The crustacean group of copepods are to the sea and to freshwater lakes and rivers what insects are to the land. They are small, abundant both individually and in species, and occupy almost every conceivable niche. Many are free-swimming planktonic forms complete with “oar-feet” (the English translation of their Greek name), long antennae, and rudderlike tail. Still others have lost some or all of their appendages and are completely parasitic on fish or other marine animals. The earliest and best known copepod, Calanus finmarchicus, was first discovered in Norwegian seas in 1767. In the present century, it has been found that it is the principal food of the English herring, and also of the sei whale in Antarctic waters. A very similar species, Calanus australis, occurs in New Zealand waters where it undoubtedly is an important fish food. Calanus, which is about an eighth of an inch long, is one of the larger copepods. In inshore and harbour waters, most species are relatively small and these include Acartia, Temora, and Paracalanus, which is just like a midget Calanus. Since they are so small it is usually necessary to have a microscope to study their intricate shape and colouring, often very bright and beautiful. One species, Sapphirina, often found in northern waters, can easily be seen by a diver or a swimmer with goggles, because its whole body is a brilliant iridescent blue which glints in the sunlight on a bright day.
by Richard Morrison Cassie, M.SC.(N.Z.), D.SC.(AUCK.), Senior Lecturer in Zoology, University of Auckland.