What kind of animal makes squid. Breeding features of squid. Sea spray Images from the reefs of Papua New Guinea

Indeed, squid, unlike cuttlefish or octopuses, do not seek to charm the female, trying on catchy colors and protecting a convenient area of \u200b\u200bthe bottom from competitors, and not showing proudly prominent parts of their body, hinting at their readiness for a long act.

The main characteristics of the process, how squid breed, is speed and practicality, no sentimentality, just a short meeting for transfer necessary details mating is a spermatophore. Reproduction of squid takes place with the help of a special tube containing sperm, the length of which can vary from centimeter to meter. The spermatophore is a rather complex biological device, equipped with a powerful ejection apparatus, a sensitive hair, a complex membrane and a kind of "tube" that releases glue.

Initially, the spermatophore is located in the nidhem sac of the male and is transmitted to the female when they meet with the help of the penis or a modified hand, equipped with special clamps that ensure a firm grip. On the body of the female there is a place intended for the placement of a spermatophore, depending on the type of squid, this can be the mouth membrane, a fossa in the area under the beak or on the back of the head, the inner side of the mantle or the gill zone. Having got rid of the "load", the male leaves his girlfriend and does not participate in the breeding process anymore, sometimes it takes a long time from the moment the sperm tube is handed over to fertilization. It is possible that the fathers of the little squid have long been dead when they are born, since the male is quite unceremonious and can calmly transfer the spermatophore to the female, until she reaches puberty and is not capable of spawning.

As soon as the spermatophore is removed from the male and attached to the female's body, its membrane comes into contact with sea water, as a result of which the sensitive hair ruptures the thin membrane, provoking the so-called spermatophore reaction.

Water penetrates into the spermatophore and exerts pressure on the spring, due to which the inner shell of the cunning natural device also breaks. The spring literally flies out and pulls the inner part of the organ behind it, but at the same time the "tube" is triggered, releasing the glue that securely fixes the sperm bag on the female's skin.

It turns out that the sperm is ready for spawning and it remains to wait until the female decides to reproduce the offspring, which, by the way, happens only once in the life of a squid. If the female is sexually mature, she soon begins to lay eggs, which pass near the spermatophore attached to the gills. When the device is placed on the back of the head, sprinkling takes place through holes located on the sides of the neck, but fertilization is guaranteed in any case.

Thus, several dozen eggs are laid, which the female can hide in a secluded place, for example, among dense thickets of algae. However, spawning often occurs directly to the bottom, where there is an accumulation of squid, and many clutches of whitish and oblong eggs look like a huge carpet.

In most species, the larvae bear little resemblance to their parents immediately after birth, but within 2 months the small squids change outwardly and become sexually mature participants in the endless chain of spermatophore transmission.

By the way, there is still a secret in the reproduction of some species of cephalopods, for example, males have not been found in the species of hooked squid, however, fertilization with the help of a spermatophore occurs, and the apparatus is placed in a long cut on the abdomen, which the female cannot perform with her beak.

Deep-sea inhabitants of the depths of the sea are in no hurry to reveal their own secrets to a person, you can know how squid reproduce, but not imagine what makes this type of cephalopod literally produce offspring, not showing the slightest sympathy for each other.

The type of molluscs is divided into 7 classes: shellless, monoplacophores, carapaces, shovelpods, bivalves, gastropods, and cephalopods.

Shellless (Aplacophora) mollusks have a worm-like body up to 30 cm long, completely covered by a mantle, there is no shell. On the ventral side, they have a groove with a roller - a leg rudiment. There are no nephridia. This group of molluscs are hermaphrodites.

Breeding and breeding squid

The class has been known since the Cambrian. About 150 families and 20,000 species. Sea and freshwater bivalves feed on plankton and detritus by filtering water through siphons at the back of the shell. Some people drill into hard rocks and wood (using the sharp teeth of the shell or dissolving the rock with the acid released). The ship's worm damages the bottoms of ships and piers, cutting long passages through them. Some bivalve molluscs (oysters, mussels, scallops) are eaten. The sea squirt is one of my favorite sea creatures. Imagine my surprise when it splashes right in my eyes! The creature is well named, but there is more to this amazing animal than its "syringe pistol." Sea spray belongs to a wonderful group of underwater animals called shells. While it was hard to see from their soft bodies, the sea spray is also part of the Filam chordates - a group of animals that includes fish, birds, reptiles, and mammals! This is due to the fact that at their larval stage, sea spray has many anatomical features of vertebrates. The shells of gastropods (Gastropoda) are twisted into a spiral and differ in a wide variety of shapes. In some mollusks, the shell is submerged inside the body or is absent altogether. There is a pair of tentacles with eyes on the head. In the course of evolution, gastropods have lost their bilateral symmetry. In many species, the symmetrical organs located on the right side of the body have been reduced. Some species have a kind of lung - a cavity filled with air or water with oxygen dissolved in it. There are both hermaphrodites and dioecious forms. Marine syringes come in an amazing variety of shapes and colors. On the surface, they may look like sponges. Or they may look like rubber blobs when they live in colonies. Or they may even look like grapes. If you want to see some of the best images of marine syringes on the Internet, then you should stop at Madang - Ples Bilun Mi. This is a wonderful photo report by my friend Jan Messersmith. Sea spray Images from the reefs of Papua New Guinea The sea spray does have their brains After the ability to blow you in the eye, probably the most common syringes are "eat their brains." Which isn't nearly as violent as it sounds, but the life cycle of marine syringes is “extreme” and fun nonetheless. The larvae of the sea syringes begin to consume all the tadpole-like parts that made them chords. Where the gills of the sea syringe larvae once had, he develops a technique and contains siphons to help him bring water and food into his body. It absorbs its twitching tail. It consumes his primitive eye and his vertebral nasal sign. Finally, he even absorbs the rudimentary little "brain" that he used to swim and find his place of attachment. So, yes, in general, the sea syringe "eats its own brain" as it is. But since the sea syringe no longer needs a brain to help it swim or see, this is not a big loss for the creature. This requires the use of this now surplus material for the body to help develop its digestive, reproductive and circulatory organs. The remains of the shell sometimes remain under the skin in the form of a horny plate; the outer shell was found mainly in the extinct forms. The nautilus are the only modern cephalopods that still retain an outer spiral shell. The circulatory system is well developed; the blood has a blue color due to the hemocyanin, which is part of the erythrocytes. Cephalopods breathe with gills, some are able to stay on land for a long time (several hours or even days) thanks to the water stored in the mantle cavity. A marine syringe is basically a large stomach inside a bag. The bag also pumps water on its own, filtering food carried by the sea currents. Water enters one siphon and goes down into a large basket that resembles a throat. The pharynx has numerous lattice slots for the passage of incoming water. The plankton in the incoming water gets into the sticky mucus that covers the pharynx, and the small hairy cilia help move the plankton into the stomach for digestion. Filtered water and waste are removed through a second siphon. Sea spray are fascinating animals. They may look primitive, but they are actually one of the most advanced marine invertebrates. They start to look like tadpoles and end up looking like pretty leather bags and drops. In this process, they "lose their minds," so to speak! There is a funnel (siphon) at the entrance to the mantle cavity, which is the second part of the modified leg. Due to the reactive force arising from the water thrown out of it backward, the animal moves forward with the rear end of the body. Muscle contractions occur at a very high frequency, which ensures uniform movement. This is achieved, in particular, by the high conductivity of nerves - in some squid their thickness reaches 18 mm. A movement speed of 55 km / h was recorded in squid. Cephalopods can also swim, helping themselves with tentacles. Some squids, pushing water out of the siphon near the sea surface, can rise into the air for several meters. In the larval stage, the marine syringe has characteristics that make them part of the same chordate type to which all fish, birds, reptiles and mammals belong. In its adult form, the marine syringe is more than a water pump, pumping water into the vascular system, extracting nutrients, and pumping water out. Truly, the marine syringe has one of the most extreme and unusual life cycles of any animal. It is definitely one of the most unusual and strangely beautiful creatures in our oceans. It has a lot of great science, with a lot of discussion about how sea spray spreads. A brief introduction to the biology of cephalopods. The organs of vision are perfect. Human-like eyes have a lens and a retina; in giant squids, their size exceeds 40 cm. There are also miniature thermal locators on their fins. The sensitive organs of smell (or taste) are concentrated on the inner surface of the tentacles and on the suction cups. The developed organs correspond to the large brain. For passive protection from enemies, autotomy is used (cephalopods "throw away" the tentacles by which the enemy grabbed them) and ink curtains, which are possibly poisonous, are sprayed aside. In addition, special cells scattered over the skin - chromatophores and iridiocysts - allow changing the color of the body, "adjusting" to the environment. Some cephalopods are capable of luminescence. Cephalopods can grow to gigantic sizes - 18 m and more (their weight can reach several tons). There are numerous stories about giant octopuses (krakens), allegedly dragging sea vessels to the bottom. All cephalopods are dioecious. Male octopuses carry sperm into the female's mantle cavity with a special tentacle - hectocotyl. It often breaks away from the body and swims on its own in search of a female. The female usually incubates eggs, sometimes building nests. Cephalopods live in seas (up to a depth of 5 km), preferring warm water bodies. Some forms live among coastal rocks, others - at great depths. Some swim in the water column, others crawl along the bottom. Almost all of them are predators, feeding on fish, crustaceans, and other molluscs; prey is caught with tentacles, killing it with the secret of poisonous glands. Many cephalopods (squid, cuttlefish, octopus) are eaten by humans. The class is divided into two subclasses: four-gill (extinct ammonites and the only surviving genus of the Nautilus) and two-gill (cuttlefish, squid, octopus and extinct belemnites). About 600 modern species.

Biologist Henk-Jan Hoving of the University of Groningen is interested in how squid reproduces Decapodiform cephalopods... In addition to this cephalopod, Hoving investigated at least ten more species of squid and cuttlefish - from a 12-meter giant squid to a mini-squid no more than 25 mm long.

Deep sea squid is still very difficult to study because it is very difficult to get to, Hoving says. Observing these cephalopods in their natural environment requires a special technique. Therefore, the biologist had to reconstruct the sexual habits of squid, being content with already dead specimens and descriptions of other specialists. Still, the Dutchman managed to make some discoveries.

As the biologist himself says, "Reproduction is not fun, especially if you are a squid."

In the species of mollusks Taningia danae, males during mating injure the body of the females with beaks and hooks to a depth of five centimeters. And all because this type of squid simply does not have suckers. But partners derive considerable benefit from such "self-harm". In the cuts, males put "bags" containing spermatozoa - spermatophores.

The same method is used by representatives of another variety of deep-sea "multi-armed" - Moroteuthis ingens... True, the process of such a kind of fertilization in these squids is more peaceful. Spermatophores penetrate the skin without injuring it. According to Hoving, males have a substance, most likely an enzyme, that allows them to "melt" the skin.

Hoving found evidence that spermatophores penetrate the skin on their own. The biologist was able to see this process in freshly caught squid. Moreover, Japanese doctors have registered a case of squid spermatophores growing into human tissue. Not so long ago, in the Land of the Rising Sun, an operation was carried out, during which "sperm bags" of a cephalopod were removed from the throat of some sashimi lover.

Here comes the mini squid Heteroteuthis dispar decided to increase the birth rate. Females of this species fertilize their eggs on their own, inside the body. According to Hoving, they have formed a special bag for storing sperm, which is directly connected to the internal body cavity and reproductive organs.

When mating, males fill this container with sperm. Moreover, it is so generous that its stock can be up to 3% of the female's body weight. According to the biologist, this method has many benefits for both sexes. Females can grow eggs for a long time and fertilize them gradually as they mature. And the "bombed" males have a guarantee that their girlfriends will have very specific sperm.

Found Hoving among squid and "effeminate" males. Squids are not snails; they usually do not have hermaphroditism. But have Ancistrocheirus lesueurii discovered small glands that are involved in the production of eggs in females. The body length of these non-males was also not quite standard - more than that of normal "men".

Hoving cannot explain this phenomenon and believes that it is the result of exposure to hormones and hormone-like substances from human pills. Which first with waste water fall into the coastal zones of the ocean, and then to the depth. But, adds the biologist, it may turn out to be the squid's own "invention" - a kind of way to get closer to women.

The scientist hopes that his research will not only help to learn more about deep-sea cephalopods, but will also save them from human greed. Indeed, not only research probes penetrate to the depth, but also new fishing trawls.

Description

Spread

The species is common in the coastal waters of the eastern part of the North Atlantic from the North Sea to West Africa, as well as in the Mediterranean and Adriatic seas. It preserves at a depth of about 100 m and more, but it can also occur at a depth of 400 to 500 m.

Reproduction

In the north of the range in the North Sea, breeding begins in early spring after dark. Animals arrive there before the height of summer. The clutch consists of several elongated, sausage-shaped eggs, which attach to a fixed substrate at a depth of about 30 m.This can be parts of the seabed, for example, rock, as well as parts of a living creature, such as calcareous shells of other mollusks, dead organic material or the like. However, several animals prefer to lay their eggs in a common place. The larvae are morphologically similar to adult specimens, differing in the ratio of body parts to each other. Their size at the time of their appearance in June is less than 1 cm. The period of development of embryos until hatching at temperatures above 20 ° C is 20 to 30 days, at temperatures less than 15 ° C - approximately 40 to 50 days.

Value

Common squid, especially in the European Mediterranean countries, is an integral part of the diet and is therefore commercially caught. It is relatively easy to catch large flocks of animals in large numbers, so the catch is economically profitable.

Notes

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See what "Common squid" is in other dictionaries:

Squid Squid Mastigoteuthis flammea Scientific classification ... Wikipedia

- (Loligo) an animal from the class of cephalopods (Cephalopoda), the order of the bipod Dibranchiata), the suborder of decapods (Decapoda), from this. Myopsidae. The genus Loligo is characterized by an elongated, posteriorly pointed body, with a pair of triangular fins along ... Encyclopedia of Brockhaus and Efron

- (Loligo) an animal from the class of cephalopods (Cephalopoda), the order of two-legged (Dibranchiata), the suborder of decapods (Decapoda), from this. Myopsidae. The genus Loligo is characterized by an elongated, posteriorly pointed body with a pair of triangular fins ... ...

- (Loligo) an animal from the class of cephalopods (Cephalopoda), order of two-gill (Dibranchiata), suborder of decapods (Decapoda), from this. Myopsidae. The genus Loligo is characterized by an elongated, posteriorly pointed body with a pair of triangular fins ... ... encyclopedic Dictionary F. Brockhaus and I.A. Efron

In the external structure of squid, sexual dimorphism is relatively weak. If in some octopuses, in particular in Argonautidae, males are many times smaller than females, then in squid dwarf males or females are unknown.

Sexual differences in squid are most clearly expressed in the modification of one or several hands in males - hectocotilization. Usually, hectocotilization begins much earlier than males become sexually mature. In most cases, one of the abdominal arms, more often the left, is hectocotilized. The distal part of the hand always changes.

In some species, the hectocotilized area occupies only an insignificant part of the total arm length, in others it begins almost from its very base. The length of the hectocotyl is subject to age and individual changes. The variability of the size of the hectocotyl is evidenced, for example, by the following data: in Doryteuthis singhalensis, the hectocotl is 50-58% of the arm length, in Uroteuthis bartschi - 39-45%, in Loligo duvauceli - 54-61%, in L. edulis - 69-71% , in Sepioteuthis lessoniana - 24-33%, etc.

In many squids (Onychoteuthidae, Gonatidae, Octopodoteuthidae, etc.), apparently, there is no hectocotilization at all.

The biological meaning of the hectocotyl lies in the fact that it is used to transfer spermatophores from the mantle cavity of the male to the mantle cavity or to the seminal receptacle on the oral membrane of the female, but how the role of the hectocotyl in the act of copulation is carried out is not entirely clear.

In sexually mature females and males, there are some differences in body proportions. Usually in females, the mantle is somewhat thicker, which is associated with the strong development of the ovary and indigenous glands. By the time of spawning, the absolute weight of the female gonads is several times higher than the weight of the male gonads in males of the same size. The ovary is greatly enlarged and often occupies more than half of the volume of the mantle cavity. As a result, the rear end of the mantle thickens, becomes more massive and blunt. A. Verril, during a thorough morphological study of squid Loligo pealei, first discovered that in females the suckers on the tentacles and arms are larger, the head is more massive, the fins are shorter, but wider than in males. Further studies showed that morphological differences between males and females are characteristic of all squid species, only the degree of these differences is not the same for different species. For example, Loligo duvauceli females, in comparison with males, are characterized by a wider mantle, shorter and narrower fins, shorter arms, and smaller suckers.

Oegopsida females are usually larger than males, while in Myopsida, on the contrary, males are often larger than females.

Sex ratio

Data on the sex ratio in cephalopods are scarce and contradictory. This is due to the limited amount of material usually in the hands of researchers, since the collection of squid at sea in most cases is carried out sporadically. As a result, we can talk about the sex ratio not in the entire population, but only in some part of it. For example, in the coastal regions of the Mediterranean Sea in January and February, males of Loligo vulgaris are more numerous than females, in March, the number of males and females is equalized, and then females prevail. This is due to the fact that males of this species mature earlier than females and come to the shores earlier for spawning. Unequal sex ratios in catches can also be explained by different sizes males and females. The males of Alloteuthis media are smaller than the females and therefore more easily pass through the mesh of the trawls.

Analyzing the available data obtained by various authors, we are inclined to believe that the true sex ratio in squid is close to 1: 1, and any significant deviations from this proportion are caused by errors in the collection of materials. However, for example, in Todarodes sagittatus, females predominate in the population, the number of which is several, sometimes many times greater than the number of males. The predominance of females is typical for Dosidicus gigas, Symplectoteuthis oualaniensis, and possibly Lolliguncula mercatoris.

Mating and fertilization

Mating in squid occurs mainly in two ways.

The first way - partners come closer and take a head-to-head position. Their hands are intertwined. With a hectocotilized hand, the male takes out spermatophores from his mantle cavity and transfers them to the seminal receptacle on the female's oral membrane.

Second way - the male does it under the belly of the female or approaches from the side so that his head is at the level of her mantle. The male clasps the female's mantle with its limbs and holds it tightly, and then with the hectocotilized hand transfers the spermatophores into the female's mantle cavity.

Judging by the fact that spermatophores sometimes attach to the nape of the female, are embedded in the tissue of the outer surface of the mantle, are placed in the back of the mantle cavity, etc., there are other copulation methods, but they have not been directly observed by anyone.

One species of squid copulates only in the head-to-head manner, filling the seminal receptacle on the female's oral membrane with sperm (Loligo vulgaris, Todor odes pacificus, Dosidlcus gtgas, Symplectoteuihis oualaniensis, apparently also U. sagit talus, Todaropsis t eblattae e. ), others transfer spermatophores only to the mantle cavity of the female, for example, Illex illecebrosus. However, some squid species copulate in both the first and second ways (Loligo pealei, L. opalescens, Sepioteuthis lessoniana t Doryteuthis plei). Apparently, the combination of different mating methods provides more reliable fertilization of eggs.

The behavior of squid during the mating period is interesting. Both males and females are unusually excited. Females of Loligo pealei continuously move in short jerks, making intricate movements with their hands, then folding them together, then spreading them apart. The males ready to mate follow the females all the time, keeping up with them. Then the male makes a jerk and grabs the female in front by the head. They are intertwined by hands and remain in this position throughout the entire period of copulation. The male captures the bundles of spermatophores emerging from the mantle cavity through the funnel, and with the help of the hectocotyl transfers them to the female's oral membrane, where it holds for some time until all the sperm comes out and fills the seminal receptacle. The whole operation takes about 10 seconds. In this way, L. pealei usually copulates some time before spawning, when the eggs of the females are not yet ripe. Squids are mated again before laying eggs. The male holds the female with his hands by the mantle and at the same time, capturing the spermatophores emerging from the funnel with the hectocotyl, transfers them into the female's mantle cavity. Part of the sperm is immediately carried back by the current of water, but most of it remains near the oviduct. Mating is repeated several times. Individual males are sometimes so excited that they try to mate with other males and deposit spermatophores in their mantle cavity.

Fertilization of eggs in squid occurs in the mantle cavity, when the eggs leave the genital opening, or when they pass along the cone of the arms - at this time, sperm flows out of the buccal seminal receptacle and fertilizes the eggs.

Size and number of spermatophores

Formed spermatophores accumulate in a special spermatophores sac (nidhem organ of the male). Filled with cum they white... The process of spermatophores formation in mature males goes on continuously, so that the nidhem organ always contains a certain supply of them.

Externally, the spermatophore of squid looks like a tube sealed at one end or, more precisely, a test tube closed with a cork. The spermatophore consists of a reservoir with sperm and a rather complex ejection (ejaculatory) apparatus. The main part of this apparatus is a coiled elastic thread, a spring that stretches from the head of the spermatophore to the sperm reservoir, where it is attached to a special cementing body. The spring retains the sperm until the spermatophore "explodes". When the spermatophore is on the oral membrane or in the mantle cavity of the female, the sticky secretion of the cementing body attaches the bubble with sperm ejected from the shell of the "exploded" spermatophore to the surface of the female's body.

The length of spermatophores in cephalopods is very different. The longest spermatophores in the octopus Outopus dofleirti (1.2 m). In some octopuses, the length of the spermatophores is equal to the length of the mantle and even exceeds it.

The absolute sizes of spermatophores in squid vary from 2 mm (Enoploteuthidae) to 10-20 cm in giant squid of the genus Architeutkis.

The relative sizes of spermatophores in squid are small compared to octopuses, they do not exceed 20-25% of the mantle length. Squids of the family Loliginidae have relatively small spermatophores; their maximum length does not exceed 7-8% of the mantle length. Very large relative sizes of spermatophores in the family Ommastrephidae - 16-25% of the mantle length.

The size of the spermatophores increases with the growth of the animal, but more slowly than the size of the body. For example, in Loligo vulgaris from the Mediterranean Sea, with a mantle length of 14 cm, the length of spermatophores is 7% of the length of the mantle, and with a mantle length of 30 cm - 6%.

The sizes of spermatophores are not the same in representatives of the same species from different geographical areas. The one-sized males of Octopus vulgaris from the Mediterranean have longer spermatophores than those from the Western Atlantic.

Apparently, there is a definite relationship between the size of spermatophores and their number. In Loliginidae, spermatophores are small, but numerous: in Loligo vulgaris, 800 or more, in L. pealei, up to 400. In Ommastrephidae, which have larger spermatophores, their number is 100-250, and only in such large species as Dosidicus gigas - 300-1200. Apparently, the smaller the relative size of the spermatophores, the greater the number. The same dependence is characteristic of cuttlefish and octopuses: Sepia officinalis, which has short spermatophores (relative length - 7.6-5.9%) - about 1400; in Pteroctopus tetracirrhus (relative length 91.1-100.0%) - only 12 pieces.

The number of spermatophores in the nidhem organ increases with age; two-year-old males have more spermatophores than yearlings.

Number and size of eggs

The eggs of cephalopods are usually oval, evenly elongated along the long axis, less often pear-shaped or spherical.

Most octopuses and cuttlefish have very large eggs, for example, the octopus Octopus conispadiceus has an egg diameter of 30 mm. In squid, they usually do not exceed 2.5-3 mm, and only representatives of the genus Sepioteuthis have large eggs (up to 1.5 cm in diameter).

Naturally, the smaller the eggs, the greater their number develops in the female's ovary, so that the fertility of squid and the size of their eggs are inversely related.

The size of mature eggs practically does not increase with the growth of females, as a result of which large females are more fertile than small ones that mature for the first time.

The process of maturation of eggs in the ovaries varies from species to species. In a few squids, for example, in some Cranchiidae, eggs do not ripen all at once, but in separate small groups throughout the life of the female. Eggs are spawned as they ripen and spawning is in portions.

In most squid, by the time of spawning, almost all the eggs contained in the ovary mature, so that spawning occurs at the same time. In Loligo vulgaris, for example, almost all eggs in the ovary are spat.

Despite the one-time spawning, in the ovaries of females during the pre-spawning period there are 3-4 groups of eggs, differing in color and size. Small, immature eggs are usually opaque; as they mature, they accumulate yolk, grow in size, become transparent and turn yellow (Loligo vulgaris), yellow-orange (Lolliguncula brevis) or orange color (Illex illecebrosus coindeti).

Fertility of squid varies from several dozen (Sepioteuthis) to several hundred thousand eggs (Ommastrephes caroli, Dosidicus gigas, Symplectoteuthis oualaniensis). Probably, pelagic squids inhabiting the open parts of the seas and oceans are more fertile than coastal species. For example, neritic Loliginidae usually lay no more than 3-5 thousand eggs, and oceanic species Ommastrcphidae and Cranchiidae - tens and hundreds of thousands.

Egg laying

Squid clutches are of two types - bottom and pelagic. Each egg in the clutch is dressed with a dense elastic shell, and on top of the entire mass of eggs is enclosed in a gelatinous capsule or shapeless mass. The outer shells of the eggs are secreted by the oviductal and nondamental glands, so that the eggs are laid already protected by the shells.

The size and shape of the clutches can serve as a specific feature. The clutches of squid Loligo vulgaris, L. forbesi, pealei, L. opalescens, Alloteuthis media, A. subulafa, Sepioteuthis lessoniana, S. sepioidea and other coastal species are well known.

Clutches of all Myopsida are benthic: They look like thick gelatinous cords or pods of various lengths attached by the base to the substrate - rocks, shells, rock fragments, corals, sea grass, algae or simply to the bottom. Females use their hands to gently attach the egg-filled capsules, weaving their stems together.

Usually, the female lays mature eggs in one place in the form of a single clutch, however, some squids make several clutches. For example, in Alloteuthis media, the female lays no more than 200-300 eggs in one place (out of a total of 1000-1400), so that the clutch of one female is scattered on the bottom in several places.

In contrast, in Loligo vulgaris, the female tries to lay her eggs where there are already clutches of other females of the same species. This leads to the fact that in places the laid eggs of L. vulgaris thickly cover the bottom over a considerable area. In L. opalescens, eggs are also laid in large piles, often occupying areas of the bottom up to 12 m in diameter.

Bottom clutches of Loliginidae are located near the coast, in the upper sublittoral. Often, in stormy weather, a mass of eggs and corpses of spawned squid is thrown ashore in waves.

Sepioteuthis lessoniana spawns in southern India in shallow areas of bays and bays overgrown with seagrass and algae, which often dry up in the dry season. The eggs of this squid attach not only to bottom objects and grass, but also to the remains of floating vegetation - branches, tree trunks, etc.

Representatives of each species prefer very specific soils and depths. In the Gulf of Lyon, females of Loligo vulgaris spawn mainly on sandy and silty soils at depths of 20-80 m, while Alloteuthis media prefers silty soils or thickets of Posidonia seagrass at depths of 10-30 m.

Some Ommastrephidae also lay eggs at the bottom. These are Todarodes pacificus, apparently also T. sagittatus, Illex illecebrosus, etc.

Very little is known about the behavior of male and female squid after oviposition. It was found that females of Loligo opalescens keep close to clutches during their development. Doryteuthis plei females guard the clutch for some time and wash it with fresh water. However, most squids die shortly after spawning, so the clutch develops without parental control, unlike octopuses from the family Octopodidae, whose females literally "incubate" eggs, constantly stay near them, periodically pouring fresh water from the funnel and driving away numerous predators. As a rule, the female octopus does not feed during the entire period of egg development and dies after the larvae hatch. Female Argonauts carry their eggs in special shells on their backs.

It can be assumed that most oceanic squids have pelagic eggs. This assumption is supported by the fact that many species of squid constantly live away from the coast above great depths, inhabiting the water column and not migrating to coastal waters.

Pelagic clutches of squid known to researchers are of the same type in their structure. They look like a wide (up to 30 cm) and long (up to 1-2 m and more) transparent pink or whitish gelatinous tape, muff or sausage, inside which eggs lie in more or less regular rows. Each egg is separated from the neighboring by significant gaps. Clutch 1.5-1.8 m long and 30 cm wide contains about 20 thousand eggs. Such masonry has a very delicate consistency and is torn into pieces, often in the shape of a ball, under the influence of winds, waves and currents. Ribbon-shaped or spherical clutches of squid are most often found in the surface layers of water. During the period of egg development (before the larvae hatch), pieces of such clutches seem to have time to disperse over a large area.

The wide dispersal of squid is also facilitated by the fact that they often spawn in jets of ocean currents. This is evidenced by the accumulation of early larval stages of squid in the currents. Thus, K. Hu discovered a large number of Cranchiidae larvae and the Guinean Current. We found concentrations of squid larvae near the Bab el-Mandeb Strait. With distance from it to the north and to the south, as the current weakened, the number of larvae sharply decreases.

Spawning period

Data on the spawning time can be obtained both by direct observation of clutches in the sea, and indirectly - by studying the degree of maturity of the gonads, as well as by detecting early larval stages of squid in plankton. The first method is, of course, the most reliable. Unfortunately, direct observations of squid clutches in the sea are very limited (coastal species Loligintdae).

For many squid, the spawning season is established only by comparing indirect data.

The spawning time of different species, even within the same basin, is different. Some prefer the spring months, others summer, and others late summer and autumn. However, most often squid spawn in the warm season. This is especially pronounced in the boreal region, where the seasonal dynamics of water temperature reaches the highest values. True, the main spawning of Todarodes pacificus occurs in winter - in December-January, but for spawning this squid migrates to the extreme south of its range, to the subtropical waters of southern Japan.

In the direction of the subtropical and tropical regions, the spawning periods of squid are becoming more and more extended. This applies both to species that live only in these areas and to widespread species. The relatively deep-sea species also have a very extended spawning period.

Loligo vulgaris spawns in North Morse for three months a year - from early May to July. In the Mediterranean, however, it reproduces for almost a year round - from January to October - November. The same can be said about Alloteuthls media - in the North Sea, this species spawns only at the height of summer - in June-July, while in the Mediterranean it spawns all year round... Spawning of Todarodes pacificus in Japanese waters lasts almost all year, but this species has two spawning groups - winter, breeding only in the extreme south of Japan, and summer, breeding both in the north and in the south of the country. The limitation of the spawning season for cephalopods in relatively high latitudes largely depends on climatic conditions and, above all, on water temperature.

Already in the Mediterranean Sea, most cephalopod species spawn for 8-10 months, and often all year round. The same can be said for the squid of the Florida and California coasts.

If spawning occurs year-round, this does not mean that its intensity remains unchanged throughout the year. Usually there is a season of more active breeding - peak spawning. For example, in the Florida Lolliguncula brevis it occurs in September - October, in the Mediterranean Loligo vulgaris in June, in the California L. opalescens in May-June, in the Argentine Illex illecebrosus in December-March.

In the Red Sea and Indian Ocean, mature female squid Loligo edulis. L. duvauceli, Seploteuthis lessoniana, Symplectoteuthis oualaniensis occurred in autumn, winter, and spring (no observations were made in summer). Females of S. oualaniensis with mature transparent yellow eggs were caught in the Gulf of Aden in November and January. In addition, in January, in the center of the Gulf of Aden above a depth of about 1000 m, a pelagic spherical clutch of Ommastrephidae was caught in the surface layer, which, in our opinion, belongs to S. oualaniensis.

Females of Loligo edulis, L. duvauceli, Doryteuthis sibogae with mature eggs were regularly caught in our trawls in the shelf waters of South and East Arabia and along the coast of West Pakistan in February-May at depths of 20-120 m (no deeper trawling).

In ichthyoplankton collections carried out in the Red Sea and the Gulf of Aden in the fall of 1963 (October-November), many squid larvae of the families Loliginldae, Ommastrephidae, Enoploteuthidae and Chiroteuthidae were found in the early stages of development. Their length did not exceed 2-5 mm. Apparently, the spawning of most squid species in this area is year-round.

It is believed that spawning of Cephalopoda depends not only on water temperature, but also on the length of daylight hours. Thus, in the Mediterranean Sea, where the water temperature does not have any significant limiting effect on spawning, in species with a short spawning period it falls mainly in June-July, i.e., during the period of the longest days of the year. In the winter months, squid spawning usually dies out or stops altogether.

Key questions

In what cases are mollusks useful or harmful to humans?

What other groups of animals are mollusks close to?

What are the main groups of mollusks and what are their fundamental differences?

Mollusca species inhabit a variety of habitats, from the ocean depths to the treetops of tropical rainforests. Described about 80,000 existing species of molluscs, which are divided into six main classes. The most primitive mollusks, chitons, belong to the class Amphineura; the class Mo-noplacophora was considered extinct until its living representatives were found; the class Gastropoda includes snails, slugs and saucers; the Pelecypoda class includes bivalves - molluscs and oysters; the class Scaphopoda includes shoveling molluscs. Representatives of the class Cephalopoda - squid and octopus - are considered by many to be the most highly organized of all invertebrates (Fig. 14-1).

The garden snail, it would seem, has little in common with the giant squid or oyster, nevertheless, the body structure of all Mollusca groups is similar. All molluscs have a leg, which is a muscular structure that allows movement ( component the Latin name of some classes of molluscs - poda - means "leg"). The snail moves smoothly with the help of its leg, the mollusk, pushing its leg between the shell valves, is buried in sand or silt. Squids and octopuses differ from other types of molluscs in that their limbs have evolved into tentacles, which they use for locomotion and other purposes.

Molluscs have mantle - the tissue that covers most of the body and forms a shell. A shell-like formation is the internal structure of the skeleton and is a thin stratum corneum... Inside mantle cavities water-dwelling molluscs have gills, terrestrial ones have primitive lungs.

Molluscs have a digestive system with mouth and anus.

With the exception of bivalves, the mouth of all molluscs is equipped with a grater ( radula), with which they grind particles of food, shell or wood.

The circulatory and nervous systems in different classes of molluscs vary from the simplest to the most complex.

Most of these animals are dioecious organisms, and some are hermaphrodite. There are species that are males at first, and become females in the later stages of life. Like annelids, molluscs often go through the larval stage of trochophora (Figure 13-4), but, unlike annelids, their adults are not segmented.

14.1. Gastropoda is the most representative and most diverse class of molluscs

The variety and beauty of the shells of this class of molluscs contributed to their wide collection, study and classification. Therefore, at present, more is known about the evolutionary development of gastropods than about any other groups of invertebrates. Gastropods, snails and related forms are the most freely roaming molluscs and are equally widespread in seas, freshwater basins and on land. Many of them have a single-leaf, spirally twisted and brightly colored shell. On land, snails are usually found in areas with lush vegetation. Some of them are eaten, in particular in France - garden snails Escordot, in Japan - gastropods Buccinum.

14.2. Common garden snails - typical gastropods

In snails, there are three main body parts: the area that includes the head and leg, internal organs, the complex of the mantle and shells.

The structures that make up the first area perform the functions of the senses, movement and ingestion of food. These organisms do not have a clear boundary between head and leg. For example, in the garden snail Helix, the head and leg are part of the body that moves out of the shell as the animal moves (Figure 14-2). The "sole" of the leg is covered with cilia and glides over the surface due to the coordinated movements of these cilia. Mucus, which is secreted by large glands located under the mouth opening, serves as a lubricant during the sliding movement of the cochlea, especially on a dry surface. The sticky properties of the mucus allow the snail to crawl vertically and even upside down. The snail has negative geotropism, which lies in the fact that, being placed on a table or branch, the oya crawls up. This reaction apparently helps the snail to quickly get to the leaves of the plants it feeds on. On the outer part of the snail's head there are two pairs of palps (at the ends of the longer pair there are eyes), the organs of balance - statocysts - and the mouth opening. AT oral cavity the radula is located, which is a hard jagged chitinous strip that covers the hard tongue. The muscles attached to the two ends of that jagged strip move back and forth like a file and grind food. The inwardly directed teeth facilitate the movement of food into the esophagus. As they wear out, new teeth form at the posterior end of the radula. Subtle differences in the structure of the radula make it possible to classify closely related groups of molluscs.

The internal organs of the snail are represented by the circulatory system, digestion and excretory system. Helix are hermaphroditic organisms. Cross fertilization in them occurs by transferring sperm into the partner's vagina. Eggs covered with a gelatinous shell are laid by snails in humid places. At hatching, the offspring are tiny snails.

Helix has a single kidney that drains the area around the heart, filtering waste from body fluids that is removed through a nearby duct. The snail has a so-called open circulatory system. The heart pumps blood through closed vessels to various parts of the body. Blood then flows freely through the open sinuses into the tissue and is eventually filtered back to the heart.

The most vulnerable internal organs are constantly inside the shell and protected by it. The muscles that connect the viscera to the apex of the shell can pull the entire body of the snail inward if needed.

Of course, the most conspicuous part of the mantle complex is the shell. It is a solid structure, but it dissolves quite easily in strong acids. The shell material is calcium carbonate crystals enclosed in a cellular protein structure. The hardness of the shell depends on the relative amount of calcium carbonate and protein released by the mantle. Under the shell of a snail, like all other mollusks, there is a mantle - a rather thin fold of tissue.

The edges of the mantle highlight new calcareous material that is deposited on the free edge of the existing shell.

The shell protects the mollusc from predators and also prevents the drying of terrestrial molluscs and species living in the marine littoral. During the dry season, the shell is tightly closed and the body of the mollusk is not exposed to air. In some snails, after the body is pulled inside, the neck of the shell is closed with a lime lid. Other types of snails secrete mucus that covers the exposed part of the shell. In laboratories and museums, snails are sometimes kept in dry vessels for five years or more, and even then they regain activity when placed in a humid environment. The presence of a shell and "lungs" in some gastropods allowed them to become the single most adapted group of terrestrial mollusks.

Garden snails belong to the order of molluscs called Pulmonata (from the Latin word pulmonis for lungs) and can breathe air. The gills, present in the mantle cavity in most mollusks, have been replaced in Pulmonata by an area of \u200b\u200bthe mantle tissue that is saturated with blood vessels. The loops of these vessels are connected to small cavities. The air entering the cavity then penetrates into the blood through a specialized surface of the mantle. The development of such a respiratory system is an example of adaptation to terrestrial existence.

14.3. The molluscs Mercenaria mercenaria, which have various names (vein c, hard shell), are representatives of bivalve molluscs

Mercenaria mercenaria is widespread, for example, on the east coast of the United States. These molluscs are small in size, 5 to 7 cm across, and range in color from white to bluish gray. Small individuals are called a hard shell, larger ones are called a venus. Like most bivalves, Mercenaria is a marine species, although many other mollusk species can thrive in fresh water.

The nature of the body contractions of these mollusks (Fig. 14-3) differs significantly from gastropods. Clam Mercenaria resembles a laterally compressed gastropod, which has no head.

The body of the mollusk is located between two shell valves fastened from the dorsal side. When the adductor muscles contract, the shell valves close tightly and can remain in this position for a long time (After these muscles relax, the valves open due to the elastic properties of the shell lock.

In Mercenaria, only the leg and siphons can protrude beyond the shell, through which water flows to the gills.

Because most molluscs live in bottom sand or silt, they lack a brain-like structure with its many sensitive and neural structures that are needed to receive information from the environment.

A mantle is located on the inner surface of the shell, which is clearly visible at the edge. In molluscs, this tissue secretes shell material and forms two siphons, which circulate water through the cavity of the mantle, which contains the gills and leg. Part of the mantle can form a brood chamber in which juveniles develop in some bivalves, although Mercenaria does not have such a structure.

The mollusk can quickly remove the leg, siphons and other soft parts of the body into the shell, but it pushes them again much more slowly. This is because these parts of the body are retracted inward as a result of contraction of the trailing muscles, and are released again as the pressure of the fluid in the siphons and the leg is equalized.

The pelecypod mollusk is buried with a foot in wet sand or silt.

The Ensis mollusk (sea stalk) and related species break up the sand much faster than a person can do even with a shovel. First, the clam plunges the thin end of the leg into the silt, which then fills with blood and unfolds to form a mushroom-like anchor (Figure 14-4). With the contraction of the muscles of the body, the shell is pulled up to the end of the leg that is fixed in the silt and thereby sinks into the depth of the bottom. Then the leg is embedded even deeper into the bottom, and the cycle repeats.

14.4. With the exception of land snails, all molluscs have gills.

The gills of molluscs differ significantly in structure and function in different species. In Mercenaria, the gills consist of two pairs of loosely hanging folds located on either side of the leg in the mantle cavity. The dorsal ends of the gills are connected to the body of the mollusk, the ventral ends hang freely. The gills are composed of W-shaped inner and outer records (leaflets). Between the two plates is free spacedivided vertically into a row of narrow, water-filled tubes. Countless cilia vibrating on the surface of the gills direct water towards them, pumping it through one siphon and throwing it out through another. As water passes through the gills, oxygen and carbon dioxide are exchanged.

The gills also function as food “gatherers”. The water passing through the gills contains small organisms and organic particles. The mucous membrane constantly forming on the surface of the gills, as a result of the movement of particles, moves ventrally and collects food. The food, surrounded by mucus, enters a small, ciliated food channel, through which it is delivered to the mouth and swallowed. Thus, it can be seen that mollusks have adapted to a semi-sedentary mode of existence, in which all the necessary substances are delivered from the environment. Mercenaria can move within a limited area, although, undoubtedly, the mollusk spends most of its life in one place, buried in silt.

Mercenaria are dioecious organisms. The formation of gametes in these molluscs begins at the age of two in spring and summer, as soon as the water becomes warm enough. Male and female gametes are released simultaneously and, after passing through a siphon, are released into the sea, where fertilization takes place.

14.5. For humans, bivalve molluscs serve as one of the food sources, and, for example, the "shipworm" mollusk is only a source of trouble

Like other marine molluscs, fertilized eggs Mercenaria develop into a mobile larva - trochophore or veliger... These ciliated larvae are near the surface of the water and often drift long distances from their parents' habitat, which contributes to the spread of this species;

After a certain period of time, they undergo metamorphosis and become adults.

Molluscs and related forms are used by humans as a food source. Even in antiquity, shellfish and squid were eaten, and today, despite environmental pollution and devastating catch, which restrain the size of the catch, reliable estimates show that about 3 million tons of edible shellfish are caught in the world per year. In the USA, for example, about 55 thousand tons of oysters alone are caught annually. Molluscs are used to obtain dyes, as an additive in poultry feed, in road construction, for making buttons and decorations.

The bivalve molluscs Torado (tree worm) cause significant harm to humans by destroying wood. They sieve the underwater parts of rafts, docks and ships, causing billions of dollars in damage annually.

14.6. The Loligo squid is one of the most common cephalopods, or cephalopods.

All molluscs cephalopods are inhabitants of the seas. Many of them, such as squid and nautilus, live at great depths. The octopus prefers hollows and caves in relatively shallow areas of the sea.

The sizes of cephalopods range from microscopic squids found in plankton to giants up to 20 m long and up to 2 tons in weight. Researchers believe that there were also larger specimens that were not only the largest of all known invertebrates, but perhaps and the largest animals in general.

The Loligo squid (Fig. 14-5) has an elongated body. It does not have an external shell, and a thin internal horny core performs the function of a skeleton.

The squid's leg has transformed into 10 processes equipped with suction cups, of which two are tentacles. In the head region there are two well-developed eyes, which have many similarities to the eyes of vertebrates in structure, function and location (Fig. 14-5). The mouth is located at the base of the tentacles and is equipped with a horny beak and radula. The saliva secreted in the mouth is poisonous and apparently serves to immobilize the prey. The beak is very hard, with it the squid can break the shells of crabs and tear off pieces of fish.

The squid mantle is a cone-shaped structure that completely covers the internal organs. The fins on the sides of the body are formed from the fabric of the mantle. They provide swimming and stabilize body position in the water. A small tubular siphon, like tentacles, is a modified part of the leg. It protrudes from under the edge of the mantle and is used by squid for movement. It happens in the following way. Water enters the cavity of the mantle through its open neck or collar. Then the collar closes, the muscles of the mantle contract sharply and a stream of water is thrown out through the siphon, pushing the squid far away. By turning the siphon in different directions, the squid can quickly move in any direction. Apparently, he uses this method of movement only in special cases, usually swimming with the help of fins.

When irritated, squid and octopuses can release a black liquid from a special gland located in the cavity of the mantle. This cloud of ink will disorient their potential enemies and may be poisonous.

In addition, squid and octopus avoid encounters with predators, merging with the background of the environment. There are cells in the skin of these animals - chromatophores, capable of changing the location of the pigment, which changes the color of the integument of the animal. This allows them to acquire different color shades. Under some conditions, animals turn pink, in others - pale gray. Such a system not only provides a protective coloration, but is also used during the mating season and during defensive actions.

Courtship and mating in squid (and in octopuses) are very complex behavioral acts. The male has one specially modified tentacle, with the help of which he transfers sperm lumps from his mantle to the female's mantle. Fertilization takes place inside the female's body and subsequently a mass of eggs is released outside through her siphon. The female captures them with tentacles and molds from them long cords, "fingers of the dead", which she attaches to stones. Such a sequence of actions for a female is always the same and cannot be different. It will carry out the entire normal process of sculpting and then attaching a mass of eggs, even if they were experimentally removed immediately after exiting the siphon. This type of instinctive behavior is observed in many insects, birds and mammals. Once the behavioral process has begun, these animals cannot stop or change it. They must complete this process completely, even if it has become useless.

The cephalopods have a well-developed nervous system... Octopuses are able to distinguish between visual and tactile stimuli, they can even be trained to respond in a certain way to different stimuli. It is surprising that the eyes of squid and humans are very similar (Fig. 14-5).

Loligo has a giant nerve axon (nerve branch) that runs from the brain to the muscles of the mantle. And much of what we know today about the transmission mechanism nerve impulse, was found in experiments carried out on this nerve process. This axon was discovered in 1930, and soon researchers, inserting electrodes into nerve cellswere able to study electrical changes during nerve impulse conduction.

14.7. The presence of similar traits that are observed in annelids, molluscs and arthropods suggests that they all descended from related organisms

Despite the insufficient amount of data to establish a common ancestor of annelids, molluscs and arthropods, all three groups of animals have a large number of similar characteristics.

In particular, polychaetes and mollusks form a larva, a trochophora, and the embryonic development of their coelom is almost the same. However, the body of molluscs is never segmented. It was believed that the Neopilina mollusk (Fig. 14-6) belonged to a class that became extinct 400 million years ago, but when in 1952. these animals were discovered by an expedition of Danish scientists, it turned out that primitive mollusks are segmented. Numerous living specimens of these small molluscs were fished at 2 km depth in the north of the Gulf of Panama. Each of them has one shell, under which there are five pairs of external gills and eight pairs of muscles that attach the animal to the shell. However, it is now believed that this segmentation was acquired later and was not characteristic of primitive mollusks.

The relationship between annelids and arthropods is striking. First, arthropods are segmented, although this is not as pronounced as in annelids. Second, they have a nervous system similar to annelids with a ventral trunk that extends from the dorsal brain, or ganglion. In addition, the development of the coelom in these two groups proceeds in parallel ways. Further evidence of the link between the two is the existence of a small type of tropical worm-like organisms, Onychopora. Like annelids, these "walking worms" have a soft, segmented body with repetitive muscle and nephridia groups. Like arthropods, they have a dense chitinous cuticle, tracheal respiratory system, and paired "walking" limbs ending in claws. The limbs of Onychopora do not have joints, as in arthropods, but, like spiders and centipedes, movement of their limbs is carried out as a result of the interaction of flexor muscles (for raising the limbs) and hydraulic pressure (for extension, since there are no extensor muscles). The oldest Onychopora lived about 500 million years ago, in the Cambrian period, when arthropods evolved rapidly due to competition with annelids.