It has a central and a peripheral nervous system. It has a double transport system composed of coelomic fluid that moves within the fluid-filled coelom and a simple, closed blood circulatory system. It conducts respiration through its skin. An earthworm's digestive system runs through the length of its body. Earthworms are commonly found living in soil, feeding on live and dead organic matter. Is Rockall mud, with its vast numbers of practically identical nematodes, really richer than a rainforest, with its staggering array of insect life? I’ve yet to inspect the Rockall Trough myself but I think I can guess the answer.An earthworm is a tube-shaped, segmented worm found in the phylum Annelida. Insects, on the other hand, are fantastically varied, with a diversity of form that is unparalleled in the animal world. Morphologically, nematodes are a notoriously conservative lot – it might be said that once you have seen one, you have seen them all. But before we telegate insects to the ranks of second best, perhaps we should think a little more about the difference between species numbers and species diversity. If this is the case, the previous holders of the title – the insects – come a poor second, with between a tenth and a third of that number of species, depending on whose estimates one favours.
So now the truth is out: nematodes are the most species diverse forms of animal life, with perhaps as many as 100 million species worldwide (This Week, 16 September).
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