Female infidelity is a rather complex phenomenon. First, with the social ...
The body of cephalopods is bilaterally symmetrical, divided into a head and a trunk. The leg transformed into tentacles and a funnel. The shell in primitive forms is external, multi-chambered (Nautilus pompilius), in higher representatives it is an internal reduced, often absent. On the head is a mouth surrounded by tentacles and large eyes. Most species have suckers on the tentacles.
rice. 1. Diagram of the structure of an octopus:
1 - gill, 2 - gill heart, 3 - kidney, 4 - heart,
5 - sex gland, 6 - intestines, 7 - stomach,
8.9 - ink sacs, 10 - pancreas,
11 - mantle muscles, 12 - liver, 13 - goiter,
14 - poisonous gland, 15 - skull, 16 - brain,
17 - head vein, 18 - pharyngeal muscles,
19 - tentacle nerves, 20 - beak, 21 - funnel.
The integument is represented by a single layer of epithelium and a layer of connective tissue. In the skin there are pigment cells - chromatophores, thanks to which the cephalopods can quickly change the color of the body.
The anal, genital and excretory openings open into the mantle cavity located on the abdominal side. To move quickly, cephalopods use a reactive method: with the help of strong muscle contractions, they throw water through a funnel from the mantle cavity, recoil pushes the body in the opposite direction.
Cephalopods are predators. They feed on fish, crustaceans, molluscs, etc. The prey is seized by tentacles and killed by hard horny jaws and poison. There is a tongue with a radula in the throat. The ducts of 1-2 pairs of salivary glands flow into the pharynx, which secrete enzymes that break down proteins and polysaccharides. The second posterior pair of salivary glands secretes poison. The esophagus passes through the brain, so there should be no large particles in the food gruel. The stomach follows the esophagus, small intestine, the hind gut ending in the anus. The ducts of the liver and "pancreas" flow into the stomach. The duct of the ink sac opens into the hind gut. His secret is thrown out in case of danger through the anus. The “ink” forms a kind of smoke screen in the water, allowing the cephalopod to escape from the pursuer.
Respiratory organs are represented by true gills (ctenidia) located in the mantle cavity on the sides of the body.
In the circulatory system there is a heart, consisting of a ventricle and atria (two or four), in addition there are two so-called "gill hearts", which, rhythmically contracting, push blood through the gills. The oxidized blood returns to the heart. Blood contains the respiratory pigment hemocyanin, which contains copper. When oxidized, such blood "turns blue".
The excretory system consists of two or four kidneys. Their inner ends open into the pericardium, and the outer holes open into the mantle cavity.
The nervous system in cephalopods is the most highly organized among all invertebrates. The ganglia form a common periopharyngeal nerve mass, protected by a cartilaginous "skull". The sense of smell is well developed. The organs of vision are represented by large, complexly arranged eyes that are capable of accommodation. Unlike the human eye, accommodation is carried out not by changing the curvature of the lens, but by the approach or removal of the lens relative to the retina.
rice. 2. Ammonite
(reconstruction)
rice. 3.
A - sink,
B - appearance
(reconstruction):
1 - rostrum.
Cephalopods are dioecious. Fertilization takes place in the mantle cavity of the female. Direct development. Some species take care of the offspring.
The class Cephalopods is divided into two subclasses: Nautiloidea, Coleoidae.
Cephalopods appeared in the Cambrian period of the Paleozoic era. The first cephalopods had an external straight shell, divided into chambers. The length of such shells reached 4-5 m. Ammonites have been known since the Devonian period of the Paleozoic era (Fig. 2). Ammonites possessed a spirally twisted multichamber shell, the revolutions of which were in the same plane. The diameter of ammonite shells reached 2 m. In the Cretaceous period of the Mesozoic era, ammonites died out. Ammonites were among the most abundant animals of the Mesozoic era, and their fossil shells serve as guiding forms in geology for determining the age of strata. Belemnites appeared in the Triassic of the Mesozoic era. They resembled modern squid in body shape (Fig. 3). But their inner shell was conical and multi-chambered. The terminal rostrum of their shells, which can be found in geological deposits, are called "devil's fingers". The body length of some belemnite species reached several meters. Belemnites were widespread in the Jurassic period of the Mesozoic era and became completely extinct by the middle of the Paleogene of the Cenozoic era. In the Cretaceous period of the Mesozoic era, coleoids appear, with a complex nervous system and sensory organs, with reactive motion, with an internal reduced shell. Coleoids are at their peak by now.
Description of classes, subclasses and units of the Mollusks type:
Class Gastropoda
Topic: "Cephalopods".
Target: to study the features of the structure and life of cephalopods.
Tasks:
Educational: to form knowledge about the biological role of mollusks, their practical significance for humans, to study the characteristics of the vital activity of animals of this class.
Educational: ecological education.
Developing: develop memory, thinking, imagination.
Type of: combined.
Methods: verbal, visual.
Funds: drawings, equipment, slides.
The form: frontal, group, individual.
Plan
Cephalopod habitats.
External and internal structure of cephalopods (for example, an octopus).
Practical significance.
Students' performance in groups: group 1 - squid, group 2 - cuttlefish.
The sizes of cephalopods are very different. Among them there are dwarfs, such as cuttlefish whose mantle length is less than 1 cm, and there are giants, among which, first of all, squid, the length of their body together with tentacles can reach 18 m.
The following is the teacher's story about the structure and characteristics of the octopus. In parallel, students write down the reference points in a notebook.
Cephalopods are bilaterally symmetrical animals with an external or internal shell. In cuttlefish, it looks like a plate lying under the mantle and, like a shield, covering the body of the mollusk from the back. In squid, the shell looks like a thin transparent plate, shaped like a Roman sword. In octopuses, from the shells, and even then not in all, cartilaginous formations in the form of rods or curved plates supporting the fins remained.
In cuttlefish, the body is flattened, in squid it is cylindrical, pointed towards the posterior end, fusiform or conical; in octopuses, it is saccular. In all cephalopods, the body is clothed with a skin-muscular bag - a mantle that encloses the internal organs. On the sides of the mantle of squid, cuttlefish, octopus fins are located, which come in a wide variety of shapes and sizes and serve as mollusks for swimming and as rudders.
So the body consists of a torso and a head.
Digestive system: The pharynx is muscular, with two strong jaws resembling the beak of a parrot and called the "beak". The ducts of the poisonous salivary glands flow into it. In the oral cavity, on a special lingual protrusion, a radula is placed, seated in rows of small denticles. With the help of the radula, food that has entered the mouth of the mollusk and moistened with saliva is transported further into the esophagus. Bottom octopuses use a very strong radula to drill through the shells of bivalve and gastropod molluscs and to scoop out pieces of meat from under the shells of caught crabs. A thin tube stretches from the pharynx to the stomach - the esophagus, piercing the brain and liver on the way to the stomach. Therefore, the cephalopods, despite their great appetite, cannot swallow the prey whole, but are forced to crush it into small pieces with their “beak” before sending it into their mouth. The pieces of food eaten then enter the gizzard, where the digestive juices produced by the liver and pancreas enter. The enzyme activity of these glands is very high, and food is digested in 4 hours. Undigested food debris enters the intestine and is thrown out. The liver performs several functions - it produces digestive enzymes, amino acids are absorbed in it, it is also a storehouse of spare nutrients... On the ventral side is an ink sac with a duct that flows into the intestine. Most cephalopods have an ink sac.
Respiratory system: They breathe with the help of gills (one or two pairs located in the mantle cavity).
Circulatory system: The circulatory system is almost closed, there are additional branchial hearts that increase blood flow. The blood is set in motion by three hearts: the main one, consisting of a ventricle and two atria, and two branchials. The heart rate of an octopus reaches 50 beats per minute. The skin and muscles have capillaries. The blood of cephalopods is blue due to the presence of the respiratory pigment hemocyanin, which contains copper.
Excretory system: The organs of excretion are the renal sacs, the appendages of the gill hearts, the gills themselves.
Nervous system: The central nervous system in the form of a complex brain, surrounded by a cartilaginous cranial capsule. The ganglia are very close together and form a large brain. 2 large nerves branch off from it.
Senses: On the head are large complex eyes. Their sense organs are highly developed. The eyes of cephalopods resemble fish eyes in terms of their complexity, and in terms of visual acuity they are not inferior to human eyes. The eyes are usually placed in the recesses of the cartilaginous head capsule and have a cornea, an iris with a pupil capable of constricting and dilating, a lens and a retina. There is even an eyelid that can close the eye, in addition to the organ of vision, there are organs of chemical sense, balance, tactile cells, photosensitive and gustatory.
Reproductive system, reproduction. Divided. Direct development.
Drawing up a reference circuit:
Features of cephalopods:
horny jaws.
poisonous salivary glands.
ink bag.
brain
eyes
almost closed circulatory system.
dioecious.
Reflection: performing an interactive task (Frontal)
Which of the named molluscs belongs to the class Cephalopods:
2. Octopuses and squids move with the help of:
A. Legs. B. Legs and tentacles. B. Reactive motion. D. Water currents.
3. The most highly developed among molluscs are:
A. Squid. B. Perlovitsa. V. Midia. G. Snail.
4. An ink gland is available for:
A. All molluscs. B. Cephalopods. V. Gastropods. G. Bivalves.
5. Which molluscs have the brain enclosed in a capsule:
A. Oysters. B. Prudoviki. B. Octopuses. G. Slugs.
Correct answers: 1D, 2B, 3a, 4B, 5C.
Self-control, assigning marks for work.
5. Homework: repeat the Molluscs theme, prepare for independent work.
Class Cephalopods (Cephalopoda)
Cephalopods are the most highly organized molluscs. They are rightly called the "primates" of the sea among invertebrates for the perfection of their adaptations to life in the marine environment and the complexity of their behavior. These are mainly large carnivorous marine animals that can actively swim in the water column. These include squid, octopus, cuttlefish, nautilus (Fig. 234). Their body consists of a torso and a head, and the leg is transformed into tentacles located on the head around the mouth, and a special motor funnel on the ventral side of the body (Fig. 234, A). Hence the name - cephalopods. It has been proven that part of the tentacles of cephalopods is formed at the expense of the cephalic appendages.
In most modern cephalopods, the shell is absent or rudimentary. Only the genus Nautilus (Nautilus) has a spirally twisted shell, divided into chambers (Fig. 235).
Only 650 species belong to modern cephalopods, and there are about 11 thousand fossil species. This is an ancient group of mollusks, known from the Cambrian. Extinct species of cephalopods were predominantly concha and had an external or internal concha (Fig. 236).
For cephalopods, many progressive organizational features are characteristic due to the active lifestyle of marine predators. At the same time, they retain some primitive features that testify to their ancient origin.
External structure... Features of the external structure of cephalopods are varied in connection with a different way of life. Their sizes range from a few centimeters to 18 m in some squid. Nectonic cephalopods are usually torpedo-shaped (most squid), benthic cephalopods have a bag-shaped body (many octopuses), nektobenthos - flattened (cuttlefish). Planktonic species are small in size and have a gelatinous floating body. The body shape in planktonic cephalopods can be narrow or jellyfish-like, and sometimes spherical (squid, octopus). Bentopelagic cephalopods have a shell divided into chambers.
The body of a cephalopod consists of a head and torso. The leg is modified into tentacles and a funnel. On the head is a mouth surrounded by tentacles and large eyes. The tentacles are formed by the cephalic appendages and the leg. These are the organs for capturing food. The primitive cephalopod (Nautilus) has an indefinite number of tentacles (about 90); they are smooth, worm-like. In higher cephalopods, the tentacles are long, with powerful muscles and bear large suckers on the inner surface. The number of tentacles is 8-10. Cephalopods with 10 tentacles have two tentacles - trapping, longer, with suckers at widened ends,
Rice. 234. Cephalopods: A - nautilus Nautilus, B - octopus Benthoctopus; 1 - tentacles, 2 - funnel, 3 - hood, 4 - eye
Rice. 235. Nautilus Nautilus pompilius with a sawn shell (according to Owen): 1 - head hood, 2 - tentacles, 3 - funnel, 4 - eye, 5 - mantle, 6 - internal sac, 7 - chambers, 8 - partition between shell chambers, 9 - siphon
Rice. 236. Diagram of the structure of cephalopod shells in the sagittal section (from Gescheler): A - Sepia, B - Belosepia, C - Belemnites, D - Spirulirostra, E - Spirula, E - Ostracoteuthis, F - Ommastrephes, H - Loligopsis (C, D, E - fossils); 1 - proostracum, 2 - dorsal edge of the siphonal tube, 3 - ventral edge of the siphonal tube, 4 - set of chambers-phragmocon, 5 - rostrum, 6 - siphon cavity
Rice. 237. Cuttlefish mantle cavity - Sepia (according to Pfurscheller): 1 - short tentacles, 2 - trapping tentacles, 3 - mouth, 4 - funnel opening, 5 - funnel, 6 - cartilaginous fossa of cufflinks, 7 - anus, 8 - renal papillae, 9 - genital papilla, 10 - gills, 11 - fin, 72 - cutting line of the mantle, 13 - mantle, 14 - cartilaginous tubercles of cufflinks, 15 - mantle ganglion
and the other eight tentacles are shorter (squid, cuttlefish). Octopuses living on the seabed have eight tentacles of the same length. They serve the octopus not only to grab food, but also to move along the bottom. In male octopuses, one tentacle is modified into a sexual one (hectocotyl) and serves to transfer the reproductive products into the mantle cavity of the female.
The funnel is a derivative of the leg in cephalopods, it serves for the "reactive" mode of movement. Through the funnel, water is forcefully pushed out of the mantle cavity of the mollusk, and its body moves reactively in the opposite direction. In a boat, the funnel has not grown together on the ventral side and resembles the sole of the foot of crawling mollusks rolled into a tube. Evidence that the tentacles and funnel of cephalopods are derived from the legs is their innervation from the pedal ganglia and the embryonic anlage of these organs on the ventral side of the embryo. But, as already noted, some of the tentacles of the cephalopods are derivatives of the cephalic appendages.
The mantle on the ventral side forms a kind of pocket - a mantle cavity, opening outward with a transverse slit (Fig. 237). A funnel protrudes from this gap. On the inner surface of the mantle there are cartilaginous protrusions - cufflinks that fit tightly into the cartilaginous depressions on the body of the mollusk, and the mantle is, as it were, fastened to the body.
The mantle cavity and funnel together provide jet propulsion. When the musculature of the mantle relaxes, water enters through the gap into the mantle cavity, and when it contracts, the cavity closes with cufflinks and the water is pushed out through the funnel. The funnel is able to bend to the right, left and even back, which provides a different direction of movement. The role of the rudder is additionally performed by the tentacles and fins - the skin folds of the trunk. The types of movement in cephalopods are varied. Octopuses move more often on tentacles and swim less often. In cuttlefish, in addition to the funnel, a circular fin serves for movement. Some deep-sea umbellate octopuses have a membrane between the tentacles - umbrella and can move due to its contractions, like jellyfish.
The shell in modern cephalopods is rudimentary or absent. In ancient extinct cephalopods, the shell was well developed. Only one modern genus, Nautilus, has retained a developed shell. The Nautilus shell in fossil forms also has significant morphological and functional features, in contrast to the shells of other mollusks. It is not only a protective device, but also a hydrostatic apparatus. In the Nautilus, a spirally wound shell is divided by partitions into chambers. The body of the mollusk is placed only in the last chamber, which opens outward with the mouth. The rest of the chambers are filled with gas and chamber liquid, which ensures the buoyancy of the mollusk body. Across
a siphon, the posterior process of the body, passes through the holes in the partitions between the shell chambers. The cells of the siphon are capable of producing gases. When surfacing, the mollusk releases gases, displacing the chamber liquid from the chambers; when lowering to the bottom, the mollusk fills the shell chambers with chamber liquid. The mover of the Nautilus is a funnel, and the shell keeps its body suspended in water. Fossil nautilids had a shell similar to that of the modern nautilus. The completely extinct cephalopods - ammonites also had an outer, spirally twisted shell with chambers, but their partitions between the chambers had a wavy structure, which increased the strength of the shell. That is why ammonites could reach very large sizes, up to 2 m in diameter. Another group of extinct cephalopods, the Belemnoidea, had an inner shell overgrown with skin. Belemnites in appearance resembled shellless squids, but in their body there was a conical shell, divided into cameras. The apex of the shell ended with a point - the rostrum. The rostrum of belemnite shells are often found in the Cretaceous deposits, and they are called "devil's fingers". Some modern shellless cephalopods have rudiments of an inner shell. So, in cuttlefish on the back under the skin, a calcareous plate is preserved, which has a chamber structure on the cut (238, B). Only in Spirula (Spirula) under the skin there is a fully developed spirally twisted shell (Fig. 238, A), and in the squid, under the skin, only the horny plate is preserved from the shell. The females of modern cephalopods - Argonauts (Argonauta) have a developed brood chamber resembling a spiral shell in shape. But this is only an external resemblance. The brood chamber is distinguished by the epithelium of the tentacles, is very thin and is designed to protect the developing eggs.
Veils... The skin is represented by a single layer of epithelium and a layer of connective tissue. The skin contains pigment cells - chromatophores. Cephalopods are characterized by the ability to quickly change color. This mechanism is controlled by the nervous system and is carried out by changing the shape
Rice. 238. Shell rudiments in cephalopods (according to Natalie and Dogel): A - Spirula; 1 - funnel, 2 - mantle cavity, 3 - anus, 4 - excretory opening, 5 - organ of luminescence, 6 - fin, 7 - shell, 8 - siphon; B - Sepia shell; 1 - septa, 2 - lateral edge, 3 - siphonal fossa, 4 - rostrum, 5 - siphon rudiment, 6 - posterior edge of proostracum
pigment cells. So, for example, cuttlefish, swimming over sandy ground, takes on a light color, and over rocky ground - dark. At the same time, in her skin, pigment cells with dark and light pigments alternately shrink and expand. If you cut the optic nerves in a mollusk, then it loses its ability to change color. Due to the connective tissue of the skin, cartilage is formed: in the cufflinks, the bases of the tentacles, around the brain.
Protective devices... Cephalopods, having lost their shell in the process of evolution, acquired other protective devices. First, fast movement saves many of them from predators. In addition, they can defend themselves with tentacles and a "beak" that is modified jaws. Large squids and octopuses can fight large marine animals such as sperm whales. In sedentary and small forms, a protective coloration and the ability to quickly change color are developed. Finally, some cephalopods, such as the cuttlefish, have an ink sac, the duct of which opens into the hindgut. Spraying the ink liquid into the water creates a kind of smokescreen that allows the mollusk to hide from predators to a safe place. Cuttlefish ink gland pigment is used to make high quality artistic ink.
Internal structure of cephalopods
Digestive system cephalopods have features of specialization for feeding on animal food (Fig. 239). They are mainly fed by fish, crabs and bivalve molluscs. They seize prey with tentacles and kill with jaws and poison. Despite their large size, cephalopods can only eat liquid food, since they have a very narrow esophagus that passes through the brain, enclosed in a cartilaginous capsule. Cephalopods have devices for grinding food. For gnawing prey, they are served by hard horny jaws, similar to the beak of a parrot. In the throat, food is rubbed with radula and abundantly moistened with saliva. The ducts of 1-2 pairs of salivary glands flow into the pharynx, which secrete enzymes that break down proteins and polysaccharides. The second posterior pair of salivary glands secretes poison. Liquid food from the pharynx through the narrow esophagus enters the endodermal stomach, where the ducts of the paired liver flow, which produces a variety of digestive enzymes. The hepatic ducts are seated with small additional glands, the aggregate of which is called the pancreas. The enzymes of this gland act on polysaccharides,
and, therefore, this gland is functionally different from the mammalian pancreas. The stomach of cephalopods is usually with a blind sac-shaped process that increases its volume, which allows them to absorb a large portion of food. Like other carnivorous animals, they eat a lot and relatively rarely. The small intestine departs from the stomach, which then passes into the back, which opens with the anus into the mantle cavity. In many cephalopods, the duct of the ink gland flows into the hind gut, the secret of which has a protective value.
Nervous system cephalopods are the most highly developed among molluscs. The nerve ganglia form a large periopharyngeal accumulation - the brain (Fig. 240), enclosed in a cartilaginous capsule. There are additional ganglia. The composition of the brain primarily includes: a pair of large cerebral ganglia that innervate the head, and a pair of visceral ganglia that send nerve cords to the internal organs. On the sides of the cerebral ganglia there are additional large optical ganglia that innervate the eyes. Long nerves extend from the visceral ganglia to two stellate-shaped mantle ganglia that develop in cephalopods in connection with the function of the mantle in their reactive mode of movement. In addition to cerebral and visceral, the cephalopod brain includes pedal ganglia, which are subdivided into paired ganglia of tentacles (brachial) and funnels (infudibular). A primitive nervous system, similar to the ladder system of the lateral nerves and monoplacophores, is preserved only in Nautilus. It is represented by nerve cords forming a periopharyngeal ring without ganglia and a pedal arch. The nerve cords are covered with nerve cells. This structure of the nervous system testifies to the ancient origin of cephalopods from primitive shell molluscs.
Sense organs the cephalopods are well developed. Eyes, which are of the greatest importance for orientation in space and hunting for prey, reach especially complex development. In Nautilus, the eyes have a simple structure in the form of a deep eye fossa (Fig. 241, A), and in the rest of the cephalopods, the eyes are complex, in the form of an eye bladder and resemble the structure of the eye in mammals. This is an interesting example of convergence between invertebrates and vertebrates. Figure 241, B shows the eye of a cuttlefish. The top of the eyeball is covered with the cornea, which has an opening into the anterior chamber of the eye. The connection of the anterior cavity of the eye with the external environment protects the eyes of the cephalopods from action high pressure at great depths. The iris forms an opening - the pupil. Light through the pupil enters the spherical lens formed by the epithelial body - the upper shell of the optic bladder. The accommodation of the eye in cephalopods is different,
Rice. 239. Digestive system of cuttlefish Sepia officinalis (according to Reseller and Lamprecht): 1 - pharynx, 2 - common salivary duct, 3 - salivary ducts, 4 - posterior salivary gland, 5 - esophagus, 6 - head aorta, 7 - liver, 8 - pancreas, 9 - stomach, 10 - blind sac of the stomach, 11 - small intestine, 12 - hepatic duct, 13 - rectum, 14 - ink sac duct, 15 - anus, 16 - head cartilaginous capsule (cut), 17 - statocyst , 18 - nerve ring (cut)
Rice. 240. Nervous system of cephalopods: 1 - brain, 2 - optic ganglia, 3 - mantle ganglia, 4 - intestinal ganglion, 5 - nerve cords in the tentacles
Rice. 241. Eyes of cephalopods: A - Nautilus, B - Sepia (according to Gensen); 1 - cavity of the eye fossa, 2 - retina, 3 - optic nerves, 4 - cornea, 5 - lens, 6 - anterior chamber of the eye, 7 - iris, 8 - ciliary muscle, 9 - vitreous body, 10 - ocular processes of the cartilaginous capsule, 11 - optical ganglion, 12 - sclera, 13 - eye chamber holes, 14 - epithelial body
than in mammals: not by changing the curvature of the lens, but by bringing it closer or moving away from the retina (like focusing a camera). Special ciliary muscles fit the lens, which set it in motion. The cavity of the eyeball is filled with the vitreous body, which has a refractive function. The bottom of the eye is lined with visual - retinal and pigment - cells. This is the retina of the eye. A short optic nerve departs from it to the optic ganglion. The eyes, together with the optic ganglia, are surrounded by a cartilaginous capsule. Deep-sea cephalopods have organs of luminescence on their bodies, built according to the type of eyes.
Balance organs- statocysts are located in the cartilaginous capsule of the brain. The olfactory organs are represented by the olfactory pits under the eyes or osphradia typical of mollusks at the base of the gills - in the nautilus. The organs of taste are concentrated on the inner side of the ends of the tentacles. Octopuses, for example, use their tentacles to distinguish edible objects from inedible ones. The skin of cephalopods contains many tactile and light-sensitive cells. In search of prey, they are guided by a combination of visual, tactile and gustatory sensations.
Respiratory system represented by ctenidia. Most modern cephalopods have two, while the Nautilus has four. They are located in the mantle cavity on the sides of the body. The flow of water in the mantle cavity, which ensures gas exchange, is determined by the rhythmic contraction of the muscles of the mantle and the function of the funnel through which water is pushed out. During the reactive mode of movement, the flow of water in the mantle cavity is accelerated, and the intensity of respiration increases.
Circulatory system the cephalopods are almost closed (Fig. 242). In connection with active movement, the whole and blood vessels are well developed in them and, accordingly, parenchymal is poorly expressed. Unlike other mollusks, they do not suffer from hypoenia - poor mobility. The speed of blood flow in them is ensured by the work of a well-developed heart, consisting of a ventricle and two (or four - in Nautilus) atria, as well as pulsating sections of blood vessels. The heart is surrounded by an extensive pericardial cavity,
Rice. 242. The circulatory system of cephalopods (from Abrikosov): 1 - heart, 2 - aorta, 3, 4 - veins, 5 - gill vessels, 6 - gill hearts, 7, 8 - renal portal system, 9 - gill veins
which performs many functions of the coelom. From the ventricle of the heart, the head aorta - forward and the internal aorta - backward. The head aorta branches into arteries that supply blood to the head and tentacles. Vessels depart from the internal aorta to the internal organs. Blood from the head and internal organs collected in the vena cava, located longitudinally in the lower body. The vena cava is subdivided into two (or four in Nautilus) bearing gill vessels, which form contracting enlargements - gill "hearts" that promote gill circulation. The bearing gill vessels adjoin closely to the kidneys, forming small blind invaginations into the kidney tissue, which facilitates the release of venous blood from metabolic products. In the branchial capillaries, the blood is oxidized, which then enters the efferent branchial vessels, which flow into the atria. Partially, the blood from the capillaries of the veins and arteries flows into small lacunas, and therefore the circulatory system of the cephalopods should be considered almost closed. The blood of cephalopods contains a respiratory pigment - hemocyanin, which contains copper, therefore, when oxidized, the blood turns blue.
Excretory system represented by two or four (in Nautilus) buds. With the inner ends, they open into the pericardial sac (pericardium), and the outer ends - into the mantle cavity. Excretion products enter the kidneys from the branchial veins and from the extensive pericardial cavity. Additionally, the excretory function is performed by the pericardial glands formed by the wall, the pericardium.
Reproductive system, reproduction and development... Cephalopods are dioecious animals. In some species, sexual dimorphism is well pronounced, for example, in the Argonauta. The female Argonaut is larger than the male (Fig. 243) and during the breeding season it secretes around the body with the help of special glands on the tentacles a thin-walled parchment-like brood chamber for bearing eggs, similar to a spiral shell. The male Argonaut is several times smaller than the female and has a special elongated sexual tentacle, which is filled with sexual products during the breeding season.
The gonads and reproductive ducts are unpaired. An exception is the nautilus, which has preserved paired ducts extending from the unpaired gonad. In males, the vas deferens passes into the spermatophore bag, where the spermatozoa are glued together in special packages - spermatophores. In cuttlefish, the spermatophore has the shape of a checker; its cavity is filled with spermatozoa, and the outlet is closed with a complex plug. During the breeding season, the male cuttlefish transfers the spermatophore into the mantle cavity of the female using a genital tentacle with a spoon-shaped end.
Rice. 243. Argonauta mollusk: A - female, B - male; 1 - funnel, 2 - eye, 3 - shell, 4 - hectocotyl, 5 - funnel, 6 - eye (according to Dogel)
Cephalopods usually lay their eggs at the bottom. In some species, care for the offspring is observed. So, the female Argonaut bears eggs in the brood chamber, and the octopuses guard the eggs, which are placed in shelters made of stones or in caves. Direct development, without metamorphosis. Small, fully formed cephalopods emerge from the eggs.
Modern cephalopods belong to two subclasses: the Nautiloidea subclass and the Coleoidea subclass. Extinct subclasses include: the Ammonoidea subclass, the Bactritoidea subclass, and the Belemnoidea subclass.
Nautiloidea subclass
Modern nautilids include one order, the Nautilida. It is represented by only one genus Nautilus, to which only a few species belong. The distribution area of Nautilus is limited to the tropical regions of the Indian and Pacific Oceans. There are more than 2500 species of nautilid fossils. This is an ancient group of cephalopods, known from the Cambrian.
Nautilids have many primitive features: the presence of an external multi-chambered shell, a non-accrete funnel, numerous tentacles without suction cups, a manifestation of metamerism (four ctenidia, four kidneys, four atria). The similarity of nautilides with lower shell molluscs is manifested in the structure of the nervous system from cords without separate ganglia, as well as in the structure of coelomoducts.
Nautilus belongs to the benthopelagic cephalopods. It floats in the water column in a "reactive" way, pushing water out of the funnel. The multichamber shell ensures the buoyancy of its body and sinking to the bottom. Nautilus has long been an object of fishing because of its beautiful mother-of-pearl shell. Nautilus shells are used to make many exquisite jewelry.
Coleoidea subclass
Coleoidea means "tough" in Latin. These are hard-skinned molluscs without shells. Coleoids are a thriving group of modern cephalopods, comprising four orders, which include about 650 species.
The general features of the subclass are: the absence of a developed shell, an accrete funnel, tentacles with suction cups.
Unlike nautilide, they only have two ctenidia, two kidneys, and two atria. Coleoidea have a highly developed nervous system and sense organs. The following three orders are characterized by the largest number of species.
Detachment Cuttlefish (Sepiida). The most characteristic representatives of the order are cuttlefish (Sepia) and spirula with rudiments of an inner shell. They have 10 tentacles, two of which are hunters. These are non-benthic animals, they stay at the bottom and are able to actively swim.
Squid squad (Teuthida). This includes many commercial squids: Todarodes, Loligo, etc. Squids sometimes retain a rudiment
shells in the form of a smooth plate under the skin on the back. They have 10 tentacles, just like the previous unit. These are mainly nekton animals, actively swimming in the water column, having a torpedo-shaped body (Fig. 244).
Squad Eight-legged (Octopoda). This is an evolutionarily advanced group of cephalopods without traces of a shell. They have eight tentacles. Sexual dimorphism is pronounced. Males develop a genital tentacle - hectocotyl. This includes a variety of octopuses (Fig. 245). Most octopuses are benthic. But among them there are nektonous and even planktonic forms. The genus Argonauta, an Argonaut, belongs to the order Octopoda, in which the female selects a special brood chamber.
Rice. 244. Squid Loligo (from Dogel)
Rice. 245. Octopus (male) Ocythoe (according to Pelsner): 1 - tentacles, 2 - funnel, 3 - hectocotyl, 4 - pouch, 5 - filament
The practical value of cephalopods
Cephalopods are game animals. Meat of cuttlefish, squid and octopus is used for food. The world catch of cephalopods currently reaches more than 1600 thousand tons. in year. Cuttlefish and some octopuses are also harvested for the purpose of obtaining ink liquid, from which natural ink and ink of the highest quality are made.
Paleontology and phylogeny of cephalopods
The most ancient group of cephalopods is considered the nautilid, the fossil shells of which are already known from the Cambrian deposits. The primitive nautilids had a low conical shell with only a few chambers and a wide siphon. It is assumed that the cephalopods evolved from ancient crawling shell molluscs with a simple conical shell and a flat bottom, like some fossil monoplacophores. Apparently, a significant aromorphosis in the emergence of cephalopods consisted in the appearance of the first septa and chambers in the shell, which initiated the development of a hydrostatic apparatus in them and determined the possibility of floating up, breaking away from the bottom. Apparently, the formation of the funnel and tentacles took place in parallel. The shells of the ancient nautilids were varied in shape: long conical and flat, spirally twisted with a different number of chambers. Among them there were also giants up to 4-5 m (Endoceras), which led a near-bottom lifestyle. Nautilids have undergone several periods of prosperity and extinction in the process of historical development and have existed to this day, although they are now represented by only one genus Nautilus.
In the Devonian, in parallel with nautilids, a special group of cephalopods begins to occur - bactrites (Bactritoidea), smaller in size and less specialized than nautilids. It is assumed that this group of cephalopods descended from common as yet unknown ancestors with the nautilids. Bactrites turned out to be an evolutionarily promising group. They gave rise to two branches of the development of cephalopods: ammonites and belemnites.
The subclass of ammonites (Ammonoidea) appeared in the Devonian and became extinct at the end of the Cretaceous. During the heyday, the ammonites successfully competed with the nautilids, whose numbers were declining noticeably at that time. It is difficult for us to judge the advantages of the internal organization of ammonites from fossil shells alone. But the shell of the ammonites was more perfect
Rice. 246. Fossil cephalopods: A - ammonite, B - belemnite
than nautilide: lighter and more durable. The partitions between the chambers in the ammonites were not smooth, but wavy, and the lines of partitions on the shell were zigzag, which increased the strength of the shell. The ammonite shells were spirally twisted. More often, the spiral turns of ammonite shells were located in the same plane, and less often they had the shape of a turbo spiral (Fig. 246, A). According to some footprints of the body of fossil remains of ammonites, it can be assumed that they had up to 10 tentacles, possibly two ctenidia, beak-like jaws, and an ink sac. This indicates that, apparently, oligomerization of metameric organs took place in ammonites. According to paleontological data, ammonites were ecologically more diverse than nautilids, and nekton, benthic, and planktonic forms were found among them. Most of the ammonites were small in size, but there were also giants with shells up to 2 m in diameter. Ammonites were one of the most numerous marine animals in the Mesozoic, and their fossil shells serve as guiding forms in geology for determining the age of strata.
Another branch of cephalopod evolution, hypothetically derived from bactrites, was represented by the subclass of belemnites (Belemnoidea). Belemnites appeared in the Triassic, flourished in the Cretaceous, and became extinct at the beginning of the Cenozoic era. In their appearance, they are already closer to the modern subclass Coleoidea. In body shape, they resemble modern squid (Fig. 246, B). However, belemnites differed significantly from them in the presence of a heavy shell, which was overgrown with a mantle. The shell of the belemnites was conical, multi-chambered, covered with leather. Remnants of shells and especially their terminal finger-like rostrum, which are figuratively called "devil's fingers", have been preserved in geological deposits. Belemnites were often very large: their length reached several meters. The extinction of ammonites and belemnites was probably associated with increased competition with bony fishes. And now, in the Cenozoic, a new group of cephalopods enters the arena of life - coleoids (subclass Coleoidea), devoid of shells, with fast reactive motion, with a complexly developed nervous system and sensory organs. It was they who became the "primates" of the sea and could compete on equal terms as predators with fish. This group of cephalopods appeared more
in the Cretaceous, but reached its highest flowering in the Cenozoic era. There is reason to believe that Coleoidea have common roots of origin with belemnites.
Ecological radiation of cephalopods... The ecological radiation of cephalopods is shown in Figure 247. From primitive shell benthopelagic forms, which are able to emerge due to the hydrostatic apparatus, several paths of ecological specialization were determined. The most ancient ecological trends were associated with the radiation of nautilids and ammonites, which swam at different depths and formed specialized shell forms of benthopelagic cephalopods. The transition from benthopelagic forms to bentonectonic forms (of the belemnite type) is traced. In them, the shell becomes internal, and its function as a swimming apparatus weakens. Instead, they develop the main mover - the funnel. They later gave rise to shellless forms. The latter undergo violent environmental radiation, forming nektobenthos, nekton, benthic and planktonic forms.
The main representatives of nekton are squids, but there are also fast-swimming octopuses and cuttlefish with a narrow torpedo-shaped body. The composition of nektobenthos mainly includes cuttlefish, often swimming
Rice. 247. Ecological radiation of cephalopods
or lying at the bottom, to Bentonekton - octopuses, which crawl more along the bottom than swim. Plankton include umbellate, or gelatinous, octopuses, rod-shaped squids.
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 fourgill molluscs have an external shell. The rest of the double-headed cephalopods, capable of rapid and prolonged movement, have only shell rudiments, 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 most quickly. At the rear end of their body there are fins - movement stabilizers. Benthic forms - octopuses - have a saccular 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 torso. The leg, characteristic of all mollusks, is greatly modified. The back of the leg has turned into a funnel, a conical tube leading into the mantle cavity. The funnel is located behind the head on the ventral side of the body. She is the organ with which mollusks swim. In the cephalopod mollusk of the genus Nautilus, which has retained many of the most ancient features of the structure of the cephalopods, the funnel is formed by folding a leaf-shaped leg with a common wide sole into a tube. In this case, the wrapped edges of the leg do not grow together. Nautilus, with the help of their feet, either slowly crawl along the bottom, or rise and slowly swim, carried by currents. In other cephalopods, the funnel lobes are initially separate, while in adult animals they grow together into a single tube.
Around the mouth are tentacles, or arms, which are seated with several rows of strong suction cups and have powerful muscles. It turns out that the tentacles of the cephalopods, like the funnel, are homologues of a part of the leg. In embryonic development, the tentacles are laid on the ventral side behind the mouth from the rudiment of the leg, but then move forward and surround the mouth opening. The tentacles and funnel are innervated from the pedal ganglion. The tentacles in most cephalopods are 8 (in octopods) or 10 (in decapods), in primitive mollusks from the genus Nautilus - up to 90. The tentacles are used to capture food and move; the latter is characteristic mainly of benthic octopods, which walk along the bottom on their legs. The suckers on the tentacles in many species are armed with chitinous hooks. In decapods (cuttlefish, squid), two out of ten tentacles are much longer than others and are seated at widened ends with suckers. These are trapping tentacles.
Mantle and mantle cavity
The mantle covers the entire body of the cephalopods; on the dorsal side, it grows together 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 gap located between the mantle and the body and extending 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 the cephalopods swim, and move forward with the rear 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 is pressed 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 is closed. In this case, water is forcefully pushed out of the mantle cavity through the funnel. The body of the animal is pushed back a certain distance. This is followed by relaxation of the mantle muscles, 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 impetus. Thus, rapidly following each other alternately contraction and extension of the muscles of the mantle enable the cephalopods to swim at high speed (squid). The same mechanism creates the circulation of water in the mantle cavity, which ensures respiration (gas exchange).
In the mantle cavity there are gills with the structure of typical ctenidia. Most cephalopods have one pair of ctenidia, and only the nautilus has two 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; the nautilus also contains osphradia in the mantle cavity.
Sink
Most modern cephalopods have no 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 genus of Nautilos is very ancient, very little changed since the Paleozoic. The nautilus shell is spirally twisted (in the plane of symmetry) over the head. Inside, it is divided by partitions into chambers, and the body of the animal is placed only in the front part, the largest chamber. A siphon process extends from the back of the nautilus body, which passes through all the septa to the apex of the shell. With this siphon, the shell chambers are filled with gas, which reduces the density of the animal.
Modern biplane cephalopods are characterized by an internal underdeveloped shell. The spiral shell is most fully preserved only in the small mollusk Spirula, which leads a benthic life. In cuttlefish, a wide and thick porous calcareous plate remains from the shell, lying on the dorsal side under the mantle. It has a supporting function. In squid, the shell is represented by a narrow dorsal chitinoid plate. Some octopuses have two conchiolin sticks under their mantle. Many cephalopods have completely lost their shell. Shell rudiments play the role of skeletal formations.
For the first time, an internal cartilaginous skeleton appears in cephalopods, which carries protective and supporting functions. In biparticles, a cartilaginous head capsule is developed, which surrounds the central nervous system and statocysts, as well as cartilage of the bases of the tentacles, fins, and cufflinks of the mantle. The tetragill 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 to the 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 that opens into a saccular stomach. In some species (for example, octopuses), the esophagus forms a lateral protrusion - goiter. The stomach has a large blind appendage, into which the ducts of the usually two-lobed liver open. A small (endodermic) intestine leaves the stomach, which makes a loop, heading forward, and passes into the rectum. The straight, or posterior, intestine opens with the anus, or powder, in the mantle cavity.
The duct of the ink sac flows into the rectum in front of the powder. This pear-shaped gland secretes an ink fluid that 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 hide from persecution.
Respiratory system
The gills, or ctenidia, of cephalopods are located symmetrically in the mantle cavity in the number of 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 musculature of the mantle.
Circulatory system
The heart of a cephalopod usually consists of a ventricle and two atria, only the nautilus has four. Two aortas branch off from the ventricle - the head and the 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 of the vessels into the vena cava, which form blind protrusions that protrude into the walls of the kidneys. Before entering the ctenidium, the bearing gill vessels (vena cava) form muscular dilatations, or venous hearts, which pulsate and facilitate the flow of blood into the gills. The 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, since 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 whole, containing the heart, stomach, part of the intestines and gonads, is found in primitive four-gill cephalopods. In decapods, the whole is more strongly reduced and is represented by two separate areas - pericardial and genital; in octopods, 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 their connection with the pericardium) and open with excretory holes 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 occurs. The pericardial glands also have an excretory function.
Nervous system
Biparticulate cephalopods are superior in height to the organization of the nervous system of all invertebrates. All ganglia characteristic of these mollusks converge and form the brain - a common nerve mass that surrounds the beginning of the esophagus. Individual ganglia can only be distinguished in sections. There is a division of paired pedal ganglia into tentacle ganglia and funnel ganglia. From the back of the brain are nerves that innervate the mantle and form two large stellate ganglia in its upper part. From the buccal ganglia, the sympathetic nerves that innervate the digestive system depart.
In primitive tetragill, the nervous system is simpler. It is represented by three nerve semicircles, or arcs, - the supraopharyngeal and two subpharyngeal. Nerve cells are distributed evenly on them, without forming ganglion clusters. The structure of the nervous system of tetragill is very similar to that of chitons.
Sense organs
In cephalopods, they are highly developed. Tactile cells are located throughout the body, especially they are concentrated on the tentacles.
The organs of smell of two-gill are special olfactory pits, and osphradia is present only in the Nautilus, i.e., in the four-gill.
All cephalopods have complex statocysts located in the cartilaginous capsule that surrounds 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 eyes of the Nautilus are most simply arranged. They represent a deep eye fossa, the bottom of which is formed by the retina.
The eyes of the bipillus cephalopods are much more complex. The eyes of a cuttlefish have a cornea, iris, lens, vitreous humor, and a highly developed retina. Attention is drawn to the following features of the structure of the eye of the cephalopods. 1. Many molluscs have a small opening in the cornea. 2. The iris also forms an opening - the pupil, leading to the anterior chamber of the eye. The pupil can contract and dilate. 3. A spherical lens formed by two fused halves is not able to change the 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 the lens of a photographic camera is set to focus. 4. The retina consists of a huge number of visual elements (for 1 mm 2 of the retina there are 105,000 visual cells in the cuttlefish, and 162,000 in the 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 of the ship 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 lobes of the leg. The shell is thin, almost transparent, and spirally twisted. It serves as a brood chamber in which eggs are hatched. The male of the boat is many times smaller than the female and does not have a shell.
The sex glands and reproductive ducts in most cephalopods are unpaired. Females are characterized by the presence of two or three paired and one unpaired nidamental glands, which secrete a substance from which the shell of eggs is formed. In males, spermatozoa are enclosed in spermatophores of various shapes.
The method of fertilization in cephalopods is of great interest. They do not really mate. In sexually mature males, one of the tentacles is greatly altered, it turns into a hectocotylized tentacle, or hectocotyl. With the help of such a tentacle, the male takes out spermatophores from his mantle cavity and transfers them to the female's mantle cavity. In some cephalopods, especially in the ship described above (Argonauta), the hectocotylized tentacle has a complex structure. After filling the tentacles with spermatophores, it breaks off and floats on its own, and then climbs into the mantle cavity of the female, where fertilization takes place. Instead of the detached hectocotyle, a new one is regenerated.
Large cephalopod eggs are laid in groups on various underwater objects (under stones, etc.). The eggs are covered with a dense shell and are very rich in yolk. The fragmentation is incomplete, discoidal. Direct development, without metamorphosis. A small, adult-like mollusk emerges from the egg.
Classification
The class of cephalopods (Cephalopoda) is divided into two subclasses: 1. Tetrabranchia; 2. Bilateral (Dibranchia).
Subclass Tetrabranchia
This subclass is characterized by the presence of four gills and a large outer shell, divided by septa into many chambers. The subclass is divided into two orders: 1. Nautiloidea; 2. Ammonites (Ammonoidea).
Nautilids in the 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, a non-accrete funnel of the leg, remnants of metamerism in the form of two pairs of gills, kidneys, atria, etc. The Nautilids survived little changed to our time since the Paleozoic. These living fossils are the remains of the once rich fauna of the fourgill cephalopods. Up to 2500 fossil nautilid species are known.
Ammonites are a completely extinct group of four-gill molluscs, which also had a spirally twisted shell. More than 5000 fossil ammonite species are known. Remains of their shells are common in Mesozoic sediments.
Subclass Dibranchia
The subclass of two-gill is characterized by an internal reduced shell (or its absence); their respiratory organs are represented by two gills. The subclass is divided into two groups: 1. Decapods (Decapoda); 2. Eight-legged (Octopoda).
Squad Decapods (Decapoda)
For decapods, the most characteristic is the presence of 10 tentacles, of which 2 are trapping ones; many of them retain a shell rudiment. Representatives - cuttlefish (Sepia officinalis), different kinds fast-swimming squids from the genus Ommatostrephes (hundreds of herring chasing shoals), from the genus Loligo, etc.
Decapods existed already in the Triassic, and they possessed an internal, more developed shell. Found often in the Mesozoic sediments with devil's fingers "represent the remnant of the back of the shell of the Mesozoic decapod belemnites (Belemnoidea) - pelagic animals resembling squid in shape.
Squad Eight-legged (Octopoda)
Unlike decapods, these are mainly benthic animals, with eight tentacles, devoid of shells. Representatives are different types of octopuses, as well as Argonauta, etc.
The most important representatives of the class of cephalopods and their practical significance
Modern cephalopods are an essential part of the marine and oceanic fauna. They are distributed mainly in the southern seas and seas with a fairly high salinity. In Russia, most of all cephalopods are in the Far Eastern seas. There are cephalopods in the Barents Sea. Cephalopods do not live in the Black and Baltic Seas due to the low salinity of these seas. Cephalopods are found at very different depths. There are many deep-sea forms among them. As predators, cephalopods feed on various marine animals: fish, crustaceans, molluscs, etc. Some of them cause great harm, destroying and spoiling schools of valuable commercial fish. Such are, for example, the Far Eastern squid Ommatostrephes sloani pacificus.
Among the cephalopods, there are very large forms, up to 3-4 m and more. The largest known cephalopod is the deep-sea squid (Architeuthis dux), which belongs to the decapod molluscs. This real giant among cephalopods, and indeed among invertebrates, reaches 18 m in length, with a tentacle length of 10 m and a diameter of each tentacle of 20 cm. found in the stomachs of killed 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 used for food by humans. So, cuttlefish and octopuses are eaten by the population of Mediterranean countries. In many countries, cuttlefish and squid are fished.
Cephalopods are the most unusual, largest and most highly organized of the molluscs. A number of unique features - great activity, method and speed of movement, unusually highly developed nervous system, rudiments of "intelligence", a set of means of defense and attack - puts cephalopods above all other groups of invertebrates and allows them to compete with vertebrates.
At first glance, cephalopods - octopuses, cuttlefish and squid - do not in any way resemble other molluscs. They (except Nautilus) there is not even a shell so typical for soft-bodied ones.
Rice. 22. Squid Wonderful lamp of Lycoteuthis diadema.
These mollusks got the name "cephalopods" because they have limbs on their heads - tentacles, with the help of which many animals can move along the bottom. In addition, it has been established that the limbs of the cephalopods developed from the legs of an ancient ancestor.
The sizes of cephalopods are very different. Among them there are dwarfs, the length of the mantle of which is less than 1 cm and giants, which include squids. Their body length, together with tentacles, can reach 18 m.
Cephalopods are exclusively marine animals. They play a very important role in ocean life. As predators, they eat a huge number of crustaceans, fish and, in turn, themselves serve as food for many marine vertebrates - fish, birds, pinnipeds and whales. The main enemy of cephalopods is the giant toothed whale - the sperm whale.
Cephalopods are bilaterally symmetrical animals.
In cuttlefish, the body is flattened, in squid it is cylindrical, pointed towards the posterior end, fusiform, in octopuses it is saccular. In all cephalopods, the body is clothed with a skin-muscular bag - a mantle that encloses the internal organs. On the sides of the mantle, squid, cuttlefish and pelagic octopus have fins of the most varied shapes and sizes, and serve as mollusks for swimming and as rudders. The head of most cephalopods is large, often somewhat wider than the mantle and separated from it by a cervical intercept, but in octopuses the head is spliced with the mantle. The head bears eyes, often, especially in deep-sea squids, very large, and tentacles surrounding the mouth of the mollusk with a crown.
The inner surface of the tentacles (arms) is seated with suction cups. They are located in 1 - 4 (rarely more) longitudinal rows.
A muscular conical tube adjoins the underside of the head, and sometimes grows, with its base extending into the mantle cavity. it funnel, or siphon, the main propeller of the cephalopod, its "jet engine".
The mouth of the cephalopods is small. The pharynx is muscular, equipped with two strong chitinous jaws, reminiscent of a parrot's beak and called " beak". In the oral cavity on a special lingual protrusion - odontophore a radula is placed - a chitinous ribbon, seated in rows of small denticles. With the help of the radula, food that has entered the mouth of the mollusk and moistened with saliva is transported further into the esophagus. A thin tube of the esophagus stretches from the pharynx to the stomach, piercing the brain and liver on the way to the stomach. Therefore, the cephalopods, in spite of their great appetite, cannot swallow the prey whole, but are forced to crush it into small pieces with their “beak” before sending it into the mouth. The pieces of food eaten then enter the gizzard, where the digestive juices produced by the liver and pancreas enter. The enzyme activity of these glands is very high, and food is digested in 4 hours. Absorption occurs in the blind appendix of the stomach - cecume as well as in the liver. Undigested food debris enters the intestine and is thrown out.
In the upper part of the mantle cavity there are gills- one on both sides of the internal mass.
The blood is set in motion three hearts – the main consisting of a ventricle and two atria, and two gill... The main heart drives blood through the body, and the rhythmic contractions of the gill hearts push venous blood through the gills, from where it enriched with oxygen enters the atrium of the main heart. The heart rate depends on the temperature of the water. For example, in an octopus at a water temperature of 22 ° C, the heart rate is 40-50 beats per minute.
In cephalopods, the circulatory system is almost closed: in many places (skin, muscles) there are capillaries through which the arteries pass into the veins.
The blood of cephalopods is blue due to the presence of respiratory pigment in it. hemocyanin, containing copper. Hemocyanin is produced in special gill glands.
A highly developed circulatory system makes it possible for cephalopods to reach gigantic proportions.
The organs of excretion are the renal sacs, the appendages of the gill hearts and the gills themselves. The main metabolic product of cephalopods is ammonia (more precisely, ammonium ions).
All cephalopods are dioecious. Male cephalopods are usually smaller than females, and when they mature, one or two of their arms will change, turning into hectocotyl, with the help of which males, during copulation, transfer spermatophores to the seminal receptacles of the female.
Spermatophores - "packets" with seminal fluid - are complex and have different types have different shapes. Usually the spermatophore is a thin, slightly curved tube, shaped like a Cossack saber. Spermatophores are formed in a special section associated with the testis - the spermatophores organ; they accumulate in a special storage - the spermatophore bag. During mating, the spermatophores go out through the excretory canal, are picked up by the hectocotyl and are transferred to the spermatozoa of the female. In cuttlefish and some squid, the seed receptacle is located on the female's oral membrane.
The nervous system in cephalopods is more complex than in other invertebrates. In terms of complexity, it is not inferior nervous system fish. The ganglia are very close together and essentially form a single nerve mass - the brain, which, in intra-cancerous cephalopods, is also enclosed in a cartilaginous capsule - the skull. In terms of relative mass, the brain of cephalopods is superior to that of fish, but inferior to the brain of birds and mammals.
The brain consists of lobes, the total number of which in an octopus is 64. The optical lobes are the largest of them - they can account for 4/5 of the brain volume. Cephalopods surpass many marine animals in subtlety of feelings, accuracy of perception and complexity of responses and behavior. Cephalopods are characterized by good memory, and they distinguish between short-term, intermediate and long-term memory. Octopuses and cuttlefish train well, and they solve some problems as well as rats.
Among the senses, the eyes have reached the greatest complexity and perfection. The eyes are usually placed in the recesses of the cartilaginous head capsule and have a cornea, an iris with a pupil capable of constricting and dilating, a lens and a retina. There is even an eyelid, as, for example, in the onychoteutid squid, which can close the eye.
The octopus's eye is almost indistinguishable from the eyes of mammals and humans. But there are still differences between them. For example, the cornea of the eye in most cephalopods is not solid, but is pierced in front by a small (in cuttlefish) or rather wide (in squid) aperture. The lens of the eye in cephalopods is not elliptical, but round, divided in half by a thin epithelial plate. Eye accommodation (setting vision at different distances, focusing) in cephalopods is achieved by removing or bringing it closer to the retina.
None of the inhabitants of the sea have such keen eyes as cephalopods. Only the eyes of an owl, a cat and a person can compete with them.
And cephalopods hold the record for eye size. The cuttlefish's eye is only ten times smaller than itself. The giant squid has eyes the size of a car headlight. In many deep-sea cephalopods, the eyes occupy most of the head.
The tactile and taste buds are located on the suction cups of the hands. Cephalopods recognize the taste of food mainly with their hands. The rims of the suction cups contain a huge number of taste-sensitive cells, so each sucker participates in the tasting of food.
Cephalopods also have organs of smell: in squid, these are papillae, or papillae, located on the head below the eyes, and in octopuses, these are olfactory pits.
In the occipital part of the cartilaginous skull of cephalopods, there are two statocysts - organs of balance. This is a pair of bubbles filled with liquid and containing limestone stones inside - statoliths. At the slightest change in the position of the body, statoliths touch sensitive cells, the walls of the vesicle, and the animal is oriented in space.
As for hearing, it is not yet clear whether cephalopods have it. It is believed that they are deaf, and it has even been suggested that deafness is a special device that protects these molluscs from the shock that can be caused by the sonars of whales - their worst enemies.
Cephalopods live only in oceans and salty seas. The salt content in water must be at least 33 0. therefore, these molluscs are not found either in the Black or Baltic Seas. They are extremely abundant in tropical and subtropical waters, but they also inhabit temperate waters and polar seas.
Cephalopods have long been eaten. In China, Japan and Korea, the use of these animals as food goes back centuries; in Mediterranean countries it also has a very long history. Ancient writers, in particular Aristotle, Plutarch and Pliny, report that in ancient Greece and ancient Rome, the skillfully cooked octopus was a common food. Cephalopods were also used in medicine and perfumery. Decorations were made from beautiful nautilus shells, paint and ink were made from sepia cuttlefish ink.
And until now, in the countries of the Mediterranean and Southeast Asia, cephalopods are very popular. They are prepared in ice cream, fresh, dried and canned.
Recently, interest in cephalopods has increased dramatically. It was caused by the unfavorable state of fish stocks and the need to find additional biological resources that are not yet used by fishing, which could compensate for the deficiency of protein food. Therefore, a whole complex of features puts cephalopods in the category of valuable game animals. In terms of the main indicators of nutritional value - calorie content and protein composition - squid and other cephalopods are superior to other mollusks and even some fish eaten and are only slightly inferior to beef and veal.
To this should also be added a high yield of production - 80% of the mass of the mollusk is used for food. Moreover, even the insides of cephalopods are valuable, since they contain a large number of various substances from which potent drugs can be prepared. Thus, cephalopods can be fully utilized, 100%.
Control questions:
What are the characteristic structural features of molluscs?
What classes is the Clams type divided into?
What are the main structural features of the class Gastropods?
What is the structure of bivalve molluscs?
What is the structure of mollusks of the class Cephalopods?
What is the significance of Molluscs in nature, human economic activity?
