experience, it manifests itself in the sympathetic nervous system and mainly in the vasomotors. Indeed, after four hours, there is an increase in blood circulation, flushes to the head, which end in the release of sweat, fainting and loss of strength. At the same time, there is irritation of the nervous system with excitement and sadness.
This is followed by venous congestion. It is especially noticeable in the portal vein system, hence the congestion in the liver and uterus. Congestion of the veins in the extremities causes a painful feeling of weakness, twitching, heaviness, especially noticeable in the thighs, after sleep. There are fainting spells, prostration, general prostration; muscles that are flaccid in themselves relax even more, hence the prolapse of the rectum, the inactivity of the intestines.
This general dysfunction of the body produces visible changes in the skin, which become yellow, earthy.
The mucous membranes are also affected: the discharge is always mucopurulent, greenish-yellow, not irritating; due to irritation of the mucous membrane of the urinary tract, diseases of the urethra with pain and bladder are observed; irritation of the mucous membrane of the respiratory tract causes a dry incessant cough, aggravated by cold. Later comes the discharge of greenish-yellow sputum, as in the early stages of consumption. There is also a flaccid chronic catarrh of the nose with profuse green and yellow discharge, as in Pulsatilla, but the action Sepia deeper - bones can often be affected, as in lakes.
TYPE
Type Sepia with sickly sallow complexion; on the face, mainly on the bridge of the nose, in the form of a saddle, there are yellow spots that are also found on the whole body. Blue under the eyes, black hair, slender figure. Such subjects, both men and women, are prone to sweating. They suffer from hot flashes, headache in the morning, wake up feeling tired. There is almost always some kind of disease in the genitals. Both sexes have congestive liver, atonic dyspepsia, constipation.
Physical type Sepia never has a strong, healthy appearance, good health, but on the contrary, impotence, general weakness, pale color of the connective membranes.
Mentally subject Sepia- and this is most often a woman - always sad for no reason; seeks solitude, avoids society, cries without any reason on the sly. Everything is boring for him, things are disgusting to him, and he is not at all interested in them; family and even children are completely indifferent to him.
Sadness is replaced by periods of excitement, during which the patient becomes irritable. Attacks of involuntary tears and laughter are often observed.
PECULIARITIES
Worse: morning and evening, new and full moon.
Improvement: after noon.
Dominant side: left.
CHARACTERISTIC
Feeling of heaviness and pressure on the bottom, as if all the contents of the abdominal cavity want to go out through the vagina, as a result of this, a characteristic posture: the patient crosses her legs with force or presses on the vagina with her hand.
Yellow patches, hepatic, particularly visible on the face, cheeks and nose, where they are butterfly or saddle shaped.
Abrasions and eczema on the folds of almost all joints.
Rigor and heaviness in the thighs, especially after sleep.
Weakness in the joints that disappears when walking; looks like they are about to pop out.
Sensation of a foreign body, bullets, in various parts of the body, especially in the rectum.
Every collar seems narrow; the patient stretches it ( Lachesis).
Foul-smelling perspiration, chiefly under the armpits and in the popliteal pits.
Mucopurulent discharge, yellowish green and non-irritating, similar to Pulsatilla.
Vomiting and nausea, easily coming on under the influence of the slightest physical or moral influence.
Food seems too salty Pulsatilla vice versa.
Pain. pain Sepia are often at rest, and movement never improves them. They are worst at night, accompanied by numbness of the affected part, they are worse from cold and better after dinner.
The chair is hard, knotty, balls, insufficient, difficult. Pain in rectum during and long after stool.
Menses are irregular, unlike one another, most often late and scanty. Colic before menses. During them, pressure on the bottom, the need to cross the legs.
MAIN INDICATIONS
Wherever there is a disease requiring a prescription Sepia, according to Test, it can be said for sure that it is always accompanied by known organic or functional disorders of the genital organs.
The consequences of venous stasis in the uterus can be:
LOSS AND DISPLACEMENT OF THE UTERUS.
BELI against which Sepia often the best remedy; they are yellow, green, with severe itching.
STOPPING AND TOO HEAVY MENTIONS are indifferently cured Sepia, unless they depend on venous congestion in the uterus.
It is the best remedy for gonorrhea in women, after the acute symptoms have disappeared.
Venous stasis in the abdominal cavity causes from the intestines:
PROLONGATION OF THE RECTUM.
HEMORRHOIS: bleeding in stool, with feeling of fullness in the rectum, as if distended by some foreign body, which causes urging.
DYSPEPSIA with empty and sinking feeling in the stomach, weakness in the pit of stomach and in the abdomen, with a normal or bitter taste in the mouth; the need for sour and seasonings; bloating. The patient easily vomits (when brushing his teeth, from the smell of food, when receiving unpleasant news, etc.).
Sensitivity in the region of the liver.
Does not tolerate milk, it produces a sour eructation.
Dyspepsia of smokers.
MIGRAINE with throbbing pains over the eye (usually over the left).
Gouty headache, worse in the morning with nausea and vomiting (the liver is naturally affected and the urine is saturated with uric acid). Shooting pains over left eye, in vertex and occiput. Very intense pain, sometimes like a blow, when shaking the head.
ECZEMA on the head and on the face, on the folds of the joints, in the vagina and anus. Dry scaly crusts, firmly seated and separated with great difficulty in the presence of uterine disorders, indicate mainly Sepia. The rash periodically gets wet. It often takes on a round or annular shape, especially at the folds of the joints. Worse during and after menses, from warmth in bed. Skin diseases are often replaced by uterine disorders.
BRONCHITIS: expectoration of dirty, salty tasting sputum.
Lack of strength, worse in the evening, ptosis. Sudden loss of vision.
DOSES
Most often, medium and high dilutions are used. Low rubbing is useful in diseases of the throat, uterus and skin. With leucorrhoea, a first decimal rub of five centigrams twice a day is often necessary, according to Piedvas.
SUMMARY
Wherever there is a disease, one can certainly say that it is always accompanied by known overt or latent organic or functional diseases in the genital area. Already Hippocrates used Sepia in women's diseases. Sepia called "washerwomen's medicine", many illnesses are caused or aggravated by work in the laundry. Venous congestion in the portal vein, with painful disorders of the liver and uterus.