Copepods - Characteristics Of Free-living Copepods, The Parasites, Place In The Food Chain, Order Calanoida
phylum species containing photo
Copepods are pale or translucent crustaceans, measuring between 0.04 mm to several millimeters long. They have adapted to many different habitats; while they usually live in salt water, copepods can live in lakes and ponds as well. Furthermore, they have different modes of locomotion: some can swim purposefully but others are planktonic, floating with the current. Scientists generally
A copepod (Diaptomus sp.). © M.I. Walker/Science Photo Library, National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.
distinguish between two basic forms of copepods, free-living and parasitic.
The phylum Arthropoda is the largest phylum in the animal kingdom, containing more than one million species. Within this phylum, the subphylum Crustacea contains some 35,000 species and can be broken down into eight classes. Copepods belong to the class Maxillopoda and the subclass Copepoda, containing seven orders and more than 7,500 species. Three of these orders—Calanoida, Cyclopoida, and Harpacticoida—are primarily free-living and are present in huge numbers. The other orders are: Misophrioida, Monstrilloida, Siphonostomatoida, and Poecilostomatoida.
Additional Topics
Given the incredible number of species, the physical structure of copepods varies greatly. However, the free-living forms of copepods have certain physical traits in common. For instance, the body is usually short and cylindrical, composed of a head, thorax, and abdomen. The lower part of the copepod's head is generally fused with its thorax; the front of its head often juts forward, like a…
There are over 1,000 species of parasitic copepods. As larva—or nauplia—most look and act like typical copepods. It is only later, when the parasites reach various stages in their development, that they begin to attach themselves to a host creature and radically change in appearance. In fact, many of the adult parasitic copepods are incredibly deviant in physical structure from their…
Calanoids are of major importance to the commercial fishing industry. Like other copepods, this species filters minute animal algae from the water and eats it in large clumps. In turn, these copepods are eaten in large numbers by fish, such as herring and salmon. Calanoids thrive close to the surface of large expanses of water, both seas and lakes. Anatomically, they are easy to recognize. The fus…
All of the free-living cyclopoida are almost identical to each other in physical appearance. Their antennae are shorter than those of the calanoids, growing about half of the length of their bodies. Their bodies, relatively pair-shaped, have two clearly divided regions: the head and thorax in the front; and the last segment of the thorax fused with the abdomen in the rear. Their front portions nar…
Some of the most advanced species of parasitic copepods are found in this order. These copepods are worm parasites. Their nauplii appear quite typical, but have no stomach. When they find a suitable host, they shed their outer skeleton and all of their appendages and become a mass of cells. In this simple structure, they are able to reach the worms' body cavity. Once inside their host, thes…
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