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Phylum Arthropoda
Subphylum Crustacea
Class Maxillopoda
Subclass Copepoda


  • Most are between 1 and 5 mm long, though a few reach 10 mm.

Distinguishing characteristics

  • Copepods have short cylindrical bodies clearly divided into a number of segments. The head section is usually rounded and bears prominent, often very long antennae, which when held away from the body, serve to slow sinking rate. There are usually 9 free trunk segments. The anterior segments bear the swimming appendages while the posterior segments taper, ending in a pair of caudal rami at the base of the abdomen.
  • Identification of adults to species level can be difficult (particularly so for early developmental stages).
  • Taxonomic features that are important are the degree of segmentation of the endopods of the pereiopods, presence of lenses on the cephalosome and spines on the metasome and number of setae on the caudal rami.
  • Many of these features vary with sex.
  • Males can usually be distinguished by being slightly smaller than females, and by having modified antennules (1st antennae) which are used to grasp the female during mating. The 5th pereiopods are sometimes greatly modified for transfer of sperm packets (spermatophores) during mating.
  • Mature females can be distinguished by a swollen genital segment (1st urosomal segment).


  • Copepods are probably the most common and abundant holoplanktonic organisms worldwide, occurring in all oceans, seas, estuaries, rivers and lakes.
  • Previous studies have found around 50 different species in coastal waters off Tasmania’s east coast.


  • Copepods are the most important herbivores in the sea, filtering phytoplankton using a sophisticated ‘fling and clap’ technique to grasp the tiny plants while squeezing the water through fine meshes on the limbs.
  • Some species are modified as carnivores and eat other copepods using limbs armed with sharp spines.
  • Identification of copepods to species can be quite difficult and may require delicate dissection with fine instruments to remove limbs that are then mounted on a glass slide so that they can be observed under high magnification.
  • All copepods have a complex life history.
  • Eggs are sometimes carried in sacs attached to the thorax until ready to hatch, or are released freely into the water once fertilised.
  • The larval phase consists of 6 naupliar stages and 5 copepodid stages before the adult stage is reached.
  • Between copepodid stages several moults are shed.
  • Copepodids resemble the adult but are smaller, lack functional sex organs and do not have 5 urosomal segments (these can be difficult to see or may become fused).
  • Copepods are placed into ten orders but only 3 are common in plankton samples: Cyclopoida, Poecilostomatoida and Calanoida. A fourth order, Harpacticoida, contains mainly benthic species that may be captured if the net is fished close to the seabed or brushes against seaweed. Although, there are some truly planktonic harpacticoids. By far the most common copepods in zooplankton samples are calanoids.
  • Members of these orders can be differentiated as follows (after Gibbons 1999):
    • Harpacticoida  Prosome-urosome articulation between the 4th and 5th post-cephalic segments. 1st antenna very short, antenna of 2 parts (biramous ). Urosome usually the same width as prosome.
    • Cyclopoida  Prosome-urosome articulation between the 4th and 5th post-cephalic segments. 1st antenna relatively long, antenna of one part (uniramous). Urosome usually narrower than prosome. Most species occur in freshwater, but there are also common marine species (examples are Oithona spp.).
    • Poecilostomatoida  Prosome-urosome articulation between the 4th and 5th post-cephalic segments. 1st antenna short, antenna uniramous. Usually associated with gelatinous zooplankters (examples are Sapphirina spp.).
    • Calanoida  The prosome-urosome articulation between the 5th and 6th (genital) post-cephalic segments. 1st antenna long, antenna biramous . Urosome usually narrower than prosome (examples are Calanus spp. and Acartia spp.).

Families common to Australia