What animal makes squid. Features of reproduction of squids. Sea spray Images from the reefs of Papua New Guinea
Indeed, squids, unlike cuttlefish or octopuses, do not seek to charm the female, trying on catchy colors and guarding a convenient bottom area from competitors, and not proudly showing prominent parts of their bodies, hinting at a readiness for a long act.
The main characteristic of the process, how squid breed, speed and practicality, no sentimentality, only a short meeting to transfer required part mating - spermatophore. Squid reproduction occurs with the help of a special tube containing sperm, the length of which can vary from a centimeter to a 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 male’s needhem sac and is transferred to the female upon meeting with the help of a penis or a modified hand equipped with special clamps that provide a strong grip. On the body of the female there is a place intended for placing the spermatophore, depending on the type of squid, this can be the oral membrane, a hole 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 “burden”, the male leaves the girlfriend and no longer participates in the process of reproduction, sometimes a long period passes from the moment of delivery of the tube with spermatozoa to fertilization. It is possible that the daddy of little squids has long been dead when they are born, since the male is quite unceremonious and can easily transfer the spermatophore to the female, who has not yet reached puberty and is not capable of spawning.
As soon as the spermatophore is removed from the male and attached to the body of the female, its shell comes into contact with sea water, as a result of which the sensitive hair breaks the thin membrane, provoking the so-called spermatophoric reaction.
Water penetrates inside the spermatophore and exerts pressure on the spring, due to which the inner shell of the cunning natural device is also torn. The spring literally flies out and pulls out the inside of the organ, but at the same time the “tube” is triggered, releasing the glue that securely fixes the sperm sac on the skin of the female.
It turns out that the sperm is ready for spawning and it remains to wait until the female decides to reproduce offspring, which, by the way, happens only once in the life of squids. If the female is a sexually mature individual, she soon begins to throw eggs that pass near the spermatophore attached in the gill zone. When the device is placed on the back of the head, the balayage occurs through the holes located on the sides of the neck, but in any case, fertilization is guaranteed.
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 takes place right on 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, small squids change appearance and become sexually mature participants in the endless chain of spermatophore transmission.
By the way, there is still a mystery in the reproduction of some species of cephalopods, for example, no males were found in the species of hook-bearing squids, however, fertilization with the help of a spermatophore occurs, and the apparatus is placed in a long incision on the abdomen, which the female cannot perform with her beak.
Deep-sea inhabitants of the deep sea are in no hurry to reveal their own secrets to humans, you can know how squid reproduce, but not imagine what makes this type of cephalopod literally produce offspring, without showing the slightest sympathy for each other.
The type of molluscs is divided into 7 classes: shellless, monoplacophores, armored, spadefoot, 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 rudiment of the leg. 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. Marine and freshwater bivalves feed on plankton and detritus by filtering water through siphons at the back of their shells. Some drill through hard rock and wood (using sharp shell teeth or by dissolving the rock with acid). The shipworm damages the bottoms of ships and piers by cutting long passages into them. Some bivalves (oysters, mussels, scallops) are eaten. The sea squirt is one of my favorite sea creatures. Imagine my surprise when he splashes me right in the eyes! The creature is well named, but there's more to this amazing animal than its "syringe gun." Sea spray belongs to a remarkable group of underwater animals called shells. Although it was hard to tell by looking at their soft bodies, sea spray is also part of the chordate phylum - a group of animals that includes fish, birds, reptiles and mammals! This is because, in their larval stage, sea squirts have many vertebrate anatomical features. The shells of gastropods (Gastropoda) mollusks are twisted into a spiral and are distinguished by a wide variety of shapes. In some mollusks, the shell is immersed inside the body or is absent altogether. The head has a pair of tentacles with eyes. 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 were 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 marine syringe images on the internet, then you should stop by Madang - Bilun Mi Ples. This is a wonderful photo essay by my friend Jan Messersmith. Sea spray Images from the reefs of Papua New GuineaSea spray really has their brainsAfter the ability to blow you in the eye, probably the most common syringes are "eat their brains". What happens is not as much as it seems, but the life cycle of marine syringes is "extreme" and fascinating nonetheless.Sea squirt larvae begin to consume all the tadpole-like parts that made them chords. Where sea squirt larvae once had gills, it develops a habit and contains siphons to help it bring water and food into its body. It absorbs its twitching tail. He absorbs his primitive eye and his vertebral nasal sign. Finally, he even absorbs the vestigial little "brain" he used to swim and find his attachment spot. So, yes, in general, the sea syringe “eats its own brain”, such as it is. But since the sea syringe no longer needs a brain to help it swim or see, it's not a big loss for the creature. This is to use this now redundant body material to help develop its digestive, reproductive, and circulatory organs. The remains of the shell are sometimes preserved under the skin in the form of a horny plate; the outer shell was mainly in extinct forms. The only modern cephalopods that still retain an outer spiral shell are nautiluses. The circulatory system is well developed; The blood is blue in color due to hemocyanin, which is part of the erythrocytes. Cephalopods breathe with gills, some are capable of a long stay on land (several hours or even days) thanks to the water stored in the mantle cavity. A sea squirt is basically a large stomach inside a bag. The bag pumps water on its own, filtering the food carried by the sea currents. Water enters one siphon and descends into a large basket resembling a pharynx. The pharynx has numerous lattice slits for the passage of incoming water. The plankton in the incoming water gets caught in the sticky mucus lining the throat, 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 squirts are fascinating animals. They may look primitive, but they are actually one of the most advanced marine invertebrates. They start out looking like tadpoles and end up looking like beautiful leather bags and drops. In the process, they "lose their minds" so to speak! At the entrance to the mantle cavity there is a funnel (siphon), which is the second part of the modified leg. Due to the reactive force arising from the water ejected from it backwards, the animal moves forward with the rear end of the body. Muscle contractions occur at a very high frequency, which ensures uniformity of movement. This is achieved, in particular, by the high conductivity of the nerves - in some squids, their thickness reaches 18 mm. Squids have been recorded moving at 55 km/h. Cephalopods can also swim using their tentacles to help themselves. Some squids, pushing water out of the siphon near the sea surface, can rise several meters into the air. In the larval stage, the sea squirt has characteristics that make them part of the same chordate type to which all fish, birds, reptiles and mammals belong. In its adult form, a sea squirt is more than a water pump, pumping water into the vascular system, extracting nutrients, and pumping out water. Truly, the sea syringe has one of the most extreme and unusual life cycles any animal. It is certainly one of the most unusual and oddly beautiful creatures in our oceans. There's a lot of great science in it, with a lot of discussion about how sea spray spreads. 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 thermolocators on the fins. On inner surface tentacles and suckers are concentrated sensitive organs of smell (or taste). Developed organs correspond to a large brain. For passive protection from enemies, autotomy is used (cephalopods “throw away” the tentacles by which they are grabbed by the enemy) and ink curtains, possibly poisonous, are sprayed to the side. In addition, special cells scattered over the skin - chromatophores and iridiocysts - allow you to change the color of the body, "adjusting" to the environment. Some cephalopods are capable of luminescence. Cephalopods can grow to gigantic sizes - 18 m or more (their mass can reach several tons). There are numerous stories about giant octopuses (krakens), supposedly dragging ships to the bottom. All cephalopods are dioecious. Male octopuses transfer sperm into the mantle cavity of the female with a special tentacle - hectocotylus. Often it breaks away from the body and swims independently in search of a female. The female usually incubates the eggs, sometimes building nests. Cephalopods live in the seas (up to a depth of 5 km), preferring warm water bodies. Some forms live among the coastal rocks, others - at great depths. Some swim in the water column, others crawl along the bottom. Almost all 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 nautilus genus) and two-gill (cuttlefish, squid, octopus and extinct belemnites). About 600 modern species. |
Biologist Henk-Jan Hoving from the University of Groningen is interested in how squid reproduce Decapodiform cephalopods. In addition to this cephalopod, Hoving studied 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.
As Hoving says, studying deep-sea squid is still very difficult, because it is very difficult to get to them. To observe these cephalopods in their natural environment requires a special technique. Therefore, the biologist had to reconstruct the sexual habits of squids, content with already dead specimens and descriptions of other specialists. But 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 mollusk species Taningia danae, males, during mating, injure the body of females with their beaks and hooks to a depth of five centimeters. And all because this type of squid simply does not have suckers. But from such "self-mutilation" partners derive considerable benefit. In 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 peculiar fertilization in these squids is more peaceful. Spermatophores penetrate the skin without damaging it. According to Hoving, the males have some kind of substance, most likely an enzyme, that allows you to "melt" the skin.
Hoving found evidence that spermatophores penetrate the skin on their own. The biologist managed 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 performed, during which “sperm bags” of a cephalopod were removed from the throat of some sashimi lover.
And here is the mini squid Heteroteuthis dispar decided to raise the birth rate. Females of this species fertilize their eggs on their own, inside the body. According to Hoving, they developed a special pouch for storing sperm, which is directly connected to the internal cavity of the body and reproductive organs.
When mating, males fill this container with sperm. And so generously that its stock can be up to 3% of the body weight of the female. According to the biologist, this method has a lot of advantages for both sexes. Females can grow eggs for a long time and gradually fertilize them as they mature. And the “bombed out” males still have a guarantee that their girlfriends will have completely specific spermatozoa.
Found Hoving among squids and "effeminate" males. Squids are not snails, they usually do not have hermaphroditism. But Ancistrocheirus lesueurii found small glands that are involved in the production of eggs in females. The body length of these non-males also turned out to be 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 are first with sewage fall into the coastal zones of the ocean, and then to the depths. But, the biologist adds, it may also 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. After all, not only research probes penetrate into the depths, but also new fishing trawls.
Description
Spreading
The species is distributed in the coastal waters of the eastern North Atlantic from the North Sea to West Africa, as well as in the Mediterranean and Adriatic Seas. Keeps at a depth of about 100 m or more, but can also be found at a depth of 400 to 500 m.
reproduction
In the north of its 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 oblong, sausage-shaped eggs, which are attached to an immovable substrate at a depth of about 30 m. These can be parts of the seabed, such as rock, as well as parts of a living creature, such as calcareous shells of other mollusks, dead organic material or the like. At the same time, several animals prefer to lay their eggs in a common place. Larvae are morphologically similar to adult specimens, differing in the ratio of body parts to each other. Their size during the appearance in June is less than 1 cm. The period of development of embryos until hatching at a temperature of more than 20 ° C is from 20 to 30 days, at a temperature of less than 15 ° C - from about 40 to 50 days.
Meaning
The common squid, especially in the European Mediterranean countries, is an integral part of the diet and is therefore commercially harvested. It is relatively easy to catch large flocks of animals in large numbers, so the catch is economically viable.
Notes
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See what the "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 two-gill Dibranchiata), the suborder of the decapods (Decapoda), from the family. 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 the two-gills (Dibranchiata), the suborder of the decapods (Decapoda), from the fam. 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), the order of the two-branched (Dibranchiata), the suborder of the decapods (Decapoda), from the family. 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 squids, sexual dimorphism is relatively weakly expressed. 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 squids are most clearly expressed in the modification of one or more hands in males - hectocotylization. Usually hectocotylization begins much earlier than males become sexually mature. In most cases, one of the abdominal arms, more often the left, is hectocotylized. The distal part of the arm always changes.
The hectocotylized area in some species occupies only an insignificant part of the total length of the arm, in others it begins almost from its very base. The length of the hectocotyl is subject to age and individual changes. For example, the following data testify to the variability in the size of the hectocotyl: in Doryteuthis singhalensis, the hectocotyl 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.), hectocotylation apparently does not exist at all.
The biological meaning of the hectocotyl lies in the fact that with its help the transfer of spermatophores from the mantle cavity of the male to the mantle cavity or to the seminal receptacle on the oral membrane of the female is carried out, however, how the role of the hectocotyl is carried out in the act of copulation remains not entirely clear.
In sexually mature females and males, some differences in body proportions are observed. Usually in females, the mantle is somewhat thicker, which is associated with a strong development of the ovary and indamental glands. By the time of spawning, the absolute weight of the female gonads is several times greater than the weight of the male gonads in males of the same size. The ovary greatly enlarges and often occupies more than half of the volume of the mantle cavity. The posterior end of the mantle thickens as a result, becomes more massive and blunt. A. Verrill, during a thorough morphological study of the Loligo pealei squid, first discovered that in females the suckers on the tentacles and arms are larger, the head is more massive, and 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 in different types is not the same. For example, female Loligo duvauceli compared to males are characterized by a wider mantle, shorter and narrower fins, shorter arms, and smaller suckers.
Females of Oegopsida 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 explained by the limited amount of material that is 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 evens out, and then females predominate. This is explained by the fact that males of this species mature earlier than females and come to the shores for spawning earlier. The unequal sex ratio in catches can also be explained by different sizes males and females. The males of Alloteuthis media are smaller than the females and, therefore, pass through the trawl mesh more easily.
Analyzing the available data obtained by different authors, we tend to believe that the true sex ratio in squids 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, the population is significantly dominated by females, 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.
First way- Partners approach each other and take a head-to-head position. Their hands are intertwined. With a hectocotylized hand, the male takes the 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 his limbs and holds it tightly, and then transfers the spermatophores into the female's mantle cavity with his hectocotylized hand.
Judging by the fact that spermatophores are sometimes attached to the back of the female's head, drilled into the tissues of the outer surface of the mantle, placed in the back of the mantle cavity, etc., there are other methods of copulation, but they have not been directly observed by anyone.
One species of squid copulates only in a head-to-head manner, filling the seminal receptacle on the female oral membrane with sperm (Loligo vulgaris, Todor odes pacificus, Dosidlcus gtgas, Symplectoteuihis oualaniensis, apparently also U. sagit talus, Todaropsis eblattae u t.d. ), others carry spermatophores only into the mantle cavity of the female, such as Illex illecebrosus. However, some squid species copulate in both the first and second ways (Loligo pealei, L. opalescens, Sepioteuthis lessoniana t Doryteuthis plei). Apparently a combination different ways mating ensures more reliable fertilization of eggs.
The behavior of squids during the mating period is interesting. Both males and females are unusually excited. Loligo pealei females continuously move in short jerks, making intricate movements with their hands, then folding them together, then spreading them apart. Males ready for mating follow the females all the time, keeping up with them. Then the male makes a jerk and grabs the female from the front by the head. They intertwine with their hands and remain in this position during the entire period of copulation. The male captures bundles of spermatophores emerging from the mantle cavity through the funnel and, using the hectocotylus, transfers them to the female's oral membrane, where he holds them 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 copulate some time before spawning, when the eggs of the females are not yet mature. Before laying eggs, squids mate again. The male holds the female by the mantle with his hands and at the same time, grabbing the spermatophores emerging from the funnel with the hectocotylus, transfers them to the female's mantle cavity. Part of the sperm is immediately carried back by the flow of water, but the main part 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 emerge from the genital opening, or when they pass along the cone of the arms - at this time, the sperm flows out of the buccal seminal receptacle and fertilizes the eggs.
Size and number of spermatophores
The formed spermatophores accumulate in a special spermatophore sac (needham organ of the male). They are full of cum white color. The process of formation of spermatophores in mature males is continuous, so that the needhem organ always contains some reserve.
Outwardly, the squid spermatophore looks like a tube sealed at one end, or, more precisely, like 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 an elastic thread coiled in a spiral, 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 holds the sperm until the spermatophore "explodes". When the spermatophore is on the oral membrane or in the mantle cavity of the female, the sticky secret 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 are 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 squids vary from 2 mm (Enoploteuthidae) to 10–20 cm in giant squids of the genus Architeutkis.
The relative sizes of spermatophores in squids are small compared to octopuses, they do not exceed 20-25% of the mantle length. Squids of the Loliginidae family have relatively small spermatophores; their greatest 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 mantle length, 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. Single-sized Octopus vulgaris males from the Mediterranean have longer spermatophores than those from the Western Atlantic.
Apparently, there is a certain relationship between the size of spermatophores and their number. Loliginidae have small but numerous spermatophores: Loligo vulgaris has 800 or more spermatophores, and L. pealei has up to 400 spermatophores. In Ommastrephidae, which have larger spermatophores, their number is 100-250 pieces, and only in such large species as Dosidicus gigas - 300-1200. Apparently, the smaller the relative size of the spermatophores, the greater the number. Cuttlefish and octopuses are characterized by the same dependence: in Sepia officinalis, which has short spermatophores (relative length - 7.6-5.9%) - about 1400 pieces; in Pteroctopus tetracirrhus (relative length 91.1-100.0%) - only 12 pieces.
The number of spermatophores in the needhem 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, in the octopus Octopus conispadiceus, the egg diameter reaches 30 mm. In squids, 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 ovary of the female, so that the fertility of squids 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 prolific than small ones that mature for the first time.
The process of maturation of eggs in the ovaries is not the same in different species. In a few squids, for example, in some Cranchiidae, eggs do not mature all at once, but in separate small groups throughout the life of the female. Eggs are laid as they mature and spawning is portioned.
In most squids, by the time of spawning, almost all the eggs contained in the ovary ripen, so that spawning occurs at a time. In Loligo vulgaris, for example, almost all the eggs present in the ovary are swept out.
Despite the one-time spawning, in the ovaries of females in the pre-spawning period there are 3-4 groups of eggs that differ in color and size. Small immature eggs are usually opaque, as they mature they accumulate yolk, increase in size, become transparent and turn yellow (Loligo vulgaris), yellow-orange (Lolliguncula brevis) or Orange color(Illex illecebrosus coindeti).
The fertility of squid varies from a few 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 prolific 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.
oviposition
There are two types of squid clutches - bottom and pelagic. Each egg in the clutch is dressed in a dense elastic shell, and on top of the whole mass of eggs is enclosed in a gelatinous capsule or shapeless mass. The outer shells of the eggs are secreted by the oviduct and nidamental 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.
The clutches of all Myopsida are bottom-dwelling: They have the form of thick gelatinous cords or pods of various lengths, attached at the base to the substrate - stones, shells, rock fragments, corals, sea grass, algae, or simply to the bottom. Females use their hands to gently attach the egg-filled capsules by weaving their stalks 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.
On the contrary, 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 locally laid eggs of L. vulgaris cover the bottom in a thick layer over a large area. In L. opalescens, eggs are also laid in large heaps, often occupying areas of the bottom up to 12 m in diameter.
The bottom clutches of Loliginidae are located near the coast, in the upper sublittoral zone. Often, in stormy weather, a mass of eggs and corpses of spawned squids are thrown ashore by waves.
Sepioteuthis lessoniana in South India spawns in shallow, seagrass and kelp areas of bays and bays that often dry out during the dry season. The eggs of this squid are attached not only to bottom objects and grass, but also to the remains of floating vegetation - branches, tree trunks, etc.
Representatives of each species prefer well-defined soils and depths. In the Gulf of Lion, females of Loligo vulgaris spawn mainly on sandy and silty bottoms at depths of 20-80 m, while Alloteuthis media prefers silty bottoms or posidonia seagrass beds at depths of 10-30 m.
Some Ommastrephidae also lay their eggs on the bottom. These are Todarodes pacificus, apparently also T. sagittatus, Illex illecebrosus and others.
Very little is known about the behavior of male and female squids after oviposition. It has been established that females of Loligo opalescens stay close to the clutches during their development. Females of Doryteuthis plei guard the clutch for some time and wash it with fresh water. However, most squids die shortly after spawning, so that the clutch develops without parental control, unlike octopuses from the Octopodidae family, whose females literally “hatch” eggs, are inseparably near them, periodically watering them with fresh water from a 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 hatching the larvae. 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 squid species constantly live far from the coast over great depths, inhabiting the water column and not migrating to coastal waters.
Pelagic clutches of squids, 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 or more) transparent pink or whitish gelatinous ribbon, muff or sausage, inside which eggs lie in more or less regular rows. Each egg is separated from the next by significant gaps. The clutch, 1.5-1.8 m long and 30 cm wide, contains about 20 thousand eggs. Such masonry has a very delicate texture and, under the influence of winds, waves and currents, are torn into pieces, often shaped like a ball. Ribbon-like or spherical clutches of squids are most often found in the surface layers of water. During the period of egg development (before hatching of the larvae), pieces of such clutches apparently have time to disperse over a large area of water.
The widespread distribution of squids is also facilitated by the fact that they often spawn in the jets of ocean currents. This is evidenced by the accumulation of early larval stages of squids in the jets of currents. So, K. Hu discovered a large number of larvae of Cranchiidae and the Guinean Current. We found concentrations of squid larvae near Bab el Mandeb. With distance from it to the north and south, as the current weakens, the number of larvae decreases sharply.
spawning period
Data on 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 of Loligintdae).
For many squids, the spawning season has been established only by comparing indirect data.
The timing of spawning of different species, even within the same basin, is different. Some prefer the spring months, others - summer, others - the end of summer and autumn. However, most often squids spawn in the warm season. This is especially pronounced in the boreal region, where the seasonal dynamics of water temperature reaches highest values. True, the main spawning of Todarodes pacificus takes place in winter - in December-January, but for spawning this squid migrates to the extreme south of its range, to the subtropical waters of South Japan.
In the direction of the subtropical and tropical regions, the timing of squid spawning becomes more and more extended. This applies both to species living only in these areas, and to widespread species. Relatively deep water species also have a very extended spawning period.
Loligo vulgaris in the North Sea spawns for three months a year - from early May to July. In the Mediterranean Sea, it breeds almost all year round - from January to October - November. The same can be said about Alloteuthls media - in the North Sea, spawning of this species is observed only at the height of summer - in June-July, while in the Mediterranean Sea it spawns. all year round. Spawning Todarodes pacificus in Japanese waters lasts almost the entire year, but this species has two spawning groups - winter, breeding only in the extreme south of Japan, and summer, breeding in both the north and south of the country. The limitation of the spawning season of cephalopods at relatively high latitudes largely depends on climatic conditions and above all on the temperature of the water.
Already in the Mediterranean Sea, spawning of most cephalopod species lasts 8-10 months, and often all year round. The same can be said about the squid off the coasts of Florida and California.
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 reproduction - spawning peak. For example, in the Florida Lolliguncula brevis it occurs in September - October, in the Mediterranean Loligo vulgaris - in June, in the Californian L. opalescens - in May-June, in the Argentinean Illex illecebrosus - in December-March.
In the Red Sea and the Indian Ocean mature female Loligo edulis squid. L. duvauceli, Seploteuthis lessoniana, Symplectoteuthis oualaniensis occurred in autumn, winter, and spring (no observations were made in summer). Female 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 in the surface layer, a pelagic spherical clutch of Ommastrephidae was caught, which, in our opinion, belongs to S. oalaniensis.
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 (we did not trawl deeper).
In ichthyoplankton collections carried out in the Red Sea and the Gulf of Aden in the autumn of 1963 (October-November), many squid larvae from the families Loliginldae, Ommastrephidae, Enoploteuthidae, and Chiroteuthidae, which are at early stages of development, were found. Their length did not exceed 2-5 mm. Apparently, the spawning of most squid species in this area is year-round.
There is an opinion that the spawning of Cephalopoda depends not only on the temperature of the water, but also on the length of the daylight hours. Thus, in the Mediterranean Sea, where water temperature does not have any significant limiting effect on spawning, in species with a short spawning period, it occurs mainly in June-July, i.e., during the period of the longest days of the year. IN winter months squid spawning, as a rule, fades or stops altogether.
Key questions
In what cases are mollusks useful or harmful to humans?
What other groups of animals are close to mollusks?
What are the main groups of mollusks and what are their fundamental differences?
Members of the Mollusca phylum occupy a variety of habitats, from the depths of the ocean to the treetops of tropical rainforests. Described about 80,000 existing species mollusks, which are divided into six main classes. The most primitive mollusks - chitons - belong to the class Amphineura; the class Monoplacophora was considered extinct until its living representatives were discovered; the class Gastropoda includes snails, slugs and limpets; the class Pelecypoda includes bivalves - clams and oysters; the class Scaphopoda includes spadefoot molluscs. Representatives of the Cephalopoda class - squids and octopuses - are considered by many to be the most highly organized among 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 groups of the Mollusca type is similar. All mollusks have a leg, which is a muscular structure that provides locomotion ( component The Latin name for some classes of mollusks - poda - means "leg"). The snail moves smoothly with the help of its foot, the mollusk, pushing its foot between the shell valves, buries itself in sand or silt. Squids and octopuses are different from other types of molluscs because their limbs have evolved into tentacles that they use for locomotion and other purposes.
Shellfish have mantle- a tissue that covers most of the body and forms a shell. A formation similar to a shell is an internal structure of the skeleton and is a thin horn plate. Inside mantle cavity mollusks living in the water have gills, while terrestrial molluscs have primitive lungs there.
Mollusks have a digestive system with mouth and anus.
With the exception of bivalves, the mouth opening of all mollusks is equipped with a grater ( radula), with which they crush 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 hermaphroditic. There are species that are male at first and become female later in life. Like annelids, mollusks often go through the trochophore larval stage (Fig. 13-4), but, unlike annelids, their adults are not segmented.
14.1. The gastropoda Gastropoda is the most representative and most diverse class of molluscs.
The diversity and beauty of the shells of this class of mollusks contributed to their extensive 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 mollusks and are equally widespread in the seas, in 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. Ordinary garden snails - typical gastropods
In snails, three main body parts are distinguished: the area including the head and leg, internal organs, mantle and shell complex.
The structures that make up the first area perform the functions of the sense organs, 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 protrudes from the shell when the animal moves (Fig. 14-2). The "sole" of the foot is covered with cilia and glides over the surface due to the coordinated movements of these cilia. The mucus that is secreted by the large glands located under the mouth opening serves as a lubricant during the sliding movement of the snail, 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 means that when placed on a table or a branch, the oya creeps up. This reaction apparently helps the snail get to the leaves of the plants it feeds on quickly. On the outer part of the head of the cochlea there are two pairs of palps (the eyes are located at the ends of the longer pair), the organs of balance - statocysts - and the mouth opening. IN oral cavity a radula is located, which is a hard, serrated chitinous strip that covers the hard tongue. Muscles attached to the two ends of that serrated strip move back and forth like a file and grind food. The inwardly directed teeth help move food into the esophagus. As it wears, new teeth form at the posterior end of the radula. Subtle differences in the structure of the radula make it possible to classify close groups of mollusks.
The internal organs of the cochlea are represented by the circulatory system, digestion and excretory system. Helix are hermaphroditic organisms. Cross fertilization occurs by transferring sperm into the partner's vagina. Eggs covered with a gelatinous shell, snails lay in wet places. When hatched, the offspring are tiny snails.
Helix has a single kidney that drains the area around the heart, filtering waste from body fluids that are expelled 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. The blood then flows freely through the open sinuses into the tissues 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 insides to the top of the shell can, if necessary, draw the entire body of the snail inward.
Of course, the most prominent 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 snail shell, like all other mollusks, there is a mantle - a rather thin fold of tissue.
The edges of the mantle exude new calcareous material that is deposited on the free edge of the existing shell.
The shell protects the mollusk from predators, and also prevents terrestrial mollusks and species living in the sea littoral from drying out. During the dry period, the shell closes tightly and the body of the mollusk is not exposed to air. In some snails, after the body is drawn inward, the neck of the shell is closed with a calcareous cover. Other types of snails secrete mucus that covers the exposed part of the shell. In laboratories and museums, snails are sometimes kept in dry containers for five years or more, and even after that, they regain activity when placed in a humid environment. The presence of a shell and "lungs" in some gastropods has allowed them to become the single most adapted group of terrestrial molluscs.
Garden snails belong to the order of mollusks called Pulmonata (from the Latin word pulmonis - lungs) and can breathe air. The gills present in the mantle cavity of most molluscs are replaced by a patch of mantle tissue that is saturated with blood vessels in Pulmonata. 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 titles(vein with, hard shell), - representatives of bivalve mollusks
Mercenaria mercenaria are widely distributed, for example, on the East Coast of the United States. These shellfish small size, in diameter from 5 to 7 cm, their color varies from white to bluish-gray. Small individuals are called a hard shell, larger ones are called venus. Like most bivalves, Mercenaria is a marine species, although many other species of molluscs can also grow in fresh water.
The nature of the contractions of the body of these mollusks (Fig. 14-3) differs significantly from gastropods. clam Mercenaria resembles a laterally compressed gastropod that lacks a head.
The body of the mollusk is located between two shell valves fastened on the dorsal side. When the adductor muscles contract, the shell valves close tightly and can remain in this position for a long time. (After relaxation of these muscles, the valves open due to the elastic properties of the shell lock.
Only the leg and siphons can protrude beyond the shell of Mercenaria, through which water enters the gills.
Since most mollusks live in the thickness of the bottom sand or silt, they do not have a formation similar to the brain with its many sensitive and nervous structures, which are necessary for receiving information from the environment.
On the inner surface of the shell there is a mantle, which is clearly visible on the edge. In mollusks, this tissue secretes shell material and forms two siphons that circulate water through the mantle cavity, which contains the gills and leg. Part of the mantle can form a brood chamber, in which the juveniles of some bivalves develop, although Mercenaria does not have such a structure.
The mollusk can quickly retract the leg, siphons and other soft parts of the body into the shell, but again pushes them much more slowly. This is because the listed 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 equalizes.
The pelecypod mollusk burrows with its foot into wet sand or silt.
Mollusk Ensis (sea stalk) and species close to it tear sand much faster than a person can do even with a shovel. At first, the mollusk plunges the thin end of the leg into the silt, which then fills with blood and unfolds, forming an anchor similar to a mushroom (Fig. 14-4). When the muscles of the body contract, the shell is pulled up to the end of the leg, which is fixed in the silt, and thereby sinks into the thickness of the bottom. Then the leg is inserted 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 vary considerably in structure and function between species. In Mercenaria, the gills consist of two pairs of freely hanging folds located on both sides 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 consist of W-shaped inner and outer records(leaves). Between the two plates is free space divided vertically into a series of narrow, water-filled tubes. Countless cilia vibrating on the surface of the gills direct water towards them, forcing it through one siphon and throwing it out through the other. As water passes through the gills, oxygen and carbon dioxide are exchanged.
The gills also function as "gatherers" of food. The water passing through the gills contains small organisms and organic particles. The mucous membrane constantly formed on the surface of the gills, as a result of the movement of particles, moves ventrally and collects food. Surrounded by mucus, food enters a small, ciliated food groove, through which it is delivered to the mouth and swallowed. Thus, it can be seen that mollusks have adapted to a semi-sessile mode of existence, in which all the necessary substances are delivered from the environment. Mercenaria can move within a limited zone, although, undoubtedly, the mollusk spends most of its life in one place, buried in silt.
Mercenaria are separate organisms. The formation of gametes in these mollusks 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 the siphon, are released into the sea, where fertilization takes place.
14.5. For humans, bivalve mollusks serve as one of the sources of food, and, for example, the "shipworm" mollusk is only a source of trouble.
Like other marine mollusks, fertilized eggs Mercenaria develop into a mobile larva - a trochophore or veliger. These ciliated larvae are found near the water surface and often drift long distances from their parent's habitat, aiding the spread of this species;
After a certain period of time, they undergo metamorphosis and become adults.
Mollusks and related forms are used by man as a source of food. Even in ancient times, shellfish and squid were eaten, and today, despite pollution and devastating prey, which constrain 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. Shellfish are used to obtain dyes, as an additive to poultry feed, in road construction, for the manufacture of buttons and jewelry.
Torado bivalve molluscs (woodworm) cause significant harm to humans by destroying wood. They sieve the underwater parts of rafts, wharves and ships, causing damage of a billion dollars a year.
14.6. The Loligo squid is one of the most common cephalopods, or cephalopods.
All cephalopod mollusks are inhabitants of the seas. Many of them, such as squid and nautilus, live at great depths. The octopus prefers depressions and caves in relatively shallow areas of the sea.
The sizes of cephalopods range from microscopic squid found in plankton to giants up to 20 m long and weighing up to 2 tons. Researchers believe that there were larger specimens that were not only the largest among all known invertebrates, but, perhaps, and the largest animals in general.
Loligo squid (Fig. 14-5) has an elongated body. It does not have an external shell, and the function of the skeleton is performed by a thin internal horny rod.
The squid's leg has been transformed into 10 processes equipped with suckers, of which two are tentacles. In the region of the head are two well-developed eyes, which bear 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 keratinized beak and radula. The saliva secreted in the mouth is poisonous and apparently serves to immobilize prey. The beak is very hard, with which 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, located on the sides of the body, are formed from the fabric of the mantle. They provide swimming and stabilize the position of the body 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 the squid for locomotion. It happens in the following way. Water enters the mantle cavity through its open neck or collar. Then the collar closes, the muscles of the mantle contract sharply and a jet of water is thrown out through the siphon, pushing the squid far away. By turning the siphon in different directions, the squid can move quickly in any direction. Apparently, he uses this mode of transportation only in special occasions, usually swimming with the help of fins.
When irritated, squids and octopuses can release a black liquid from a special gland located in the mantle cavity. This inky puff disorients their potential enemies and can be poisonous.
In addition, squids and octopuses avoid predators by blending into the background of the environment. In the skin of these animals there are cells - chromatophores, capable of changing the location of the pigment, from which the color of the integument of the animal changes. This allows them to acquire different color shades. In some conditions, the animals become pink, in others - pale gray. Such a system not only provides a protective coloration, but, in addition, is used in the mating season and in defensive actions.
Courtship and mating in squids (and in octopuses) are very complex behavioral acts. The male has one specially modified tentacle with which he transfers sperm clods from his mantle to the female's mantle. Fertilization takes place inside the body of the female and subsequently a mass of eggs is released to the outside through her siphon. The female grabs them with her tentacles and molds them into long cords, "fingers of the dead", which she attaches to stones. Such a sequence of actions in 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 have been experimentally removed immediately after leaving the siphon. This type of instinctive behavior is observed in many insects, birds and mammals. Once a behavioral process has begun, these animals cannot stop or change it. They must complete this process completely, even if it has become useless.
Cephalopods have a well developed nervous system. Octopuses are able to distinguish between visual and tactile stimuli, and they can even be trained to respond in specific ways to different stimuli. The great similarity between the eyes of squid and humans is surprising (Fig. 14-5).
Loligo has a giant nerve axon (nerve process) 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 established in experiments carried out on this nerve process. This axon was discovered in 1930, and soon the researchers, introducing electrodes into nerve cells, were able to study the electrical changes during the conduction of a nerve impulse.
14.7. The presence of similar features that are observed in annelids, mollusks and arthropods suggests that they all originated from related organisms.
Despite the insufficient amount of data to establish a common ancestor of annelids, mollusks and arthropods, all these three groups of animals have a large number of similar features.
In particular, polychaetes and mollusks form a larva - a trochophore, and the embryonic development of their coelom occurs in almost the same way. However, the body of molluscs is never segmented. It was believed that the mollusk Neopilina (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. Many living specimens of these small mollusks have been caught at a depth of two kilometers 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 molluscs.
The relationship between annelids and arthropods is evident. 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 emerges from the dorsal brain, or ganglion. In addition, the development of the coelom in these two groups is carried out in parallel ways. Further evidence for a link between the two phyla is the existence of a small phylum of tropical worm-like organisms, Onychopora. Like annelids, these "walking worms" have a soft, segmented body with repeating groups of muscles and nephridia. Like arthropods, they have a dense chitinous cuticle, a tracheal respiratory system, and paired "walking" limbs ending in claws. The limbs of Onychopora do not have joints like those of arthropods, but, like spiders and centipedes, their limbs move through the interaction of flexor muscles (for lifting the limbs) and hydraulic pressure (for extension, since there are no extensor muscles). The most ancient Onychopora lived about 500 million years ago, during the Cambrian period, when arthropods evolved rapidly due to competition with annelids.
