Copepods. Detachment Copepods, or Pelicans - Pelecaniformes. Nervous system and sense organs

Free-living copepods have certain signs of adaptation to life in the water. So, devices for “soaring” in the water column are small body sizes (0.1-3 mm), due to which the relative surface area of ​​​​the body increases, the presence of various outgrowths to increase friction against the water (antennae, furks, antennular outgrowths), thin covers body, storing fat in reserve in cells, which leads to a decrease in body density. This allows copepods to stay in the water column for a long time with little energy consumption. These organisms are characterized by bioluminescence, and representatives of many families of copepods glow in the dark due to the release of a luminous secret. Most free-floating copepods feed on unicellular algae, absorbing them through filtration, and detritus, bottom bacteria also serve as their food. Rare species some subgroups of copepods are predators. They eat insect larvae, other small crustaceans, their eggs.

External structure

In the body, a head, a chest, often merging into a cephalothorax, and an abdomen are distinguished. Two pairs of antennae are located on the head: the first are single-branched, the second are two-branched. oral apparatus It is a mouth opening covered by the upper and lower lips, and oral appendages (maxillas, mandibles). There are mandibles - appendages of the first thoracic segment, firmly fused with the head. The swimming limbs are attached to the second thoracic segment, which in some species is also firmly fused with the head, they are highly modified in different species.

After the mandibular segment, there are four segments of the chest, from which two-branched flattened swimming limbs extend, which are the main elements in swimming. This feature of the structure was the reason for the name of the detachment "copepods".

In the structure of the abdomen, 2-4 segments are distinguished. hallmark females - fusion of the first and second segments of the abdomen with the formation of a large genital segment. The first segment has paired genital openings.

Internal structure

Nervous system represented by the brain, parapharyngeal nerve ring and abdominal nerve cord (within the cephalothorax). Digestive system consists of the esophagus, anterior and posterior intestine, ending in the anus at the posterior edge of the abdomen. Copepods have a heart but no blood vessels. The hemolymph enters directly into the body cavity and moves there due to bowel movements. Breathing is carried out by the entire surface of the body.

The vast majority of copepods are dioecious animals. Characterized by sexual dimorphism. Some time after mating, the female lays eggs. The hatched larvae after several molts turn into adult crustaceans.

The value of the copepods. These crustaceans play an important role in food chains. Due to the largest biomass, copepods are the main consumers - consumers of phytoplankton. In turn, copepods are the main part of the diet of many aquatic animals - from hydroids to big fish and whales. Thanks to the vital activity of these crustaceans, the upper layers of water bodies are cleared of mineral suspensions, thereby increasing the transparency of water bodies and, as a result, increased development of phytoplankton. It is important that the absorption of excess anthropogenic carbon dioxide occurs precisely by phytoplankton, which is interconnected with the vital activity of copepods.

Characteristics of the detachment Copepods -Copepoda

The body of free-living copepods is divided into cephalothorax, thorax, and abdomen. The head is fused, without any traces of segmentation, fuses with the first thoracic segment, forming the cephalothorax. The front end of the head is often extended into a beak curved down, or rostrum. The absence of paired compound eyes is very characteristic; only the naupliar 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 the sense organs: sensitive bristles and cylindrical sensitive appendages sit on them. The posterior antennae are short, usually biramous. Mandibles are powerful and have a two-branched palp. Their chewing, highly chitinized part has sharp teeth that help break up food. A close examination of the teeth of the chewers of some marine copepods revealed that these teeth are covered with flint crowns, which increase their strength. The opening of flint crowns is interesting in two respects. First, it indicates the ability of copepods to absorb and concentrate silicon; almost all higher invertebrates - worms, molluscs, and other arthropods - are deprived of such an ability. Secondly, one can hope to find flint crowns of ancient copepods in geological deposits, almost completely not preserved in a fossil state.

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

The posterior antennae, mandible palps, and forelimbs of filtering copepods make frequent and continuous strokes, creating water cycles that bring suspended food particles. These particles are filtered out mainly by the setae of the hind jaws.

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 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 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 are adapted for soaring in water, as they prevent the crustacean from sinking.

Respiration of copepods is carried out by the entire surface of the body, there are no gills. Possibly, the weak development or even the absence of circulatory system. Only representatives of the suborder Calanoida have a heart, and even they have a small one, although it beats very often: for example, in the marine crustacean Labidocera, it makes more than 150 beats per minute. In other copepods, the abdominal fluid is set in motion by contractions of the intestine.

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 tweezers that capture the spermatophore and transfer it to Right place. From the spermatophore, the sperm enters the female's seminal receptacle. When eggs are laid, they are fertilized.

In some copepods, one is formed in this way, in others - two egg sacs, which the female wears on herself until the larvae leave the eggs.

A larva emerges from an egg nauplius. The larva molts many times and gradually approaches in its characteristics to 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 antennas 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 pectoral legs. Different copepods require different times to complete metamorphosis, and the biology of larvae is far from being the same for all species.

The way of life, way of feeding 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.

Free-living copepods belong to the suborders Calanoida, Cyclopoida, and Harpacticoida. Representatives of all three suborders inhabit both the seas and fresh waters.

All V. are separate sexes; males usually differ from females in the structure of the front antennae, which serve them for grasping and holding females during copulation. The fifth pair of swimming legs also serves as an auxiliary organ during fertilization, specifically for gluing spermatophores, and then has a different shape than in females. The reproductive organs, both male and female, usually consist of an unpaired gland located in the cephalothorax, above the stomach, and for the most part of two more or less long and tortuous excretory canals that open outwards on the first abdominal segment. Spermatozoa come out in special capsules (spermatophores), which the male sticks to the so-called with the help of the hind legs. genital segment of females, sticking them into the genital openings or into the openings of special seed receivers (receptaculum seminis). The eggs are fertilized by spermatozoa as they are released. In the last part of the oviduct, a light and viscous mass hardens in water, which envelops the eggs that come out and sticks them together. Thus, two sacs with eggs are formed, attached to the right and left sides of the abdomen, which the female constantly carries with her (Fig. 1, Fig. 4 b); sometimes one unpaired pouch is formed. Inside these sacs, sticking out in the genital openings, the development of eggs takes place, and only with the release of the embryos are the sacs themselves destroyed. Development is accompanied by a rather complex and in many V. regressive metamorphosis. The embryos come out in the form of that larvae, typical of lower crustaceans, which is called the nauplius (see this next); they have an oval body with a small unpaired ocellus and three pairs of limbs, of which both posterior pairs terminate in two branches (Fig. 2).

I. Free-living V., to which, in fact, the previous description refers, with mouthparts that serve for chewing food, belong to the number of very ordinary animals. About 60 freshwater species are known in Europe; they are found in shallow still or slowly flowing waters, sometimes in huge number, and constitute the main food of some fish. Among the free-living marine copepods, some stick to the coast, others live on the high seas; marine waters are sometimes found in innumerable masses, which, for a long distance, give the surface of the sea red or yellow and serve as food for fish, for example. for herring and mackerel. The food of free V. is made up of small living animals. They are divided into 6 families containing about 500 species. Most freshwater V. belongs to the family Cyclopidae, To various types the genus Cyclops; cyclops are up to 3 mm long (males are smaller), greenish, brown, and other colors (Fig. 1).

From the family Calanidae a species of Cetochilus septentrionalis, in European seas, often colors the sea reddish. Diaptomus castor - in fresh waters.

B. The second suborder, the tail-gills (Branchiura), differs in many respects from true copepods and contains only one family of karpoeds, Argulidae. Common carp (Fig. 6) (Argulus foliaceus) greenish in color, 5-6 mm long, lives on the skin of carps and other freshwater fish, sucking blood out of them; during the breeding season, karpoeds leave their host and swim freely.

1. Cyclops Cyclops coronatus, female, from the dorsal side: A′, A″ - first and second pair of antennae, In - intestines, Ov - egg sacs. 2. Cyclops larva in the Nauplius stage: A′, A″ - first and second pair of antennae, M - third pair of legs of the larva, future mandibles. 3. Perch eater Ac htheres percarum: a - nauplioid larva, b - female from the ventral side, c - male from the side, Mxf′, Mxf″ - first and second pair of jaw legs, In - intestines, Ov - ovaries, Kd - glands that secrete sticky liquid. 4. Chondracanthus gibbosus: a - female from the side, b - female from the ventral side, c - male from the side, An′ - first pair of antennae, An″ - second pair, turned into hooks. F′, F″ - legs, A - eye, M - oral parts, Oe - esophagus, In - intestines, T - testes, Vd - their excretory duct, Sp - sac with spermatophores, Ov - egg sacs, ♀ - male, attached to the body of the female. 5. Lernaea branchialis: a - male (2-3 mm long), b - female (during the fertilization period, 5-6 mm long), c - female after fertilization, d - the same with egg cords, in nature. size, Oc - eyes, M - stomach, T - testicles, F′ - Fiv - swimming legs, Sp - bags with spermatophores, A′, A″ - 1st and 2nd pair of antennae, R - proboscis, Mxf - jaw legs. 6. Argulus foliaceus, male.

And interstitial fauna are less common in plankton. The structure and lifestyle of free-living representatives of copepods are mainly considered below.

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

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  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. In this case, 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 of a large upper lip, and behind - 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. At 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.

  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 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 unicellular 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 age (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. At polar species, feeding primarily on diatoms, during the period of mass spring “blooming”, the volume of fat reserves can reach half the volume of the body.

  Reproduction and development

  Mating 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 geniculate 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 the proportion of secondary products reservoirs. 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.

  
  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. In this case, 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 unicellular 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 age (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 geniculate 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