Introduction

Abstract

There is a general belief among biologists that nematodes are mainly parasitic, however large numbers of free-living nematodes inhabit marine- or fresh-watermud and the soil and several million can be found per square metre in the top few centimetres of sub-littoral mud. These free-living nematodes feed upon bacteria, fungi, decaying materials and microscopic animals. They are seldom seen, however, as most of them are less than a millimetre in length. Nematodes are widely distributed and are found in almost every type of environment.

They occur in arid deserts and at the bottom of lakes and rivers, in the waters of hot springs and in the polar seas where the temperature is constantly below the freezing point of fresh water. They were thawed out alive from Antarctic ice in the far south by members of the Shackleton Expedition. They occur at enormous depths in Alpine lakes and in the ocean. As parasites of fishes they traverse the seas; as parasites of birds they float across continents and over high mountain ranges.¹

Some will survive for many months in liquid nitrogen; others live in unusual habitats such as vinegar, bill posters’ paste or drip mats that have been soaked in beer. A number of species are cryptobiotic and can survive for months or years in an almost desiccated state until water becomes available, when they revive. Nematodes also feed on living plants, either as ecto- or endoparasites, and they are one of the important groups of invertebrate parasites of animals and man.