Descriptive Features: free living forms: small, elongate cylindrical body
anterior portion of body (metasome) broader than posterior portion (urosome)
well defined head, fused posteriorly to thoracic segments 1 or 2 to form cephalic segment (cephalothorax)
single eye anteriorly
6 thoracic segments
2 - 5 abdominal segments
paired appendages on head, conspicuous antennules, smaller antennae, mandibles, maxillules and maxillae
pair of maxillipeds on 1st free thoracic segment, a pair of well developed swimming legs on each successive segment, modified pair of legs on last segment
last abdominal segment terminates in caudal rami
Total length: up to 4 mm
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Copepod-nauplius |
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Ecology: Instream habitat: Copepoda are planktonic. Two orders, Caligoida and Lernaeopodida, are parasitic upon fish whilst the other three orders, Calanoida, Cyclopoida and Harpacticoida, are free living and consequently most likely to be collected. Calanoida are found in limnetic areas of fresh and saline standing waters. Cyclopoida occur in littoral areas of lakes, ponds, ditches and slow flowing areas of streams. Some species are endemic. Harpacticoida are rare and found living on macrophytes and in benthic sediments.
Feeding ecology: Juvenile copepods (nauplii or copepodites) are a major part of the diet of young fish. Free living copepods are regarded as omnivorous, feeding on phytoplankton as well as nauplii, rotifers and small cladocerans.
Habit: Free living copepods are active swimmers, beating the first antennae in a rowing action to propel themselves through the water.
Life history: Male copepods clasp females with their first antennae during mating. Eggs are held for a short time in one or two egg sacs attached to the anterior part of the urosome. They hatch to nauplius larva. This is small, unsegmented and ovoid with three pairs of appendages; antennules, antennae and mandibles. There are six naupliiar instars followed by five copepodid stages before the adult form is attained. The copepodid stage is small, adult like but without the full number of biramous swimming legs. Sexes are separate with sexual dimorphism reached during the final moult from copepodid stage five to six. Copepods reach peak reproductive maturity at twenty four days with a life span of fifty days. Populations of copepods are influenced by temperature, food availability, predation and overcrowding.
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