INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 2 - H.I. Shcherbak - 1996

PHYLUM ARTHROPODA (ARTHROFODA)

SUBPHYLUM BRANCHIATA, OR CRUSTACEA

CLASS MAXILLOPODA (MAXILІOPODA)

SUBCLASS COPEPODA

Copepods inhabit all types of fresh and marine waters. In terms of feeding habits, they can be filter feeders, predators, or herbivores; there are planktonic forms as well as benthic inhabitants, etc. Nearly 9,000 species have been described. Over 20% of them lead a parasitic lifestyle.

The body ranges in length from 0.1 to 32 mm, consisting of a syncaphalon, a five-segmented Thorax, and a three- to four-segmented abdomen ending in a telson with a furca (Fig. 78). A naupliar eye is present on the HEAD. The antennules are elongated, sometimes longer than the body, and perform swimming and sensory Functions (chemosensory, tactile); they are uniramous. The antennae are shortened, typically biramous. The mandibles bear masticatory Teeth. In some marine species, these teeth are covered on top with silicon dioxide crowns, which increases their strength. There are two pairs of maxillae and a pair of maxillipeds. In filter-feeding forms, the antennae and jaws generate Water currents and function as a filtering apparatus. The five pairs of thoracic legs are biramous and swimming; in males of certain species, the last pair is modified to attach spermatophores to the female genital openings (which are located on the I abdominal segment in both sexes). The furca often consists of several branches and is covered with long setae, which improves suspension in the water. The Respiratory system is absent; a Heart is present only in certain representatives (suborder Calanoida) in the form of a small vesicle.

In parasitic species, the head appendages are transformed into Organs of attachment to the host, taking the form of hooks, etc.; the thoracic legs partially or completely disappear, the integument becomes soft, Sensory Organs are reduced, and segmentation becomes indistinct or disappears entirely.

Copepods are dioecious. There is quite significant Sexual Dimorphism: males are smaller than females, and there are differences in The Structure of the antennules and posterior thoracic legs; the two sexes differ particularly sharply in parasitic species. Parthenogenesis is known in some freshwater forms. Fertilization is spermatophoric.

Some primitive planktonic species release their eggs directly into the water, whereas some free-living forms (such as Cyclops) and parasitic crustaceans form one or two egg sacs attached to the Base of the female's abdomen—a distinctive form of parental care. The nauplius goes through 5–6 stages, after which it transforms into the so-called copepodid larva, in which the abdomen is segmented and the thoracic legs gradually form; it also passes through 5–6 stages. In deep-sea and cave-dwelling copepods of small size (up to 1 mm), the number of larval stages decreases, and fecundity drops to 1–2 eggs per clutch.

From three to eight orders are distinguished within the subclass Copepoda. We will examine only some of them and the parasitic species belonging to various orders.

Representatives of the order Calanoida are exclusively planktonic forms. They are well adapted to this lifestyle: very long branched antennules (Fig. 78, a), elongated and broad head and thorax, shortened abdomen (adaptations for suspension); they maintain a vertical position in the water. They inhabit various depths, predominantly in marine waters; their feeding habit is primarily filtration, although predators also exist. Calanoids are the foundation of marine plankton, forming the largest animal biomass on our planet.

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Fig. 78. Copepods:

a - Oithona plumifera; b - Cyclops strenuus; 1 - antennule; 2 - antenna; 3 - naupliar eye; 4 - syncaphalon; 5 - egg sacs; 6 - furca

In the surface layers of the Black Sea, *Calanus helgolandicus* is widespread, colored red—especially in its copepodid stages—due to the presence of specific Lipids ("red calanus"); it serves as The basis of Nutrition for various marine Fishes, particularly herrings. In addition to fish, baleen whales also feed on calanoids. The nutritional properties of these crustaceans are very high: they contain up to 60% protein, 20% CARBOHYDRATES, and 15% fats.

Species of the order Cyclopoida mainly inhabit the bottom or benthic zone. Their head, thorax, and antennules are shorter, and their abdomen is longer, than those of calanoids; females always have two egg sacs (Fig. 78, b). For the most part, these are highly abundant inhabitants of freshwater bodies. They move in a jumping manner, simultaneously striking with four pairs of thoracic legs (the fifth pair is reduced). Most are predators, feeding on Protozoans, small oligochaetes, aquatic insect larvae, other crustaceans, fish larvae, etc.; There are also herbivores that consume primarily unicellular or colonial green, diatom, and blue-green Algae. Some lead a planktonic lifestyle (*Cyclops strenuus*); there are numerous parasites. Cyclopoids and their nauplii form the basis of the diet for the fry of most freshwater fishes. On the other hand, parasitic species harm fish, and some serve as intermediate hosts for tapeworms.

The order Harpacticoida includes very small crustaceans; their body (Fig. 79) is typically elongated and narrow, with shortened antennules, which is attributed to their benthic lifestyle; many species inhabit interstitial environments, such as between sand grains on the bottom. They populate marine and freshwater bodies; some live on land, in well-moistened growths of mosses and Lichens. The vermiform shape is caused by the fact that they crawl using their thoracic legs while bending the body. The species *Elaphoidella bidens* is very common in freshwater bodies.

Fig. 79. *Microsetella spinicauda*

Among them, There are many parasitic species: both ecto- and endoparasites of various marine invertebrates—Cnidarians, echiurans, polychaetes, Mollusks, Echinoderms, etc.

On fish and whales, they settle mainly on the integument, gills, and sometimes in the Oral Cavity. Species of the genus *Ergasilus* (Fig. 80, a) inhabit the gills of freshwater fish; sometimes several thousand parasites attach to a single host, leading to the death of the fish. Larvae and young individuals lead a free-living lifestyle, and only after copulation do the crustaceans

attach to the gills. Crustaceans of the genus *Mytilicola*, which are parasites of mussels, cause great damage. In some years, mussel stocks decrease tenfold due to these parasites. The largest representative of copepods, *Pennella balaenopterae*, parasitizes the Skin of whales and reaches a length of 32 mm. Interestingly, a copepodid larva hatches from the egg in *Pennella*; development involves a change of host—young individuals parasitize cephalopods after copulation and then transfer to whales. Parasitic copepods cause severe damage to freshwater and certain marine fishes, posing a particular hazard to fry in fish-farming enterprises.