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Calanoid copepod

Calanoid copepod

The Copepoda is a huge group worlwide, with well over 4500 species described. Most are marine and some are parasitic on fish. They are economically very important as they are a major food source for fish.

Harpacticoid copepod

Harpacticoid copepod

The largest will be a few millimeters in length and most will be less than a millimeter. They vary but typically they have a short and cylindrical body of head and thoracic with tapering abdominal segments. They have a median, basic eye. The first pair of antennae are usually long. The second pair of antennae are shorter. There are several groups of copepods: the large calanoids, harpacticoids and cyclopoids. The later are often associated with freshwater. Harpacticoids may be found nearer the bottom whilst the calanoid types are open water.

Swimming is through the use of thoracic appendages and the respiratory current they produce. The antennae are used to stabilize them in the water and help prevent sinking. Harpacticoids have smaller antennae as they do not need the buoyancy and some live amongst sand grains. They are filter feeders and most feed on phytoplankton. The mouthparts can beat up to 2500 times a minute and this produces a swirling action down the body which in turns moves the body through the water. Some copepods, particularly the larger ones are omnivorous, e.g. Harpacticoids, whilst others are strictly meat eaters, e.g. Cyclops .

After mating the female carries a sac (or two) at the end of the abdomen with the eggs. On hatching these become nauplii larvae. After five or six moult stages they become a young adult copepod. A further five or six moults and they are fully grown. This can take a week or much much longer.

Also see copepod nauplius larva.

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