Invertebrate Zoology: Textbook - T. A. Dauda 2014

Metazoa
Arthropoda
Subphylum Crustacea - Class Malacostraca - Order Copepoda

Copepods possess a slender, elongated body typically measuring about 1–2 mm in length, and rarely up to 10 mm. They lack a carapace. A single eye is located on the HEAD, which gives rise to their name—cyclopes (the one-eyed creatures of Greek mythology). Their antennules are highly developed; in many species, these are fringed with setae and function as oars or as a mechanism for suspension. The thoracic appendages are biramous, covered with setae, and used exclusively for swimming. Copepods respire through their entire body surface. The legless abdomen terminates in a caudal furca. Females carry fertilized eggs in egg sacs attached to the abdomen near the genital opening.

Typical representatives include cyclopoids (see Fig. 49) and diaptomids. They abundantly inhabit rivers, ponds, and lakes, where they constitute a significant component of the diet of fry and planktivorous fish. Nevertheless, cladocerans remain the primary food source for fish in freshwater bodies, whereas copepods dominate in marine environments. Marine plankton is typically characterized by calanoid copepods, which frequently (especially in northern seas) appear in such massive numbers that the Water over large areas turns reddish. It is precisely in these locations that many species of marine fish and whales find their food supply.

Cyclopes and diaptomids serve as intermediate hosts for certain parasitic tapeworms (such as the broad fish tapeworm and the common ligulid tapeworm).