Nematode Worms

Draconema - a marine nematode.  Photo: Darwin Project

Nematodes (also known as round worms), named from the Greek word nematos, meaning thread, are found in almost every imaginable kind of ecological niche.  

Although only about 15,000 have been described by scientists so far, it has been estimated that there may be closer to 500,000 species of nematodes.

Nematodes live in the sea, in fresh water, and in soil from the polar regions to the tropics, from under rocks in Antarctic Adelie penguin colonies, to the Great Barrier Reef. Nematodes have been discovered on the very highest mountain tops, and in the greatest depths of the oceans. Scientists estimate that good top soil will contain billions of nematodes per hectare. But nematodes are also pests. They parasitise almost every species of animal and many plants, indeed nematode infestations can be so devastating that they are one of the most important of all the world's parasitic animal groups.

The characteristics of nematodes include:

• A body that is bilaterally symmetrical or cylindrical in shape;
• A body covered with a secreted, flexible, non-living cuticle, similar to the material from which our fingernails are made;
• Moveable cilia and flagella are completely lacking; and
• Muscles in the body wall run in a longitudinal direction only. 

There are a few other things that make nematodes special. Most are under 5 cm long, and many are microscopic. Some of the parasitic nematodes may be over 1 m in length.