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Anatomy of Animals


Roundworms (phylum Nematoda - meaning thread in Greek), as their name implies, are round rather than flat. They have a smooth outside body wall (called cuticle), indicating that they are nonsegmented. These worms, which are generally colorless and less than 5 cm long, occur almost anywhere and in great variety (15000 known species). There are many thousands of individual nematodes in even a single handful of garden soil. For the simple body plan and genetic sequence as well as the fast life cycle, the C. Elegans become indispensable in the biological research laboratory. Many nematodes are able to suspend their life processes completely when conditions become unfavorable; in these resistant states they can survive extreme dryness, heat, or cold, and then return to life when favorable conditions return. This is known as cryptobiosis - a feature shares
Roundworm Anatomy with the rotifers. Roundworms possess two anatomical features not seen in more primitive animals: a tube-within-a-tube body plan and a body cavity. The body cavity is a pseudocoelom, or a cavity incompletely lined with mesoderm. This fluid-filled pseudocoelom provides space for the development of organs, and serves as a type of skeleton. When roundworms are analyzed according to Table 01, they are seen to have features associated with advanced animals except that they are nonsegmented.

Figure 08b Roundworm Anatomy
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