Characteristics of Copepods

Size

• The copepod Pennella balaenopterae grows to a respectable size. Its maximum length is about 32 centimeters. But practically all the others are only a few millimeters long. Some are even less than one-half millimeter, according to the Encyclopaedia Britannica.

Segmented Body

• The copepod body consists of a head, a middle section called a thorax, and the terminal section called the abdomen. The abdomen consists of four or five discrete segments, depending on the species. The thorax contains six segments. The unsegmented head is integrally united with the first segment of the thorax, according to Animal Life Resource.

Characteristics of Antennules

• The copepod head has a pair of segmented antennules (little antennae). The segments at the end of each antennule have bristle-like structures called setae and thin-walled hairs called aesthetascs. The aethetascs of the male copepod have receptors that can sense chemical substances emitted by female copepods. The male has longer antennules which develop a joint that enables it to grasp the female during copulation, according to the Royal Society of Biological Sciences.

Eyes and Mouth

• Some copepods have only one eye. The copepod’s mouthparts are complex and vary from species to species. Sometimes the mouthparts of the male and the female differ. But the mouthparts or species of the genus Boeckelia have characteristics shared by many copepods. They possess three pairs of mouth parts. Two pairs are called maxillae and the other is a pair of mandibles. The setae of the antennae assist in directing food to the mouth, and a pair of maxillipeds on the first thoracic segment also assist in feeding, according to Taylor &Francis.

Appendages

• Each segments of the copepod thorax has a pair of appendages, but the abdomen has none. The last segment of the abdomen terminates in a sort of tail called a “caudal rami,” according to Lusce’s Web Portal.

Modes of Existence

• Some copepods are able to swim, using their thoracic appendages as oars. The antennules also help in swimming. Other copepods float about like plankton. Many live as parasites on fish or on animals that become infected when they drink water. For example, Lepeophtheirus salmonis, the salmon louse and parasitizes salmon, according to Animal Life Resource.

Life Cycle

• The fertilized eggs stick to the abdomen of the female until they hatch. The newly-hatched copepod is a larval form called a ”nauplius.” The nauplius differs from the adult in appearance and possesses a yoke sac from which it receives nourishment until sufficiently developed to obtain its own food, either by parasitism or by feeding on plankton, depending on the species. After the nauplius stage, the copepod exists in five more larval stages before it becomes an adult. A male and female adult then mate and begin a new life cycle.