Anatomy

A common feature uniting all the copepod orders is a single simple eye in the middle of the head, at least in the larval stage. The cephalosome, a shield over the head and some thoracic segments distinguishes the free living forms. Most are very small, less than 1 mm long, but rare oceanic species are over 1 centimetre.

There are several different forms of copepods arranged into ten groups called orders. It is not a simple matter to distinguish the orders of copepods, and impossible without a good microscope. Few biologists attempt to identify copepods beyond the level of order but species diversity has been found by those that have to be very high. Most of the free-living species belong to only three orders. The rest are usually parasitic, some barely recognisable as crustaceans except when larvae.

Biology

Free-living copepods will be found only by towing very fine nets, certainly less than quarter-millimetre mesh, through a pond or sea-water, or by washing the fauna off marine algae through a net of this kind. Animals which may appear only as a tiny speck to the naked eye may be copepods but their identity demands most detailed microscopic examination of preserved specimens.

Being so small, free-living copepods can feed only on small food items like bacteria, diatoms or other unicellular forms. Eggs produced by the female copepod are carried in clusters in one or a pair of egg-sacs attached to the base of the abdomen. Females like this are easy to recognise as copepods.

Feedback and queries should be sent to the Discovery Centre at Museum Victoria.
Please note, the Discovery Centre can help you only with questions about crustaceans from southeastern Australia. It can not advise on the care of pet hermit crabs or on crustaceans from other regions.