Types of Copepods
Copepods are small marine and freshwater crustaceans that make up the one of the largest groups of animals in the animal kingdom. There are close to 7500 separate species of copepod, with about 2000 of them being parasitic in nature.
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Features
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Unlike most crustaceans, copepods do not have a hard shell covering the front parts of their bodies, and they only have one eye located in the center of their head region, which are never on stalks as with most other crustaceans.
Types
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Copepods are divided into groups based on living arrangements. There are four distinct types of free floating and several more parasitic. The copepods that parasitize fish are usually external parasites and are well adapted to living the life of a parasite. The four groups of free floating copepods are the Calanoida, the Cyclopoida, the Harpacticoida and the Misophrioida, with the last group being the most rare.
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Calanoids
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Out of all the copepod species, the Calanoida are the largest, with an average body size of approximately a grain of rice. They sport a rather large first antenna and their body segments are adorned with bristles and other structures designed to keep them afloat by providing resistance against the water. Calanoids are important to the food chain as they make up the majority of all marine food chains.
Cyclopoids
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Cyclopoids are somewhat rare and indistinguishable from each other. Cyclopoids are normally found in freshwater systems, while the others tend to be found in marine or brackish environments. These copepods lack a rostrum or small pointed projection on the front end of the organism, which are common in other species. Cyclpoids are planktonic, living along the surface of the water.
Harpacticoids
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Harpacticoids generally live along the bottom of the ocean or swim just above the bottom. They provide a food source for coral, small fish and sea anemones. In reef tanks, these are normally the first "bugs" to be seen colonizing the walls shortly after setup. The life cycle of the herpacticoid is short, lasting only a few days between hatching and dying. While most are found free-living along the bottom, some have been known to parasitize coral.
Considerations
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Copepods are common organisms that play a pivotal role in the ecology, providing a food source to many aquatic species of animals. Their contribution to the nutrient flux is of great importance and should not be overlooked both in the wild and in our aquariums.
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