Order Copepods, or Pelican-like - Pelecaniformes. Order Copepoda (Copepoda) Species of copepods

Copepods, or copepods (lat. Copepoda)- a subclass of crustaceans from the class Maxillopoda. One of the largest taxa of crustaceans (according to various sources, the number of copepod species ranges from 10 to 20 thousand). Science studying copepods - copepodology (section of carcinology).

There is a World Society of Copepodologists. World Association of Copepodologists), publishing the newsletter " Monoculus copepod newsletter».

External structure

Diversity of body shape of copepods (drawing by E. Haeckel)

Dimensions

Body Shape

Kalanoid, fam. Diaptomidae

Body parts

The body of copepods is divided into three tagmas: the head - the cephalosome (in copepodology it is sometimes called the cephalothorax, cephalothorax), the chest (thorax) and the abdomen (abdomen). In this case, many copepodologists call the telson (anal lobe) the last abdominal (anal) segment.

The body of copepods can “fold” in half, bending in the sagittal plane. In this case, the boundary between the functionally anterior part of the body (prosoma) and the functionally posterior (urosome) in cyclopoids and harpacticids passes between the thorax segments bearing the fourth and fifth pairs of legs. These groups are united under the name “Podoplea” - “foot-bellied”. In calanoids, the border between the prosoma and the urosome passes behind the segment bearing the fifth pair of legs, which is why they are called “Gymnoplea” - “hollow-bellied”. This character, which correlates well with other structural features, is given high taxonomic weight, and Podoplea And Gymnoplea are considered as taxonomic categories (in modern classifications of copepods - as superorders).

Head and its appendages

The head bears single-branched antennae 1 (antennae, whiskers), bibranched antennae 2 (antennae), mandibles, maxillae 1 (maxillae), maxillae 2 (maxillae) and maxillipeds (maxillae) - appendages of the first thoracic segment fused with the head. In representatives of most families of harpacticids and in some representatives of other orders, the next segment of the chest is fused with the head, bearing swimming limbs, which can be greatly modified.

On the head, between the mandibles, there is a mouth opening, covered in front by a large upper lip, and behind by a small lower lip. On the anterior edge of the head there is a downward-directed outgrowth - the rostrum, sometimes detached.

Antennas I (antennales) are always single-branched. The number of their segments varies among representatives of different orders. Thus, harpacticids usually have 5-8 segments (in males up to 14); most calanoids have 21-27 segments; Cyclopoids have from 9 to 23 segments. In typical representatives, the relative length of the antennules differs: in calanoids they are approximately equal to the body, in cyclopoids they are equal to the cephalothorax, and in harpacticids they are noticeably shorter than the cephalothorax. Antennae I are involved in locomotion and also bear sensilla.

Antennae II are usually bibranched (in many cyclopoids they are single-branched) and are involved in the creation of water currents for swimming and feeding.

The mandible is divided into a coxa, which forms a masticatory outgrowth (gnathobase) with teeth and setae, and a palp, which initially consists of a base, exo- and endopodite. Often the branches, and sometimes the base of the palp, are reduced. Thus, in many Cyclops, only three setae extend from the mandible, which are considered the vestige of a palp.

The chewing teeth of the mandibles of many marine copepods have silica “crowns” that help them chew through the tough houses of diatoms.

Breasts and appendages

On the four segments of the chest following the maxillary segment there are two-branched swimming limbs - flattened legs that serve as the main engines when swimming, for the presence of which the detachment received its name. The swimming limb consists of a two-segmented protopodite, the basal (proximal) segment of which is called the coxa, and the distal one is the basis, and two branches extending from the basis (sometimes it is believed that the protopodite includes another segment - the precoxa, which is weakly separated from the body). The outer (exopodite) and inner (endopodite) branches consist of 2-4 segments each and bear long setae covered with long thin processes (setulae) and shorter spines.

On the last segment of the chest there is a fifth pair of thoracic legs, which are usually not involved in swimming and in many groups are greatly reduced or modified. In males of most calanoid families they are sharply asymmetrical. The endopodites of both legs are often rudimentary, the exopodite of one of the legs serves to transfer the spermatophore to the sperm receptacles of the female during mating, and the larger exopodite of the other limb carries a long claw-shaped curved spine, which is involved in holding the female. The structure and armament of the fifth pair of legs for cyclopoids and calanoids serves as the most important taxonomic character.

Abdomen and its appendages

The abdomen usually consists of 2-4 segments (not counting the telson). On the first segment of the abdomen there are paired genital openings. In harpacticids and cyclopoids it has a rudimentary sixth pair of legs; in calanoids it is limbless. The remaining segments of the abdomen do not bear limbs. On the telson there are two movable appendages - the fork, or furca (furcal branches). These appendages consist of a single segment and are not homologous to the limbs. The furca contains furcal setae, the length and location of which is an important taxonomic character.

Sexual dimorphism

As a rule, in females the first and second abdominal segments fuse, forming a large genital segment; in males this fusion does not occur, so males have one more abdominal segment than females.

In representatives of Cyclopoida and Harpacticoida, males are usually noticeably smaller than females, have hook-shaped, shortened antennae I, which serve to grasp and hold females during mating.

In many Calanoida, females and males do not differ in size. Males have one modified antenna I, called the geniculating antenna. It is expanded in the middle part and can be “folded in half”; like the Cyclops, it serves to hold the female during mating.

In some cases, sexual dimorphism is observed in the structure of almost any pair of limbs and body segments.

Internal structure

Veils

Nervous system and sensory organs

Central nervous system consists of the brain and the ventral nerve cord connected to it by the peripharyngeal nerve ring. An unpaired nerve departs from the brain to the nauplial eye and paired nerves to the frontal organ, as well as nerves to the antennules and antennae (the latter from the tritocerebrum). The subpharyngeal ganglion includes the ganglia of the mandibles, first and second maxillae. The ganglia of the ventral nerve cord are poorly demarcated from each other. The entire abdominal nerve chain is located in the cephalothorax; it does not extend into the abdomen.

Nutrition

Most free-living copepods feed on single-celled or small colonial algae, which they filter through the water column, as well as benthic diatoms, bacteria and detritus, which they may collect or scrape from the bottom. Many species of calanoids and cyclopoids are predators, eating other types of crustaceans (juvenile copepods and cladocerans), rotifers, insect larvae of the first and second instars (including chironomid and culicid larvae), etc. The copepodite stages of some freshwater cyclopoids climb into the brood chambers of Daphnia, where they eat eggs.

A more detailed study of the “filtration” feeding of copepods using high-speed micro-filming revealed that many of them “hunt” individual algae cells, which they catch one by one. Algae-eating copepods store food energy in fat droplets that are contained in their tissues and are often yellowish-orange in color. In polar species that feed primarily on diatoms, during the period of mass spring “blooming” the volume of fat reserves can reach half of the body volume.

Reproduction and development

Mating is preceded by complex sexual behavior, in which, apparently, they usually play important role both chemoreception and mechanoreception. Female copepods secrete sex pheromones, which are perceived by males using chemosensory setae (aesthetascus) of the first antennae.

When mating in most calanoid families, the male first grabs the female by the telson or furcal branches using the geniculate antenna, then by the area of ​​the body located in front of or immediately after the genital segment using the legs of the fifth pair, while the male and female are usually positioned “head to tail” " each other . Mating lasts from several minutes to several days.

Free-living copepods have spermatophore fertilization. Large calanoid spermatophores, comparable in size to the size of the animal’s abdomen, are transferred to the female’s genital segment during mating using the male’s left heel; at its end there are “tweezers” that hold the bottle-shaped spermatophore by the narrowed basal part.

Role in ecosystems

Copepods play an extremely important role in aquatic ecosystems and throughout the biosphere. Apparently, they have the largest biomass among all groups of aquatic animals and almost certainly occupy first place in terms of their share in the secondary production of water bodies. As consumers of phytoplankton, copepods are the main consumers of the first order in the seas and fresh waters. Copepods serve as the main food for many other aquatic animals, from

Free-living, harmless copepods are usually translucent and reach a length of 3mm. They move in short leaps, but can also lie on underwater surfaces, including on the glass of an aquarium, where they are introduced either intentionally (as live food) or accidentally (on plants). Few manage to survive in an aquarium for a long time - for most fish this is a real delicacy. Is it true, large fish They don’t pay attention to them - after all, they are too small and not worth eating. Thus, contamination of an aquarium with free-living copepods can only occur if the fish do not eat them - either because they are unsuitable food, or because the fish are so unwell that they have lost interest in even such a tempting food source . This may be due to environmental pollution (heavy organic load). If copepods begin to reproduce in the aquarium, it means there is organic pollution.

If you eliminate the problem that caused this behavior of the fish, then the fish will solve it themselves with great pleasure.

Cyanobacteria

This is a group of microorganisms that causes the growth of a substance resembling algae. Aquarists call it "blue-green algae." The appearance of such “algae” is associated with high level content of nitrates and phosphates. True, not all aquariums with a large amount of organic waste are filled with these “algae”. In one night they can cover all decorative objects in the aquarium, including the soil, with a slimy bluish-green coating. There is no evidence that they cause direct harm to adult fish (but they may be harmed by poor quality water, which caused the rapid proliferation of cyanobacteria). However, these “algae” can very quickly cover and suffocate fry lying on the ground or decorative objects. In addition, they can completely cover plants and destroy them.

It is very difficult to completely get rid of blue-green algae. Subsequently, at the slightest deterioration in water quality, they can again begin to multiply rapidly. The only way out is to reduce the amount of organic waste and filter out as much of this green matter as possible each time during the next partial water change. Unfortunately, blue-green algae seems completely unpalatable to fish. It is said that sand snails feed on these algae, but none of the authors of this book can confirm this from their own experience. In addition, these snails create no less nuisance than the cyanobacteria themselves (see the “Snails” section).

Hydras

These small coelenterates are freshwater relatives sea ​​anemones. They can be from 2mm to 2cm in length (including tentacles). They have the shape of a stem, topped at one end with tentacles, while the other end is attached to a solid base. All these signs make it possible to unmistakably recognize them. However, sometimes they shrink into tiny jelly-like balls. Their color can vary from cream to gray or light brown. (There are hydras of a pleasant green color, which can easily be mistaken for algae. - Consultant's note.).

Hydra hydras sometimes end up in the aquarium along with live food or decorative items collected from nature. Subsequently, they settle on some objects or aquarium glass and represent additional interesting objects, almost as charming as the main inhabitants of the aquarium.

Hydras are safe for adult fish, but they can catch fry and other small fish, as well as small particles of fish food. Sometimes their numbers reach such a level that they become real pests. Like many other pests, they indicate problems with aquarium maintenance.

To completely destroy hydras, you have to completely empty the aquarium, scrape all its surfaces, wash gravel, decorative objects and underwater equipment in a hot 2-5% saline solution at a temperature above 40 ° C. If the aquarium is planted, then these plants are unlikely to respond well to cleaning in hot salt water! Therefore, it is better to use an alternative method, which consists in removing all fish from the aquarium (as well as snails, if they are desirable inhabitants of the aquarium) into some temporary room and raising the temperature of the water in the aquarium to 42 ° C for half an hour. During heating, the filler that serves as a substrate for bacteria should be removed from the internal filters, but it is better to leave the filters in place, because hydra attaches to their surface. External filters should be turned off, but not for more than an hour, otherwise the bacterial population may die due to lack of oxygen. Then the aquarium should be allowed to cool to normal temperature or cooled by partially changing the water, adding cold water. After this, you can start the fish (and snails) again and restore filtration.

In an aquarium stocked with fish, the hydra population can be controlled by dissolving table salt in the water - you should get a 0.5% saline solution (see Chapter 27). This solution should be maintained for about a week, and then gradually get rid of the salt through repeated partial water changes. This method can only be used if all fish tolerate this salinity well. Otherwise, you will have to regularly clean the glass of the aquarium, filter out separated hydras, and remove stones and other solid decorative objects from the aquarium and treat them in hot salt water.

Some species of fish feed on hydras (especially gourami, as well as young cichlids “grazing” on the rocks). Therefore, they can be used to control the hydra population, but only if these fish are suitable inhabitants for the aquarium in question.

The body of free-living copepods is divided into the cephalothorax, thorax and abdomen (Fig. 202). The head is fused, without any traces of segmentation, fused with the first thoracic segment, forming the cephalothorax. The anterior end of the head is often extended into a downturned beak, or rostrum. The absence of paired compound eyes is very characteristic; Only the nauplial ocellus is located on the frontal part of the head. It was this circumstance that allowed the Danish naturalist Müller to call ordinary freshwater copepods “Cyclops” in honor of the one-eyed giant of Greek mythology.

The head is equipped with 5 pairs of appendages. The anterior antennae are often very long, sometimes longer than the body, and are involved in swimming and soaring of crustaceans. In addition, they also perform the functions of sensory organs: sensitive bristles and cylindrical sensory appendages sit on them. The posterior antennae are short, usually biramous. The mandibles are powerful and have a two-branched palp. Their chewing, highly chitinized part has sharp teeth that help crush food. A careful examination of the teeth of the mandibles of some marine copepods revealed that these teeth are covered with flint crowns, which increase their strength (Fig. 203). The discovery of flint crowns is interesting in two respects. Firstly, it indicates the ability of copepods to assimilate and concentrate silicon; Almost all higher invertebrates - worms, mollusks, and other arthropods - lack this ability.

Secondly, one can hope to find in geological deposits flint crowns of ancient copepods, which are almost completely not preserved in fossil form.

The anterior jaws of copepods are very complex, as they are equipped with internal and external lobes and numerous feathery bristles. The hind jaws have only internal lobes and also numerous setae. The cephalic appendages are joined by a pair of single-branched jaws belonging to the anterior thoracic segment fused with the head.

The posterior antennae, palps of the mandibles and anterior jaws of filter-feeding copepods make frequent and continuous strokes, creating water cycles that bring suspended food particles. These particles are filtered out mainly by the bristles of the posterior jaws.

The thoracic region consists of 5 segments with clearly visible boundaries between them. All 5 pairs of thoracic legs in primitive copepods are constructed identically. Each leg consists of a 2-segmented main part and two usually 3-segmented branches armed with spines and setae. These legs make simultaneous strokes, acting like oars and pushing the crustacean's body away from the water. In many more specialized species, the male's fifth pair of legs is transformed into an apparatus adapted to hold the female during mating and attach spermatophores to her genital openings. Often the fifth pair of legs is reduced.

The abdominal region consists of 4 segments, but in females their number is often smaller, since some of them merge with each other. A paired or unpaired genital opening opens on the anterior abdominal segment, and in the female this segment is often larger than the rest. The abdomen ends in a telson, with which the furcal branches are articulated. Each of them is armed with several very long, sometimes feathery bristles. These setae are especially strongly developed in planktonic species, in which they are adapted for soaring in water, as they prevent the crustacean from immersing.

Copepods breathe over the entire surface of the body; there are no gills. This may also be due to poor development or even absence circulatory system. Only representatives of the suborder Calanoida have a heart, and even in them it is small, although it beats very quickly: for example, in the sea crustacean Labidocera it makes more than 150 beats per minute. In other copepods, the cavity fluid is driven by intestinal contractions.

During mating, the male holds the female with the fifth pair of thoracic legs and the first antennae and, using the same fifth pair of legs, glues the sausage-shaped spermatophore near her genital openings, i.e., to the underside of the first abdominal segment. In some species, one of the branches of the fifth pair of legs of the male is equipped at the end with forceps, which capture the spermatophore and transfer it to the desired place (Fig. 204). From the spermatophore, the sperm enters the female's seminal receptacle. When the eggs are laid, they are fertilized.

Rice. 204. Mating Calanoida: 1 - attachment of the spermatophore to the genital segment of the female in Diaptomus; 2 - fifth pair of legs of Pareuchaeta glacialis; last segment of the left leg with “tweezers” holding the spermatophore

A nauplius larva emerges from the egg. The larva molts repeatedly and gradually approaches the characteristics of an adult crustacean. There are 12 larval stages of copepods. The first two stages - orthonauplius - are characterized by the presence of only both pairs of antennae and a pair of mandibles; in the next four stages - metanauplius - the remaining oral appendages are laid down and develop, but the body remains unsegmented. The last 6 stages are called copepodite and are distinguished by segmentation of the posterior end of the body and the gradual development of the thoracic legs. To complete metamorphosis, different copepods require different times, and the biology of the larvae is not the same in all species.

The lifestyle, feeding method and habitat of copepods are so diverse that it is better to consider this order not as a whole, but each of its suborders separately.

Calanoida are exclusively planktonic animals. Their head and chest are much longer than the narrow abdomen, the anterior antennae are very long, exceeding the head and chest, and often the entire body of the crustacean; if there is an egg sac, then only one.

Harpacticoida, with a few exceptions, live on the bottom and crawl more than swim. Their body is worm-shaped due to the fact that the abdominal region is almost the same in width from the thoracic region. The anterior antennae are very short; females of most species form a single egg sac. Representatives of all three suborders inhabit both seas and fresh waters.

Suborder Calanida

The entire Calanoida organization is excellently adapted to life in the water column. The long antennae and feathery setae of the furcal branches allow the marine Calanus or freshwater Diaptomus to float motionless in the water, only sinking very slowly. This is facilitated by drops of fat located in the body cavity of the crustaceans, which reduce their specific gravity. During hovering, the crustacean’s body is positioned vertically or obliquely, with the front end of the body located higher than the rear. Having dropped a few centimeters down, the crustacean makes a sharp swing with all its thoracic legs and abdomen and returns to its previous level, after which everything is repeated all over again. Thus, the path of the crustacean in the water is drawn with a zigzag line (Fig. 205, 1). Some marine Calanoida, such as the near-surface bright blue species Pontellina mediterranea, make such sharp leaps that they jump out of the water and fly through the air like flying fish.

If the thoracic legs act from time to time, then the posterior antennae, palps of the mandibles and anterior jaws vibrate continuously with a very high frequency, making up to 600-1000 beats every minute. Their swings cause powerful water circulation on each side of the crustacean’s body (Fig. 205, 2). These currents pass through the filtration apparatus formed by the bristles of the jaws, and the filtered suspended particles are pushed forward to the mandibles. The mandibles crush the food, after which it enters the intestines.

All organisms and their remains suspended in water serve as food for filter-feeding Calanoida. Crustaceans do not swallow only relatively large particles, pushing them away with their jaws. The basis of nutrition for Calanoida should be considered planktonic algae, consumed by crustaceans in huge quantities. Eurytemora hirundoides, during the period of massive development of the alga Nitzschia closterium, ate up to 120,000 individuals of these diatoms per day, and the weight of the food reached almost half the weight of the crustacean. In cases of such excess nutrition, the crustaceans do not have time to assimilate all the organic matter of the food, but still continue to swallow it.

To determine the filtration intensity of Calanus, algae labeled with radioactive isotopes of carbon and phosphorus were used. It turned out that one crustacean passes through its filtration apparatus up to 40 and even up to 70 per day cm 3 water, and it feeds mainly at night.

Eating algae is necessary for many Calanoida. For example, the reproductive products of Calanus finmarchicus mature only when the crustacean has sufficient consumption of diatoms.

In addition to filter feeders, among Calanoida there are also predatory species, most of which live at significant or great ocean depths, where planktonic algae cannot exist due to the lack of light. The hind jaws and mandibles of these species are equipped with strong, sharp spines and are adapted for grasping victims. Particularly interesting are the adaptations for obtaining food in some deep-sea species. Winkstead observed how the deep-sea Pareuchaeta hung motionless in the water, spreading its elongated jaws to the sides, forming something like a trap (Fig. 206). As soon as the victim is between them, the jaws close and the trap slams shut. With the extreme sparseness of organisms at great ocean depths, this method of hunting turns out to be the most appropriate, since the expenditure of energy on active searches for prey is not repaid by eating them.

Rice. 206. Opened "trap" Pareuchaeta

Calanoida is associated with the peculiarities of movement and nutrition complex problem their daily vertical migrations. It has long been noticed that in all bodies of water, both fresh and sea, huge masses of Calanoida (and many other planktonic animals) rise closer to the surface of the water at night, and sink deeper during the day. The scope of these daily vertical migrations varies not only among different types, but even in one species in different places its habitat, in different seasons of the year and in different age stages of the same species. Often, nauplii and younger copepodite stages always remain in the surface layer, while older copepodite stages and adult crustaceans migrate. In the northern part Atlantic Ocean the vertical migration range of Calanus finmarchicus is 300-500 m. The Far Eastern Metridia pacifica and M. ochotensis cover the same enormous distances every day. At the same time, other widespread Far Eastern Calanoida - Calanus plumchrus, C. cristatus, Eucalanus bungii - migrate no more than 50-100 m.

The speed of movement of crustaceans during their vertical migrations is measured in values ​​of the order of 10-30 cm in a minute. If we take into account the length of their body (for Calanus finmarchicus, for example, about 2 mm), then such a speed must be considered significant. In this case, not only the upward movement, but also the lowering down is carried out due to the active movements of the crustaceans, and not due to their passive immersion.

One should not think that when performing vertical migrations, all crustaceans simultaneously move in any particular direction. The English scientist Bainbridge went underwater and made observations of migrating copepods.

He saw how, in the same layer of water, some crustaceans move up and others move down. Depending on which movement predominates, the entire mass of animals moves up or down.

The question of the reasons for vertical migrations has not yet been fully clarified. It is quite obvious that the desire of crustaceans to rise to the surface layers is explained by the abundance of planktonic algae there, which filter-feeding copepods feed on. Less clear are the reasons that force crustaceans to leave these food-rich layers. Many researchers believe that light has a harmful effect on crustaceans and, avoiding it, they begin to go down in the morning. The importance of light is confirmed by V. G. Bogorov’s observations of the vertical distribution of copepods in the Barents Sea in summer, i.e., under 24-hour lighting conditions. It turned out that at this time Calanus finmarchicus is invariably located at the same depth, where the lighting conditions are most favorable for it. In this area of ​​the sea, internal waves are observed in the water column, which should either raise or lower the crustaceans somewhat. Obviously, the crustaceans actively move in the opposite direction, since they do not go beyond a certain horizon throughout the day. In autumn, when the cycle of day and night is restored, normal vertical migrations resume (Fig. 207). Not only sunlight, but also moonlight forces crustaceans to move from the surface layers of water to deeper ones.

However, not in all cases can vertical migrations be associated directly with the action of light. There are observations showing that crustaceans begin to descend long before sunrise. Esterly kept the copepods Acartia tonsa and A. clausi in complete darkness, and despite this, they continued to make regular vertical migrations.

According to some scientists, the departure of crustaceans in the morning from the illuminated layer of water should be considered a protective reaction that helps avoid being eaten by fish. It has been proven that fish see every crustacean they attack. Having descended into the deep dark layers of water, the crustaceans are safe, and in the algae-rich surface layers at night the fish also cannot see them. These ideas cannot explain many well-known facts. For example, a number of copepods make regular migrations of short distances, without leaving the illuminated zone and, therefore, remaining accessible to planktivorous fish.

In addition to daily vertical migrations, marine copepods also perform seasonal migrations. In the Black Sea in summer, the temperature of the surface layer rises, and Calanus helgolandicus living there drops by approximately 50 m, and in winter it returns to shallower depths. In the Barents Sea, young stages of C. finmarchicus remain in the surface layers in spring and summer. After they grow up, in autumn and winter the crustaceans move down, and before spring, individuals that reach maturity begin to rise to the surface, where a new generation hatches. Particularly numerous in the surface layers are crustaceans located at the IV-V copepodite stages and known as “red calanus”, as they contain a large amount of brownish-red fat.

"Red calanus" is a favorite food of many fish, in particular herring. A similar nature of seasonal migrations, i.e., ascent to the surface layers of water for reproduction, has been found in many other mass species, for example, in Calanus glacialis, C. helgolandicus, Eucalanus bungii, etc. Females of these species require abundant nutrition of algae, and possibly lighting, for the development of reproductive products. Other species (Calanus cristatus, C. hyperboreus), on the contrary, reproduce in deep layers, and only their juveniles rise to the surface. Adult crustaceans C. cristatus do not feed at all; in sexually mature individuals, the mandibles are even reduced. The length of seasonal migrations is usually longer than daily migrations. The former sometimes cover 3-4 thousand meters, and the latter - at most several hundred meters.

Representatives of the suborder Calanoida are predominantly marine animals. Currently, about 1,200 marine species of these crustaceans are known, belonging to 150 genera and 26 families. Only about 420 species live in fresh waters, distributed among 12 genera and 4 families.

Recent detailed studies of the fauna of sea calanids have shown that previous ideas about the wide distribution of many species of these crustaceans are incorrect. Each part of the ocean is inhabited mainly by species unique to it. Each species of sea calanids spreads thanks to currents carrying crustaceans. For example, branches of the Gulf Stream entering the Polar Basin bring calanids from the Atlantic Ocean there. In the northwestern part of the Pacific Ocean, some species live in the waters of the warm Kuroshio Current, and others live in the waters of the cold Oyashio Current. It is often possible to determine the origin of certain waters in certain parts of the ocean based on the calanid fauna. Water fauna differ especially sharply in their composition temperate latitudes and waters of the tropics, and the tropical fauna is richer in species.

Calanids live at all oceanic depths. Among them, there is a clear distinction between surface species and deep-sea species that never rise to the surface layers of water. As already indicated, predators predominate at great depths, and filter feeders predominate at shallow depths. Finally, there are species that perform vertical migrations of a huge range, sometimes rising to the surface, sometimes descending to a depth of 2-3 km.

Some shallow-water species of calanids in temperate waters develop in huge numbers and, by weight, constitute the predominant part of the plankton. For example, plankton Barents Sea approximately 90% consists of Calanus finmarchicus (Table 31, 3). These crustaceans are characterized by high nutritional value: their body contains 59% proteins, 20% carbohydrates and often more than 10-15% fats. Many fish, as well as baleen whales, feed mainly on calanids. These are, for example, herring, sardine, mackerel, anchovy, sprat and many others. One herring was found to contain 60,000 copepods in its stomach. The whales that actively consume huge masses of calanids are fin whales, sei whales, blue whale and humpback.

Calanoida of inland water bodies resemble in their biology marine species. They are also confined only to the water column, also perform vertical migrations and feed in the same way as marine filter feeders. They live in a wide variety of water bodies. Some species, such as Diaptomus graciloides and D. gracilis, live in almost all lakes and ponds in the northern and central parts of the USSR. Others are confined only to the Far East or to the southern part of our country. The distribution of Limnocalanus grimaldii, which inhabits many lakes in the north of our country (including Onega and Ladoga) and Scandinavia, is very interesting. This species is close to the coastal brackish-water L. macrurus, which lives in the pre-estuary spaces of northern rivers. The lakes inhabited by L. grimaldii were once covered by the cold Ioldian Sea. In Baikal, the crustacean Epischura baicalensis, unique to this lake, lives in huge numbers and serves as the main food for omul. Very peculiar, although still little known, are the conditions of existence of the recently discovered only underground representative of calanids - Speodiaptomus birsteini.

This blind crustacean was found in the deep and narrow water-filled crevices of the lower floor of the Skelskaya Cave, located in the Crimea, near Sevastopol. We managed to observe him in an aquarium, and it turned out that he swims in the same way as ordinary freshwater calanids. It remains a mystery what it feeds on as it filters the clean, completely algae-free and probably very bacteria-poor underground pool water. Apparently, it can be considered the only true underground planktonic animal.

Some freshwater calanids appear in water bodies only at certain times of the year, for example in spring. In spring puddles one often finds relatively large ones (about 5 mm) Diaptomus amblyodon, colored bright red or blue. This species and some other widespread freshwater calanids are capable of forming resting eggs that can withstand drying and freezing and are easily carried by the wind over long distances.

Suborder Cyclops (Cyclopoida)

Another suborder of copepods, Cyclopoida, is represented by the largest number of species in fresh waters.

Freshwater cyclops live in all kinds of bodies of water, from small puddles to large lakes, and are often found in very large quantities copies. Their main habitat is the coastal strip with thickets of aquatic plants. Moreover, in many lakes certain types of cyclops are confined to thickets of certain plants. For example, for Valdai Lake in the Ivanovo region, 6 plant groups with corresponding groups of Cyclops species are described.

Relatively few species can be considered true planktonic animals. Some of them, belonging mainly to the genus Mesocyclops, constantly live in the surface layers of water, others (Cyclops strenuus and other species of the same genus) make regular daily migrations, descending during the day to a considerable depth.

Cyclops swim somewhat differently than calanids. Simultaneously flapping four pairs of thoracic legs (the fifth pair is reduced), the crustacean makes a sharp jump forward, upward or sideways, and then, with the help of the front antennae, can hover in the water for some time. Since the center of gravity of its body is shifted forward, while hovering its front end tilts and the body can assume a vertical position, and the dive slows down. A new swing of the legs allows the Cyclops to rise. These swings are lightning fast - they take 1/60 of a second.

L. Isaev, who has been extensively involved in the biology of cyclops, describes their movements as follows: “Moving in rhythmic leaps, a cyclops can stay well at one level, rise up and fall down at angles of varying steepness. A cyclops can swim with equal ease, turning over on its back. The cyclops describes well arcs, makes loops, single and multiple, forward and reverse. The Cyclops can make a turn at an angle of 90°, rotate around an axis not only with a descent, reminiscent of the turns of an airplane “corkscrew,” but also with an upward movement. The Cyclops can slide onto the antenna, make a flip through it, dive headfirst at an angle of 90° and glide onto the tail. The nature of the "figures" performed by the Cyclops is very similar to aerobatics. Possession of the aerobatics necessary for fighter aircraft undoubtedly makes it easier for the Cyclops - an active predator - the ability to ensure one’s existence by hunting for aquatic inhabitants that serve as food.”

Most cyclops are predators, but there are also herbivorous species among them. Such common, widespread species as Macrocyclops albidus, M. fuscus, Acanthocyclops viridis and many others quickly swim above the bottom or among thickets in search of prey. With the help of their antennae, at a very short distance, they sense small oligochaetes and chironomids, which they grab with their front jaws armed with spines. The hind jaws and maxillae are involved in transferring food to the mandibles. The mandibles make rapid cutting movements for 3-4 seconds, followed by a minute pause. Cyclops can eat oligochaetes and chironomids larger than themselves. The speed at which prey is eaten depends on their size and the hardness of their coverings. For crushing and swallowing bloodworms 2 long mm it takes 9 minutes, and the larva is 3 long mm destroyed within half an hour. More delicate, although longer (4 mm), the Nais oligochaete worm is eaten in just 3.5 minutes.

Herbivorous cyclops, in particular the common Eucyclops macrurus and E. macruroides, feed mainly on green filamentous algae (Scenedesmus, Micractinium), capturing them in approximately the same way as predatory ones capture worms and bloodworms; in addition, various diatoms, peridinia and even blue-green algae are used. Many species can only eat relatively large algae. Mesocyclops leuckarti quickly fills its intestines with Pandorina colonies (colony diameter 50-75 mk) and almost does not swallow small Chlamydomonas at all.

Freshwater cyclops are very widespread. Some species are found almost everywhere. This is facilitated primarily by adaptations to transfer unfavorable conditions, in particular, the ability of crustaceans to tolerate drying out of water bodies and passively disperse through the air in the form of cysts. The skin glands of many cyclops secrete a secret that envelops the body of the crustacean, often together with the egg sacs, and forms something like a cocoon. In this form, crustaceans can dry out and freeze into ice without losing their viability. In Camerer's experiments, cyclops were quickly hatched by soaking dry mud, which was preserved for about 3 years. Therefore, there is nothing surprising in the appearance of cyclops in spring puddles that appear when snow melts, in newly filled fish ponds, etc.

The second reason for the wide distribution of many species of cyclops should be considered the resistance of crustaceans in an active state to the lack of oxygen in water, its acidic reaction and many other factors unfavorable for other freshwater animals. Cyclops strenuus can live for several days not only in the complete absence of oxygen, but even in the presence of hydrogen sulfide. Some other species also tolerate unfavorable gas conditions well. Many cyclops thrive in water with an acidic reaction, with a high content of humic substances and extreme poverty of salts, for example, in reservoirs associated with high-moor (sphagnum) bogs.

Nevertheless, species and even genera of Cyclops are known that are limited in their distribution by certain certain conditions, in particular temperature and salt conditions. For example, the genus Ochridocyclops lives only in Lake Ohrid in Yugoslavia, the genus Bryocyclops - in Southeast Asia and in equatorial Africa. Close to the last genus is the exclusively underground genus Speocyclops, species of which were found in caves and groundwater in Southern Europe, Transcaucasia, Crimea and Japan. These blind small crustaceans are considered remnants of a once more widespread thermophilic fauna.

Some cyclops have adapted to life in brackish and even very salty bodies of water. The genus Halicyclops, for example, is quite common in the Caspian Sea and is not found in fresh water. Microcyclops dengizicus is widespread only in brackish and saline reservoirs of the desert zone (Iraq, India, Haiti, Egypt, California, in the USSR - in the Karaganda region, in the Mugan steppe) and lives well even at salinities exceeding sea salinity (up to 41 0 / 00). Many common freshwater species can also exist in brackish water, such as Mesocyclops leuckarti in the Gulf of Finland and the Gulf of Bothnia.

Marine representatives of the suborder Cyclopoida are less diverse than freshwater ones. Among them, species of the genus Oithona are common and often numerous in marine plankton. Large ones are also very typical (up to 8 mm) flattened species of the genus Sapphirina, the surface of the body of which is cast in bright blue, golden or dark red tones (Table 31, 1). Another close maritime family- Oncaea (Table 31, 4) - has glands that secrete a luminous secretion, and often, together with other organisms, causes the sea to glow.

Suborder Harpacticoida

Much less is known about the lifestyle of representatives of the third suborder - Harpacticoida. These worm-like, mostly very small crustaceans, are extremely diverse in both marine and fresh waters, but are never found in large numbers. More than 30 families and several hundred species of Harpacticoida have been described.

Most harpacticids crawl along the bottom and bottom plants. Only a few species are capable of swimming for a long time and are part of the marine plankton (Microsetella). Much more typical are entire groups of genera and species of harpacticids, adapted to living in special, unusual conditions, in particular in the capillary passages between grains of sand on sea beaches and in underground fresh waters.

Just a few years ago, zoologists used a very simple technique to study the population of the capillary passages of sea sand. A hole is dug on the beach, above sea level. Water gradually accumulates in it, filling the capillaries of the sand. This water is filtered through a plankton network and thus representatives of a peculiar fauna, called interstitial, are obtained.

Harpacticides constitute a significant part of the interstitial fauna. They were found everywhere where relevant research was carried out - on the beaches of England, along the European and American coasts of the Atlantic Ocean, on the Mediterranean and Black Seas, off the coast of Africa and India, on the islands of Madagascar, Reunion and the Bahamas. Most interstitial harpacticids belong to special genera that live only in such conditions, distinguished by an unusually thin and long body (Fig. 209), allowing the crustaceans to move in narrow capillary passages. It is remarkable that some of these specialized species were found in very widely separated places. So, for example, on Bahamas were Arenosetella palpilabra, previously known only from Scotland, and Horsiella trisaetosa, previously known only from Kiel Bay. It is difficult to explain such a distribution, since interstitial harpacticids do not have resting eggs.

Harpacticides of fresh groundwater are also represented by a number of specialized genera - Parastenocaris, Elaphoidella, Ceuthonectes and others, partly very widespread, partly having narrow and fragmented habitats. For example, two species of the genus Ceuthonectes live only in caves in Transcaucasia, Yugoslavia, Romania, Italy and Southern France. These widely separated locations are believed to be the remnants of what was once a much larger area of ​​distribution of the ancient family. In some cases, the tropical origin of the underground harpacticides of Europe can be assumed. Among the numerous species of the genus Elaphoidella there are both tropical and European species. The former live in terrestrial waters, the latter (with a few exceptions) in underground waters. In all likelihood, underground remains of ancient tropical fauna that died on the surface of the earth under the influence of climate change. In tropical terrestrial water bodies, some harpacticids are adapted to living conditions that resemble those in groundwater. Tropical species of Elaphoidella are known to live in peculiar micro-reservoirs formed in the leaf axils of aquatic plants from the Bromeliaceae family. The tropical Viguierella coeca, found on these plants in botanical gardens in almost all countries, lives in the same conditions.

The peculiar fauna of Baikal is extremely rich in species of harpacticids. It consists of 43 species, of which 38 are endemic to this lake. There are especially many of these crustaceans in the coastal part of Lake Baikal, on rocks and aquatic plants, as well as on the sponges growing here. Apparently, they feed on sponges and, in turn, become victims of the amphipod Brandtia parasitica, which also crawls on the sponges.

Some types of harpacticids are confined only to reservoirs that are very poor in salts, characterized by high acidity, i.e., associated with high-moor, sphagnum, and bogs. Such is, for example, Arcticocamptus arcticus, the biology of which was studied in detail by E. V. Borutsky.

A. arcticus is widespread in northern Europe, from the Bolynezemelskaya tundra to Scandinavia, on the west coast of Greenland, and on Novaya Zemlya. In addition, it was found in the Alps and in several points in the central zone of the European part of the USSR, including in Kosin near Moscow, in Zvenigorod, near Yaroslavl, etc. Everywhere it lives in reservoirs associated with sphagnum bogs.

Of the numerous reservoirs located near Kosin, the crustacean lives only in two swamps and in the Holy Lake, which lies among the sphagnum peat bog. Obviously, the living conditions in various other neighboring water bodies are unfavorable for A. arcticus. Moreover, even in the few reservoirs inhabited by it, the crustacean exists in an active state only for 1 1/2 -2 months in the spring; the rest of the year, i.e. 10-10 1/2 months, it spends in the resting egg stage.

The life cycle of A. arcticus is closely related to changes in the vegetation cover of the swamp. E.V. Borutsky writes: “As soon as the loose snow begins to melt with the first warm rays of spring and puddles form on the surface of the swamp, all animals that have spent a harsh winter in one or another stage in icy confinement begin to react to the first spring rays. A. arcticus is one of the first to emerge from the state of suspended animation and appears in the reservoir. Already in small puddles, still among the snow, where the surface layers of sphagnum have thawed, you can find its larvae, slowly and clumsily moving among the leaves of moss in search of food. Larvae - on the first nauplius stage and, obviously, just hatched from the egg. Every day the nauplius gets stronger, its movements become more confident and faster, finally, the moment of the first molt comes - it changes the old narrow shell to a new, more spacious one. The first molt is followed by the second, the third, etc., and now after two or three weeks we already meet adult specimens or larvae at the last copepodite stage... But they no longer enjoy the space that they had in their early larval state: instead of vast puddles, full of water, in which they swam freely from one sphagnum bush to another, now there is only wet moss and a small amount of water. Instead of pitiful bare branches there are now delicate pink flowers of Cassandra and cranberries, white cups of andromeda and the caps of blooming blasphemy. The swamp has changed - the bright green sphagnum carpet is replete with pink and white spots of flowers. And this change in the picture of the swamp coincides perfectly with certain moment in the biology of A. arcticus, specifically with the copulation period. For several days we meet almost exclusively copulating couples. But these flowers are fatal for A. arcticus: with their gradual withering, a gradual decrease in the number of crustaceans is observed, copulation occurs less and less often, females with egg sacs are more often encountered, and, finally, by the middle or end of June, A. arcticus completely disappears from the reservoir , and only belated specimens are found in small quantities in July or early August."

The crustacean leaves its egg sacs in the reservoir, which have the shape of two balls connected together, covered with a common “bag” shell, which provides mechanical protection for the eggs and also protects them from drying out. In addition, each egg has its own thinner transparent shell. It is impermeable to both salts and water. By autumn, a nauplius is formed in each egg, and the nauplii of two connected eggs are always directed with their anterior ends in opposite directions. Nauplii are covered with another very thin and elastic inner shell, equipped with various cords and threads. This shell is permeable to water, but not to salts.

When the time comes for the nauplii to hatch, i.e., during the spring melting of the ice, a crack forms in the sac shell on one side, through which the elastic inner shell begins to protrude. At first, this process goes very slowly, but after about half of the larva surrounded by the shell is outside, a sharp push occurs and the larva, enclosed in a hollow ball, seems to “shoot” out of the egg sac and bounces to the side or is held behind the edges of the slit by elastic appendages. shells. It is remarkable that the nauplius itself remains completely passive almost all the time. Only at the very beginning of the hatching process does the nauplius make several rather weak movements, apparently leading to rupture of the egg membrane. The main role here is played by a semi-permeable elastic shell, through which water diffuses, causing it to swell, which first causes the sac shell to burst, and then the nauplius, surrounded by an elastic shell, to bulge out of it. The strands and threads of this shell act like springs, and they are located in such a way that the nauplius inside the hollow ball formed by the shell always comes out with its head end forward. Behind the first nauplius, through the same gap in the sac shell, the second one protrudes in the same way, or both “shoot” at the same time. The first impetus for swelling of the elastic membrane is, apparently, the rupture of the egg shell by the nauplius (Fig. 210).

Only after some time does the newborn nauplius, located inside the completely inflated elastic shell that has taken on a spherical shape, begin to move and try to tear it apart. He does not succeed immediately, after which the shell collapses and the larva is free. Tired of hard work, at first she is almost unable to move quickly, but she does not need this, since she finds a sufficient amount of food on the surface of the just abandoned sac shell, which usually overgrows with algae and becomes covered with detritus particles during its many-month stay in the reservoir.

When A. arcticus eggs were placed in water from reservoirs unfavorable for its existence, the nauplii inside the eggs developed normally, but they did not hatch. Through special experiments, E.V. Borutsky proved that with a relatively high salt content in water, water does not diffuse through the elastic inner shell and it does not swell.

If the water is not acidic, the egg shell does not partially dissolve or soften, which also eliminates the possibility of the nauplius hatching. Thus, both of these shells prevent the nauplius from hatching when the egg gets into conditions unfavorable for the crustacean, dooming it to death. Indeed, larval stages and adult crustaceans died in the water of lower (non-phagnum) bogs, as well as other bodies of water, containing the usual amount of salts and having a neutral or alkaline reaction. All this makes clear the strict confinement of A. arcticus to raised, sphagnum, bogs with their specific hydrochemical regime.

If A. arcticus exists in an active state in the spring, then some other species of freshwater harpacticids are found only in winter or only in summer. At the same time, species are known that spend the resting period not in the resting egg stage, like A. arcticus, but in the cyst stage, somewhat reminiscent of the Cyclops cysts described above. In Canthocamptus staphylinus such cysts are round, in Attheyella wulmeri and A. northumbrica they are oval, with the furcal bristles of the crustacean protruding from the shell (Fig. 211).

Among freshwater harpacticids, there are species capable of parthenogenetic reproduction, which is not characteristic of all other copepods. In Elaphoidella bidens, which is widespread in Europe, males are generally unknown, but under experimental conditions, 5 generations of parthenogenetic females were obtained from this species. Epactophanes richardi also turned out to be capable of parthenogenetic reproduction, although under natural conditions it is represented by both females and males. Apparently, some other species of harpacticids can reproduce parthenogenetically.

The practical importance of harpacticids is incomparably less than that of calanids and cyclops. In some reservoirs they constitute a significant part of the food of fish, especially their juveniles.

Ergasilus larvae emerging from eggs lead a free lifestyle. After 2-2 1/2 months, the crustaceans reach maturity and mate. Fertilized females actively move against the current. This helps them settle on the gills of the fish, since a current of water is directed from under the gill cover.

In the same way, the gills of fish are affected by glochidia of pearl barley (see above). It is interesting that there is antagonism between ergazilides and glochidia: one displaces the other and is not found together on the gills of the same fish.

Here the nauplius molts, turning into a multicellular oval body. Subsequently, this embryo develops two long appendages at the anterior end, which serve to absorb food. The embryo molts again and transforms into a long, sausage-shaped body, inside which an adult crustacean with well-developed genitals is formed. It breaks through the wall of the blood vessel and the integument of the host and begins active existence (Fig. 213).

Representatives of the suborder Caligoida are characterized by an expanded body, flattened in the dorso-abdominal direction, segmentation of the thoracic region is lost to one degree or another, females have a very large anterior abdominal (genital) segment, to which two egg sacs are attached, the oral appendages form a proboscis, which allows them to suck blood owner. Females and males differ little in size and structure.

Herbivorous copepods - Calanoida

Copepoda are the largest and most diverse group of crustaceans. Currently, they include 3 orders (calanoids, cyclops, harpacticids), 210 families, 2300 genera and more than 14,000 species, and this, of course, is not the full number of organisms inhabiting the seas and continental waters, transition zones between water and land, or living in symbiotic relationships with other animals. They are the largest group of multicellular animals on earth, outnumbering even insects, which include more species but fewer individuals!

Copepoda are mobile, playful and relatively large planktonic organisms. With the help of antennae and chest legs, striking them like oars, they “fly” in the water column. Their body is spindle-shaped with a clear division into two parts: the cephalothorax and abdomen, which ends in a furca, resembling a fork. There is an unpaired eye on the head, for which one of their most well-known groups to aquarists is named Cyclops - after the mythical one-eyed giants. Most copepods are predators, attacking even smaller animals. But there are also herbivorous forms - calanoids (Calanoida), which have a larger cephalothorax and a shortened abdomen (see photo). Their anterior antennae are very long (sometimes longer than the body length) and serve as the main organ of locomotion. They feed mainly on algae.

Some species of cladocerans are characterized by cyclomorphosis. Many species are found only during the period of open water, laying resting eggs for the winter - ephippia, from which juveniles emerge in the spring, when the water temperature becomes acceptable. They also use this when living in bodies of water that dry up: they remain in the form of an embryo in the ephippia until the rain passes.
Zooplankton lives in any body of water. In stagnant waters, the zooplankton community - zooplanktonocenosis - is richer both in the number of species and in abundance. Cladocerans, as a rule, do not tolerate currents well, therefore they prefer lakes, ponds, puddles, and reservoirs, but rotifers are better able to withstand dizzying pirouettes in the flow of water, so in rivers, springs, and springs, plankton consists mainly of them.

Zooplankton is of particular importance in lake ecosystems, where its abundance and biomass reach significant values. In rivers, communities of planktonic invertebrates are formed in deep-water sections of the channel with a slow flow, in kuryas, and floodplain reservoirs. On reaches and rifts, where there is no zooplankton as such, planktonic invertebrates are found in the drift and benthos.

Zooplankton and benthos are the main communities of invertebrates that ensure the normal functioning of aquatic ecosystems, their self-purification, and are the food supply for many species of fish. Zooplankton usually consists of three systematic groups of invertebrates: rotifers (Rotatoria), cladocerans (Cladocera), copepods (Copepoda). The same invertebrate taxa are also present in the benthos, but due to the specific nature of the generally accepted benthic sampling, as a rule, rotifers in benthic communities are not taken into account. Most species of crustaceans live both in the water column, being a component of zooplankton, and at the bottom of reservoirs, in benthos. Thus, most calanoids (Calanoida) lead a planktonic lifestyle throughout their entire life, except for the stage of resting eggs; cyclops (Cyclopida) inhabit both the water column and are a component of microzoobenthos; harpacticoids (Harpacticoida) are considered exclusively benthic animals, but are quite often found in plankton. Therefore, when speaking about the biodiversity of zooplankton organisms and their knowledge, we mean the diversity and knowledge of planktonic and benthic rotifers, cladocera and copepods.

Waterbirds of large and medium size, although larger than large ones. The smallest representative of the order in our fauna is the little cormorant, weighing about 800 g, the largest are pelicans - 10-13 kg. Outside our fauna there are smaller copepods - phaetons, approximately the size of a crow or a seagull.

Copepods have a low set on their legs (the tibia and tarsus are short) and are very characteristic structure paws: a well-developed swimming membrane connects all 4 toes, with the hind toe turned slightly forward and inward. The only exceptions are frigate birds, whose swimming membranes are heavily cut out and do not reach the terminal phalanx of the fingers. The legs can be strong, strong, like those of pelicans, or, like frigate birds, they can be so weak that they can practically not be used when moving on a solid substrate. In cormorants, the legs are carried far back, which causes the bird to sit almost vertically when on land. The beaks of copepods are varied. They are either straight, almost conical, sharp, or slightly compressed from the sides, somewhat bent upward, with a strong, downwardly curved nail - the end of the beak, or, finally, wide, strongly flattened, with a highly extensible non-feathered skin throat sac below. The tails of copepods are also varied, consisting of 12-24 tail feathers. different shapes and length. In pelicans, the tail is short, rounded, soft, in cormorants and darters it is long, stepped, hard, in gannets it is long, wedge-shaped, in frigates it is forked with greatly elongated outer tails, and, finally, in phaetons it is long, stepped with elongated tails of the middle pair.

The plumage of copepods is dense and (with the exception of pelicans) close to the body and rigid. Down grows on both pterilia and apteria; apteria are narrow. Those copepods that cannot dive have very high pneumaticity of the skeleton; air cavities are present in almost all bones. There is also a well-developed network of subcutaneous branches of the air sacs, which form an air-bearing layer, especially pronounced on the sides of the body.

Copepods have a very small, vestigial tongue. Their esophagus, glandular and muscular stomachs are highly distensible, which allows them to swallow large prey. Copepods are monogamous birds that live in colonies, often very large, often together with other species, such as herons. Colonies are located near water, but in a wide variety of conditions.

Copepods make nests in trees, bushes, rocks, reed thickets, or directly on the ground. The same nests occupy several years in a row. They are built, and later the eggs are incubated and the chicks are fed by both the male and the female, sometimes the female is larger than the male. In different species there are from 1 to 5-6 eggs in a complete clutch. The chicks hatch naked, blind and helpless, and only after a few days their eyes open and they are covered with thick down. At first, the parents feed the chicks with semi-digested food, which they regurgitate directly into their mouths. Parents also bring water in their beaks for the chicks. Postembryonic development of chicks is long, in pelicans, for example, up to 50-60 days. Copepods become sexually mature at the 3-4th year of life. Most copepods fly very well, with many using soaring flight. Some of them cannot dive (and sometimes even swim).

Some species swim very well and dive well, but fly worse than their non-diving counterparts. Copepods feed on fish and other aquatic animals. Therefore, the question of their possible importance for fisheries, especially in inland waters and deltas big rivers, attracts the attention of many researchers. A number of copepod species have undoubtedly positive economic importance. Pelicans, cormorants and gannets, nesting on secluded and waterless islands in millions of pairs, leave in these places a huge amount of droppings, which accumulate over time in layers of many meters. This is the famous guano, which for several decades served as the main nitrogenous fertilizer for the marginal lands of Western Europe. Its use has made it possible to dramatically increase crop yields in Europe and North America.

On small islands near Peru, for example, where the total number of nesting copepods is now estimated at approximately 35 million, guano deposits reached a thickness of 30 m. Even the ancient Incas knew well the value of this treasure. They used guano in terracing for agricultural purposes on the eastern slopes of the Andes. Copepod nesting sites were carefully guarded, and for visiting them during prohibited times, the violator was subject to the death penalty. Subsequently, after the destruction of the Inca culture by the Spaniards, guano was forgotten, and only in 1840, when the famous German chemist Liebig pointed out the value of this fertilizer for the lands of Western Europe (guano is 33 times more effective than manure), the plunder of natural guano reserves began, accompanied by exceptional scale destruction of nesting colonies of guano-forming birds: tens of thousands of chicks were simply trampled underfoot, eggs were broken, nests were torn down. Flotilla after flotilla went to these islands from Europe and the USA, several tens of millions of tons of fertilizers were selected, several millionaires appeared who became rich from guano, and at the beginning of this century it was discovered that the nesting sites had been cleared, one might say, to a stone.

As a result of the activities carried out in 1950, the islands produced almost a quarter of a million tons of guano, not a single kilogram of which was exported. Thanks to this fertilizer, the thin soils of the Peruvian coast now produce a cotton yield of over 320 kg per hectare, while, for example, in Louisiana (USA) the cotton yield is 55 kg per hectare, in the UAR - slightly more than 70 kg per hectare. The order Copepods as a whole has a cosmopolitan distribution, although some groups inhabit only low latitudes. Currently, this order includes 50 species of birds belonging to 5 sharply defined families: phaetons (Phaethontidae), pelicans (Pelecanidae), gannets (Sulidae), cormorants (Phalacrocoracidae) and frigates (Fregatidae). It is possible that the darters, which are classified as a subfamily of cormorants, should, as some researchers do, be considered an independent family Anhingidae. About 77 fossil species of copepods are known, one species (spectacled, or Steller's, cormorant) became extinct in historical times.