Commonly known as roundworms, nematodes are one of the most diverse of all animal phyla making them rather difficult to distinguish. With an estimated 1 million members, they are also one of the largest.
Nematodes are typically small, most not exceeding an inch or two. However, some parasitic roundworms can be longer. Their bodies are often ornamented with distinctive structures like ridges and rings. They typically have many lips (3 to 6) and a series of teeth.
Their epidermis is either one or many layers of skin tissue covered by collagenous cuticle. This may also have a few layers. Muscle cells are found underneath the epidermis. They extend the length of the organism. Since they have no skeletons, muscles serve as a hydrostatic skeleton. Strangely, nematodes have no circular muscles. Each muscle cell is composed of fibers and a semifluid cytoplasm known as the sarcoplasmic portion of the cell.
Click one of the following links to see more of three types of roundworms.
Click one of the following links to see more of three types of roundworms.