INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM METAZOA

SUBKINGDOM EUMETAZOA

SECTION TRIPLOBLASTICA, OR BILATERIA

SUBSECTION ECDYSOZOA

PHYLUM ARTHROPODA

SUBPHYLUM BRANCHIATA, OR CRUSTACEA

CLASS MAXILLOPODA

SUBCLASS COPEPODA

Copepods inhabit all types of fresh and marine waters, including both planktonic and benthic species. Their feeding strategies include suspension feeding, predation, and herbivory. Approximately 11,500 species have been described, with over 20% leading a parasitic lifestyle.

Body length ranges from 0.1 to 32 mm. The HEAD bears a naupliar eye. The long antennules function in swimming and sensation. The antennae are shortened. The mandibles feature biting Teeth, capped in some marine species by silica crowns that increase their durability. The five pairs of thoracic limbs are biramous and swimming-oriented, with oar-like movements,

hence the name of the subclass. The furca often consists of several branches covered with long setae, which enhances gliding in Water (Fig. 330). In parasitic species, head appendages transform into attachment Organs for clinging to the host, appearing as hooks or similar structures; thoracic limbs are partially or completely reduced, integuments become soft, Sensory Organs regress, and segmentation becomes indistinct or completely absent (Fig. 331).

Copepods are dioecious; Sexual Dimorphism is quite pronounced, with sexes differing especially drastically in parasitic species. Parthenogenesis is known in some freshwater forms.

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Fig. 330. Cyclops Cyclops strenuus

(from Dogel): 1 - antennule; 2 - antenna; 3 - naupliar eye; 4 - syncephalon; 5 - egg sacs; 6 - furca

Fertilization is spermatophoric. Development proceeds with metamorphosis; the larvae include the nauplius, metanauplius, and additional stages—copepodid larvae—which transform into adults after five molts.

In marine plankton, species of the order Calanoida are the most abundant, making up the largest animal biomass on our planet. Calanoids play a vital role in food webs: they are filter feeders that serve as prey for numerous fish species and baleen whales. The red-pigmented *Calanus helgolandicus* is widespread in the Black Sea, particularly its copepodid stages, due to the presence of specific Lipids ("red calanus").

In freshwaters, Representatives of the order Cyclopoida reach high population densities. Most species inhabit the bottom or benthic zone of freshwater bodies, while some lead a planktonic lifestyle (*Cyclops strenuus*) (Fig. 330). They are predominantly predatory, though herbivorous forms also exist, feeding mainly on unicellular Algae. Among copepods, there are numerous parasitic species, including both ecto- and endoparasites of various aquatic animals. On fish and whales, they typically attach to the integument, gills, and occasionally the Oral Cavity.

Species of the genus *Ergasilus* (Fig. 331) parasitize the gills of freshwater fish; sometimes several thousand individuals can be found on a single host, causing the fish's death.

Fig. 331. Females of parasitic Copepoda from freshwater fish (from Markevych):

a - Ergasilus peregrinus, b - Achteres

The order Harpacticoida comprises very small crustaceans with a narrow, elongated body (Fig. 332). Most of them have adapted to life in capillary spaces between sand grains on marine beaches and in subterranean freshwaters (interstitial fauna). Some species inhabit bogs and well-moistened moss and lichen mats.

Fig. 332. Harpacticoid Arenosetella spinicauda (from Birshtein)