Detachment of copepods. Copepods. Nervous system and sense organs
Order Crustacea Copepods
(COPEPODA)
/ Crustacean copepods //copepoda/
The thoracic region consists of 5 segments with clearly visible boundaries between them. All 5 pairs of pectoral legs in primitive copepods are arranged in the same way. Each leg consists of a 2-segmented main body and two usually 3-segmented branches armed with spines and setae. These legs make simultaneous strokes, acting as oars and pushing the body of the crustacean from the water. In many more specialized species, the male's fifth pair of legs has been modified into an apparatus designed 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 less, 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 others. The abdomen ends in a telson, with which the furcal branches are articulated. Each of them is armed with several very long, sometimes feathery setae. These setae are especially strongly developed in planktonic species, in which they increase the surface of the body (in relation to its volume), which contributes to the soaring of the crustacean and the water column.
SUBORDER CALANOIDA 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 Galanus or the freshwater Diaptomus to hover motionless in the water, only sinking very slowly. This is facilitated by fat drops located in the body cavity of crustaceans, which reduce their density. During soaring, the body of the crustacean is located vertically or obliquely, with the anterior end of the body located higher than the posterior one. Having dropped a few centimeters down, the crustacean makes a sharp wave of all the pectoral legs and abdomen, and returns to its previous level, after which everything repeats again. Thus, the path of the crustacean in the water is drawn in a zigzag line. Some marine Calanoida, such as the near-surface species of the bright blue Pontellina mediterranea, jump so sharply that they jump out of the water and fly through the air like flying fish. If the pectoral legs act from time to time, then the posterior antennae, the palps of the mandibles and the anterior jaws vibrate continuously at a very high frequency, making up to 600-1000 beats every minute. Their swings cause powerful water cycles on each side of the body of the crustacean. 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 food, after which it enters the intestines.
The food of the filtering Calanoida is all organisms and their residues suspended in water. The crustaceans do not swallow only relatively large particles, repelling them with their mandibles. Planktonic algae consumed by crustaceans in large quantities should be considered the basis of Calanoida nutrition. Eurytemora hirundoides during the period of mass development of the Nitzschia closterium algae ate up to 120,000 individuals of these diatoms per day, and the food mass reached almost half the mass 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 intensity of Calanus filtration, algae labeled with radioactive isotopes of carbon and phosphorus were used. It turned out that one crustacean per day passes through its filtration apparatus up to 40 and even up to 70 cm3 of water, and it feeds mainly at night. Algae nutrition is essential for many Calanoida.
In addition to foltrators, there are also predatory species among Calanoida, most of which live at such ocean depths where planktonic algae cannot exist due to lack of light. The hind jaws and mandibles of such species are equipped with strong sharp spikes and devices for grasping prey. Particularly interesting are the adaptations for obtaining food in some deep-sea species. Winksted watched as the deep-sea Pareuchaeta hung motionless in the water, its elongated mandibles spread out to the sides, forming a kind of trap. As soon as the victim is between them, the jaws close, 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 for the active search for prey is not compensated by eating them.
The complex problem of their diurnal vertical migrations is related to the peculiarities of movement and feeding of Calanoida. It has long been noted that in all water bodies, both fresh and marine, huge masses of Galanoida (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 diurnal vertical migrations is different not only in different species, but even in one species in different places his habitat, different seasons years and at different age stages of the same species. Often nauplii and young copepodite stages always remain in the surface layer, while older copepodite stages and adult crustaceans migrate. The Far Eastern Metridia pacifica and M. ochotensis cover enormous distances every day. At the same time, other mass Far Eastern Calanoida - Calanus plumchrus, C. cristatus, Eucalanus bungii - migrate no more than 50-100 m. But in general, copepods show a preference for small migrations. It should not be thought that, while making vertical migrations, the weight of the crustaceans simultaneously moves in any particular direction. The English scientist Bainbridge went down under the water and made observations on migratory copepods. He saw how, in the same layer of water, part of the crustaceans moves up, and the other - down.
Not in all cases, vertical migrations can be directly related to the action of light. There are observations showing that crustaceans begin to descend long before sunrise. Esterl 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 surface layers rich in algae at night, the fish also cannot see them. These ideas cannot explain many well-known facts. For example, a number of copepods make regular short migrations without leaving the illuminated zone and, therefore, remaining accessible to planktivorous fish. The question of the causes of diurnal vertical migrations has not yet been finally clarified. At present, according to Yu. A. Rudyakov, all the proposed theories of the mechanism of migration can be divided into 3 main groups: 1) migration is a passive process caused by periodic changes in the rate of transfer of organisms by the vertical movement of water (in turn, associated with changes in temperature and water density or with internal waves); 2) migrations are carried out due to periodic changes in the rate of passive movement of animals relative to water (due, for example, to daily changes in the density of organisms due to the rhythm of feeding and digestion of food, etc.); 3) migrations are made due to the active movement of animals. In addition to daily vertical migrations, marine copepods also make seasonal migrations. In the Black Sea, the temperature of the surface layer rises, and Calanus helgolandicus, which lives there, drops to about 50 m, and returns to a shallower depth again in winter. In the Barents Sea, young stages of C. finmarchicus stay in the surface layers in spring and summer. After they grow up, in autumn and winter, the crustaceans descend, and before spring, individuals reaching sexual maturity begin to rise to the surface, where a new generation hatches. Especially numerous in the surface layers are crustaceans that are at IV-Y copepodite stages and are known under the name "red calanus", as they contain more quantity brownish-red fat. Red calanus is a favorite food of many fish, in particular herring. A similar nature of seasonal migrations, i.e., rising to the surface layers of water for reproduction, was found in many other mass species, for example, in Calanus glacialis, C. helgolandicus, Eucalanus bungii, etc. The females of these species need abundant nutrition of algae, and possibly in lighting. Other species (Calanus cristatuas, C. hyperboreus), on the contrary, breed 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 greater than daily migrations, and sometimes captures several thousand meters.
Representatives of the Calanoida suborder, currently numbering 1,700 species, are predominantly marine animals. Previous ideas about the wide distribution of many species of these crustaceans turned out to be wrong. Each part of the ocean is inhabited mainly by species unique to it. Each species of marine kalanids is settled due to the currents carrying crustaceans. Thus, the branches of the North Atlantic Current entering the Polar Basin carry kalanids there from Atlantic Ocean. In the northwestern part Pacific Ocean in the waters warm current One species lives in Kuroshio, and others 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 from the fauna of the Kalanid. The waters of temperate and tropical latitudes, and the tropical fauna is richer in species. Kalanid live at all ocean depths. Among them, surface species and deep-sea species are clearly distinguished, never rising into surface waters. Finally, there are species that make vertical migrations of a huge range, sometimes rising to the surface, sometimes descending to a depth of 2-3 km. M. E. Vinogradov called such species interzonal and emphasized their great role in the transfer of organic matter produced in the surface zone to the depths of the ocean. Some shallow-water species of kalanids in temperate waters develop in huge numbers and by weight make up the predominant part of the plankton. Many fish as well baleen whales feed mainly on calanids. These are, for example, herring, sardine, mackerel, anchovy, sprat and many others. In the stomach of one herring, 60,000 copepods swallowed by her were found. Of the whales, huge masses of kalanids are actively consumed by fin whales, sei whales, blue whales and humpback whales. Calanoida inland waters in their biology resemble sea views. They are also confined only to the water column, also make 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 middle parts of the USSR. Others are limited to 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. macrucus, which lives in the pre-estuary areas of northern rivers. The lakes inhabited by L. grimaldii were once covered by the cold Yoldian Sea. In Baikal, the crustacean Epischura haicalensis, peculiar only to this lake, lives in huge numbers, serving as the main food for omul. Some freshwater kalanids appear in water bodies only at certain times of the year, for example, in spring. In spring puddles, a relatively large (about 5 mm) Diaptomus amblyodon, painted in bright red or blue, often comes across. This species and some other widespread freshwater calanids are capable of laying dormant eggs that endure desiccation and freezing and are easily dispersed by wind over long distances.
SUBORDER HARPACTICIDA (HARPACTICOIDA) Representatives of the suborder Harpacticoida are mostly very small crustaceans with an elongated body of a more or less cylindrical shape, less often flattened. They are extremely diverse both in marine and in fresh waters, some species live in wet moss. Plant-mining species are known, such as Dacotylopusioides macrolabris, whose nauplii penetrate into the epidermis of brown and red algae, forming galls. Most harpacticids crawl along the bottom and benthic plants. Only a few species are able to swim for a long time and are part of the marine plankton (Microsetella). Much more characteristic are whole groups of genera and species of harpacticids that have adapted to living in special, unusual conditions, in particular in capillary passages between grains of sand on sea beaches and in underground fresh waters. Zoologists use a very simple technique to study the population of the capillary passages of sea sand. On the beach, above sea level, a hole is being dug. Water gradually accumulates in them, filling the capillaries of sand. This water is filtered through a planktonic net and in this way representatives of a peculiar fauna, called interstitial, are harvested. Harpacticids make up a significant part of this fauna and often show numbers that are 2 orders of magnitude greater than the abundance of representatives of macrobenthos. They are very widely distributed and found everywhere where relevant research has been carried out. The range of vertical distribution of marine harpacticides is also huge - from the littoral zone to a depth of 10002 m. last years a lot of new species have been described, but since the interstitial fauna has not yet been studied enough, experts believe that the number of harpacticid species currently known will undoubtedly increase several times in the near future. Most of the interstitial harpacticids belong to special genera that live only in such conditions, distinguished by an unusually thin and long body, which allows the crustaceans to move in narrow capillary passages. These species, like other representatives of the interstitial fauna, are characterized by small body size, high abundance, rapid reproduction rate, and unusually short life cycles. Fresh groundwater harpacticides are represented by a number of specialized genera - Parastenocaris, Elaphoidella, Ceuthonectes and others, partly very widespread, partly having narrow and broken ranges. For example, two species of the genus Geuthonectes live only in the caves of Transcaucasia, Yugoslavia, Romania, Italy and Southern France. These remote locations are considered to be the remains of a once much larger area of distribution of an ancient family. In some cases, a 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 surface waters, the latter (with a few exceptions) in groundwater. In all likelihood, the remains of an ancient tropical fauna that died on the surface of the earth under the influence of climate change. In tropical terrestrial waters, some harpacticides are adapted to living conditions reminiscent of living conditions in groundwater. known tropical species Elaphoidella living in peculiar micro-reservoirs formed in the leaf axils of aquatic plants from the Bromeliaceae family. The tropical Viguierella coeca lives under the same conditions, found on these plants in the botanical gardens of almost all countries. The peculiar fauna of Baikal is extremely rich in harpacticid species. 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 Baikal, on stones and aquatic plants, as well as on sponges growing here. Apparently, they feed on sponges and, in turn, become victims of the amphipod Brandtia parasitica, which also crawls on sponges. Some types of harpacticides are confined only to water bodies, very poor in salts, characterized by hyperacidity, i.e., associated with upland, sphagnum bogs. Among freshwater harpacticids, there are species capable of parthenogenetic breeding, which is not characteristic of all other copepods. In Elaphoidella bidens, which is widespread in Europe, males are generally unknown; under experimental conditions, this species was able to obtain 5 generations of parthenogenetic females. Epactophanes richardi was also capable of parthenogenetic reproduction, although under natural conditions it is represented by both females and males and reproduces by the usual sexual way. Apparently, some other types of harpacticids can reproduce parthenogenetically. The practical significance of the harpacticides is incomparably less than that of the Calanides and the Cyclopes. In some reservoirs, they make up a significant part of the food of fish, especially their juveniles.
Near-water birds are large and medium in size, but larger than large ones. The smallest representative of the detachment in our fauna - the small cormorant weighs about 800 g, the largest - pelicans - 10-13 kg. Outside of our fauna there are smaller copepods - phaetons, about the size of a crow or a seagull.
Copepods have a low landing on their legs (shin and tarsus are short) and a very characteristic structure of the paws: a well-developed swimming membrane connects all 4 fingers in them, and the back toe is turned somewhat forward and inward. The only exceptions are frigatebirds, in which the swimming membranes are strongly cut and do not reach the terminal phalanx of the fingers. Legs can be strong, strong, like those of pelicans, or, like frigatebirds, so weak that they can hardly 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 it is on land. Beaks of copepods are varied. They are either straight, almost conical, sharp, or slightly compressed from the sides, somewhat bent upwards, with a strong, bent down nail - the end of the beak, or, finally, wide, strongly flattened, with a strongly extensible, non-feathered skin throat pouch 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 frigatebirds it is forked with very elongated extreme tail feathers, and, finally, in phaetons it is long, stepped with elongated rudders of the middle pair.
The plumage of copepods is dense and (with the exception of pelicans) close to the body, rigid. Down grows on both pterylia and apteria; apteria are narrow. In those copepods that cannot dive, a very large pneumaticity of the skeleton is noted, air cavities are present in almost all bones. There is also a well-developed network of subcutaneous ramifications 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. The esophagus, glandular and muscular stomachs are highly extensible, which allows them to swallow big booty. Copepods are monogamous birds, settling 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.
Copepod nests are built in trees, bushes, rocks, reed beds or directly on the ground. The same nests are occupied for 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. Eggs in different species in a full clutch are from 1 to 5-6. 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. Dive (and sometimes even swim), some of them can not.
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 significance for fisheries, especially in inland waters and deltas big rivers has attracted the attention of many researchers. A number of species of copepods are undoubtedly of positive economic importance. Pelicans, cormorants and gannets, nesting on secluded and waterless islands in millions of pairs, leave in these places great amount litter, which accumulates over time in multi-meter layers. This is the famous guano, which for a number of decades served as the main nitrogenous fertilizer for marginal lands. 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 total nesting copepods is now estimated at about 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. The nesting sites of copepods were carefully guarded, and for visiting them at the forbidden time, the offender 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 plundering of natural reserves of guano began, accompanied by exceptional scale by the destruction of nesting colonies of guan-forming birds: tens of thousands of chicks were simply trampled under foot, eggs were broken, nests were torn down. Fleet 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 on guano, and at the beginning of our century it was found that nesting sites were cleaned, one might say, to the stone.
As a result of the measures taken in 1950, the islands already produced almost a quarter of a million tons of guano, not a single kilogram of which was exported. Thanks to this fertilizer, the lean soils of the Peruvian coast now yield over 320 kg of cotton per hectare, while, for example, Louisiana (USA) has a cotton yield of 55 kg per hectare, in the UAR - a little more than 70 kg per hectare. The order Copepoda 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), boobies (Sulidae), cormorants (Phalacrocoracidae) and frigatebirds (Fregatidae). It is possible that the darters, classified as cormorants as a subfamily, should, as some researchers do, be considered an independent family of Anhingidae. About 77 fossil species of copepods are known, one species (spectacled, or Steller, cormorant) has become extinct in historical time.
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 that studies copepods - copepodology (section of carcinology).
There is the World Society of Copepodologists. World Association of Copepodologists ), which publishes the newsletter " Monoculus copepod newsletter».
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Diversity of body shape of copepods (drawing by E. Haeckel) Dimensionsbody shape
Calanoid, fam. Diaptomidae Body sectionsThe body of copepods is divided into three tagmas: head - cephalosome (in copepodology it is sometimes called cephalothorax, cephalothorax), chest (thorax) and abdomen (abdomen). At the same time, many copepodologists call the telson (anal lobe) the last abdominal (anal) segment. The body of copepods can "fold" in half, curving in the sagittal plane. At the same time, the boundary between the functionally anterior part of the body (prosoma) and the functionally posterior part (urosoma) in cyclopoids and harpacticids passes between the segments of the thorax, which bear the fourth and fifth pairs of legs. These groups are united under the name "Podoplea" - "foot-belly". In kalanoids, the border between the prosoma and urosoma passes behind the segment bearing the fifth pair of legs, therefore they are called "Gymnoplea" - "blue-bellied". This character, which correlates well with other structural features, is given a high taxonomic weight, and Podoplea And Gymnoplea are considered as taxonomic categories (in modern classifications of copepods - as superorders). Head and its appendagesThe head bears the first one-branched antennae (antennales, mustaches), the second two-branched antennae (antennae), mandibles, first maxillae (maxillae), second maxillae (maxillae) and maxillipedes (mandibles) - 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, which carries swimming limbs, merges with the head, which can be greatly modified in this case. 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 front edge of the head there is a downward outgrowth - the rostrum, sometimes detached. Antennae I (antennales) are always single-branched. The number of their segments varies among representatives of different orders. So, harpacticids usually have 5-8 segments (up to 14 in males); most kalanoids have 21-27 segments; cyclopoids have 9 to 23 segments. In typical representatives, the relative length of the antennules differs: in kalanoids 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 carry sensilla. Antennae II are usually two-branched (in many cyclopoids they are single-branched), they are involved in creating water currents for swimming and feeding. The mandible is subdivided into a coxa, which forms a chewing outgrowth (gnathobase) with teeth and setae, and a palp, which initially consists of a basis, exo-, and endopod. Often the branches, and sometimes the base of the palp, are reduced. So, in many Cyclopes, only three setae extend from the mandible, which are considered to be the rudiment of the palp. On the chewing teeth of the mandibles of many marine copepods there are "crowns" made of silicon oxide, which help them to chew through the strong houses of diatoms. Breast and its appendagesOn the four segments of the chest following the mandibular segment, there are biramous swimming limbs - flattened legs that serve as the main engines when swimming, for the presence of which the detachment got 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 precox, which is weakly separated from the body). The outer (exopodite) and inner (endopodite) branches each consist of 2-4 segments and bear long setae covered with long thin outgrowths (setulae) and shorter spines. On the last segment of the chest is the fifth pair of pectoral legs, which usually do not participate in swimming and are greatly reduced or modified in many groups. In males of most families of kalanoids, they are sharply asymmetric. The endopodites of both legs are often rudimentary, the exopodite of one of the legs serves to transfer the spermatophore to the female's spermatheca during mating, and the larger exopodite of the other limb bears a long claw-like curved spine, which is involved in holding the female. The structure and armament of the fifth pair of legs for cyclopoids and kalanoids is the most important taxonomic feature. Abdomen and its appendagesThe abdomen usually consists of 2-4 segments (excluding the telson). On the first segment of the abdomen are paired genital openings. In harpacticids and cyclopoids, it has a rudimentary sixth pair of legs; in kalanoids, it is devoid of limbs. The remaining segments of the abdomen do not bear limbs. On the telson there are two movable appendages - a fork, or furka (furcal branches). These appendages consist of one segment and are not homologous to limbs. The furca bears furcal setae, the length and arrangement of which is an important taxonomic feature. sexual dimorphismTypically, in females, the first and second abdominal segments fuse to form a large genital segment; no such fusion occurs in males, so males have one more abdominal segment than females. Representatives 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. Many Calanoida females and males do not differ in size. Males have one modified antenna I, which is called the geniculate antenna. It is expanded in the middle part and is able to "fold in half"; like the Cyclopes, 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 structurecoversNervous system and sense organsThe central nervous system consists of the brain and the ventral nerve chain connected to it by the peripharyngeal nerve ring. An unpaired nerve departs from the brain to the naupliar eye and paired nerves to the frontal organ, as well as nerves to the antennules and antennae (the latter from the tritocerebrum). The subesophageal ganglion includes the ganglia of the mandibles, the first and second maxillae. The ganglia of the ventral nerve cord are slightly separated from each other. The entire abdominal nerve chain is located in the cephalothorax, it does not enter the abdomen. NutritionMost free-living copepods feed on single-celled or small colonial algae, which they filter out in the water column, as well as benthic diatoms, bacteria, and detritus, which they may pick up or scrape off at the bottom. Many species of kalanoid and cyclopoid are predators that eat other types of crustaceans (juvenile copepods and cladocerans), rotifers, insect larvae of I-II instars (including chironomid larvae and kulicid), etc. The copepodite stages of some freshwater cyclopoids climb into the brood chambers of Daphnia, where eggs are eaten. With more detailed study“filtrational” feeding of copepods with the help of high-speed microfilming revealed that many of them “hunt” for individual cells of algae, which they catch one by one. Algae-eating copepods store food energy in fat droplets found in their tissues, which are often yellowish-orange in color. In polar species, feeding primarily on diatoms, during the period of mass spring “blooming”, the volume of fat reserves can reach half of the body volume. Reproduction and developmentMating is preceded by complex sexual behavior, which, apparently, is usually played important role both chemoreception and mechanoreception. Female copepods secrete sex pheromones, which are perceived by males with the help of chemosensory bristles (aesthetics) of the first antennae. When mating in most Calanoid families, the male first captures the female by the telson or furcal branches with the help of a geniculating antenna, then by the body area located in front of or immediately after the genital segment with the help of the legs of the fifth pair, while the male and female are usually located "head to tail " each other . Mating lasts from several minutes to several days. Free-living copepods have spermatophoric fertilization. Large, comparable in size to the size of the animal's abdomen, kalanoid spermatophores are transferred to the genital segment of the female during mating with the help of the left fifth leg of the male; at its end there are "tweezers" that hold the bottle-shaped spermatophore by the narrowed basal part. Role in ecosystemsCopepods 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 the 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 cnidarians and ctenophores to baleen whales. surface water oceans are now considered the largest sink of carbon dioxide (2 billion tons per year - probably about a third of anthropogenic emissions). In many ways, the absorption of excess carbon dioxide is provided by the vital activity of copepods. Many planktonic copepods feed at night in the surface layers of the ocean, and migrate to the depths during the day to avoid being eaten by visual predators. Their corpses, discarded exuvia and fecal pellets sink into deeper layers of water. This (like the breathing of living copepods that digest food at depth) contributes to the movement of biogenic carbon from the upper layers of the water to the bottom sediments. In addition, the formation of fecal pellets during feeding of copepods contributes to the purification of the upper layers of water from mineral suspensions. This increases the transparency of the water and hence the production of phytoplankton.
"Salmon lice" ( Lepeophtheirus salmonis, neg. Siphonostomatoida) Role in human lifecopepod systemIn one of the recent reports on the taxonomy of crustaceans (Martin and Davis, 2001), it is proposed to consider copepods as a subclass, which is divided into two infraclasses and several orders:
In the proposed system, copepods are divided into 218 families. NotesLiterature
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Systematics
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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 that studies copepods - copepodology (section of carcinology).
There is the World Society of Copepodologists. World Association of Copepodologists), which publishes the newsletter " Monoculus copepod newsletter».
External structure
Diversity of body shape of copepods (drawing by E. Haeckel)
Dimensions
body shape
Calanoid, fam. Diaptomidae
Body sections
The body of copepods is divided into three tagmas: head - cephalosome (in copepodology it is sometimes called cephalothorax, cephalothorax), chest (thorax) and abdomen (abdomen). At the same time, many copepodologists call the telson (anal lobe) the last abdominal (anal) segment.
The body of copepods can "fold" in half, curving in the sagittal plane. At the same time, the boundary between the functionally anterior part of the body (prosoma) and the functionally posterior part (urosoma) in cyclopoids and harpacticids passes between the segments of the thorax, which bear the fourth and fifth pairs of legs. These groups are united under the name "Podoplea" - "foot-belly". In kalanoids, the border between the prosoma and urosoma passes behind the segment bearing the fifth pair of legs, therefore they are called "Gymnoplea" - "blue-bellied". This character, which correlates well with other structural features, is given a 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 the first one-branched antennae (antennales, mustaches), the second two-branched antennae (antennae), mandibles, first maxillae (maxillae), second maxillae (maxillae) and maxillipedes (mandibles) - 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, which carries swimming limbs, merges with the head, which can be greatly modified in this case.
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 front edge of the head there is a downward outgrowth - the rostrum, sometimes detached.
Antennae I (antennales) are always single-branched. The number of their segments varies among representatives of different orders. So, harpacticids usually have 5-8 segments (up to 14 in males); most kalanoids have 21-27 segments; cyclopoids have 9 to 23 segments. In typical representatives, the relative length of the antennules differs: in kalanoids 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 carry sensilla.
Antennae II are usually two-branched (in many cyclopoids they are single-branched), they are involved in creating water currents for swimming and feeding.
The mandible is subdivided into a coxa, which forms a chewing outgrowth (gnathobase) with teeth and setae, and a palp, which initially consists of a basis, exo-, and endopod. Often the branches, and sometimes the base of the palp, are reduced. So, in many Cyclopes, only three setae extend from the mandible, which are considered to be the rudiment of the palp.
On the chewing teeth of the mandibles of many marine copepods there are "crowns" made of silicon oxide, which help them to chew through the strong houses of diatoms.
Breast and its appendages
On the four segments of the chest following the mandibular segment, there are biramous swimming limbs - flattened legs that serve as the main engines when swimming, for the presence of which the detachment got 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 precox, which is weakly separated from the body). The outer (exopodite) and inner (endopodite) branches each consist of 2-4 segments and bear long setae covered with long thin outgrowths (setulae) and shorter spines.
On the last segment of the chest is the fifth pair of pectoral legs, which usually do not participate in swimming and are greatly reduced or modified in many groups. In males of most families of kalanoids, they are sharply asymmetric. The endopodites of both legs are often rudimentary, the exopodite of one of the legs serves to transfer the spermatophore to the female's spermatheca during mating, and the larger exopodite of the other limb bears a long claw-like curved spine, which is involved in holding the female. The structure and armament of the fifth pair of legs for cyclopoids and kalanoids is the most important taxonomic feature.
Abdomen and its appendages
The abdomen usually consists of 2-4 segments (excluding the telson). On the first segment of the abdomen are paired genital openings. In harpacticids and cyclopoids, it has a rudimentary sixth pair of legs; in kalanoids, it is devoid of limbs. The remaining segments of the abdomen do not bear limbs. On the telson there are two movable appendages - a fork, or furka (furcal branches). These appendages consist of one segment and are not homologous to limbs. The furca bears furcal setae, the length and arrangement of which is an important taxonomic feature.
sexual dimorphism
Typically, in females, the first and second abdominal segments fuse to form a large genital segment; no such fusion occurs in males, 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, which is called the geniculate antenna. It is expanded in the middle part and is able to "fold in half"; like the Cyclopes, 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
covers
Nervous system and sense organs
The central nervous system consists of the brain and the ventral nerve chain connected to it by the peripharyngeal nerve ring. An unpaired nerve departs from the brain to the naupliar eye and paired nerves to the frontal organ, as well as nerves to the antennules and antennae (the latter from the tritocerebrum). The subesophageal ganglion includes the ganglia of the mandibles, the first and second maxillae. The ganglia of the ventral nerve cord are slightly separated from each other. The entire abdominal nerve chain is located in the cephalothorax, it does not enter the abdomen.
Nutrition
Most free-living copepods feed on single-celled or small colonial algae, which they filter out in the water column, as well as benthic diatoms, bacteria, and detritus, which they may pick up or scrape off at the bottom. Many species of kalanoid and cyclopoid are predators that eat other types of crustaceans (juvenile copepods and cladocerans), rotifers, insect larvae of I-II instars (including chironomid larvae and kulicid), etc. The copepodite stages of some freshwater cyclopoids climb into the brood chambers of Daphnia, where eggs are eaten.
A more detailed study of the "filtration" feeding of copepods with the help of high-speed microfilming revealed that many of them "hunt" for individual cells of algae, which they catch one by one. Algae-eating copepods store food energy in fat droplets found in their tissues, which are often yellowish-orange in color. In polar species, feeding 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 both chemoreception and mechanoreception seem to usually play an important role. Female copepods secrete sex pheromones, which are perceived by males with the help of chemosensory bristles (aesthetics) of the first antennae.
When mating in most Calanoid families, the male first captures the female by the telson or furcal branches with the help of a geniculating antenna, then by the body area located in front of or immediately after the genital segment with the help of the legs of the fifth pair, while the male and female are usually located "head to tail " each other . Mating lasts from several minutes to several days.
Free-living copepods have spermatophoric fertilization. Large, comparable in size to the size of the animal's abdomen, kalanoid spermatophores are transferred to the genital segment of the female during mating with the help of the left fifth leg of the male; 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 the 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
Order: Cyclopoida Burmeister, 1834 = Copepods
Detachment of copepods - Cyclopoida - the largest number species are found in fresh waters.
Freshwater cyclops live in all kinds of bodies of water, from shallow puddles to large lakes, and are often found in very large numbers of specimens. The main zone of their habitat is the coastal strip with thickets of aquatic plants. At the same time, in many lakes, certain types of cyclops are confined to thickets of certain plants. So, for example, for Lake Valdai in the Ivanovo region, 6 groups of plants with their 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 to a considerable depth during the day.
Cyclopes swim a little differently than Calands. Simultaneously waving four pairs of pectoral legs (the fifth pair is reduced), the crustacean makes a sharp jump forward, up or sideways, and then, using the front antennae, can soar in the water for some time. Since the center of gravity of his body is shifted forward, while hovering, his front end tilts and the body can take 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 1/60th of a second.
Most Cyclopes are predators, but there are also herbivorous species among them. Such common, widespread species as Macrocyclops albidus, M. fuscus, Acanthocyclops viridis and many others swim quickly 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 spikes. The hind jaws and mandibles are involved in the transfer of food to the mandibles. The mandibles make quick cutting movements for 3-4 seconds, followed by a minute pause. Cyclops can eat oligochaetes and chironomids larger than themselves. The rate at which victims are eaten depends on their size and the hardness of their coverings. It takes 9 minutes to crush and swallow a 2 mm long bloodworm, and a 3 mm long larva is destroyed within half an hour. The more delicate, though longer (4 mm) oligochaete worm Nais 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 much the same way as predatory ones capture worms and bloodworms; in addition, various diatoms, peridiniums, 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 microns) and almost does not swallow small Chlamydomonas at all.
Freshwater cyclones are very widespread. Some species are found almost everywhere. This is facilitated primarily by adaptations to the transfer adverse conditions, in particular, the ability of crustaceans to endure the drying up of water bodies and passively spread 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 along with egg sacs, and forms something like a cocoon. In this form, crustaceans can be subjected to drying and freezing into ice without losing viability. In Kamerer's experiments, the cyclops were quickly eliminated by soaking dry sludge, which had been stored for about 3 years. Therefore, there is nothing surprising in the appearance of cyclops in spring puddles that occur when snow melts, in freshly flooded fish ponds, etc.
The second reason for the wide distribution of many species of cyclops should be considered the resistance of crustaceans, which are in an active state, in relation to the lack of oxygen in the water, its acidic reaction, and many other factors that are unfavorable for other freshwater animals. Cyclops strenuus can live for several days not only with total absence oxygen, but even in the presence of hydrogen sulfide. Some other species also tolerate adverse gas conditions well. Many cyclops exist excellently in water with an acidic reaction, with a high content of humic substances and extreme poverty of salts, for example, in reservoirs associated with upland (sphagnum) bogs.
Nevertheless, species and even genera of Cyclopes are known, limited in their distribution by some specific conditions, in particular temperature and salt conditions. So, for example, the genus Ochridocyclops lives only in Lake Ohrid in Yugoslavia, the genus Bryocyclops - in South-East Asia and in equatorial Africa. Close to the latter genus is the exclusively subterranean genus Speocyclops, species of which have been found in caves and groundwater in southern Europe, Transcaucasia, the Crimea, and Japan. These blind small crustaceans are considered to be the remains of a once more widespread heat-loving fauna.
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