Practical Zoology: A Study Guide - T. A. Dauda 2014
Multicellular Animals
Roundworms
Roundworms are widely distributed. They inhabit the bottom of freshwater and marine bodies of Water, as well as damp soil; many species parasitize the bodies of various plants, invertebrates, and vertebrates, as well as humans. Their unsegmented bodies are, in most cases, spindle-shaped and circular in cross-section. Metamerism is absent. There are no Organs of locomotion (except for the Skin-muscular sac). A primary body cavity—the pseudocoel—is present, lacking an epithelial lining. The Internal Organs are situated within the body cavity. The Digestive System is formed by a straight tube that begins with the Mouth and ends with the anus. It consists of anterior, middle, and posterior regions. The anterior and posterior sections of the gut are of ectodermal origin, while the middle section is derived from the endoderm. Respiratory and circulatory systems are absent. The excretory system does not communicate with the body cavity and has a unique Structure. The Nervous system is primitive, and Sense Organs are poorly developed. They are dioecious. The reproductive apparatus is considerably simpler than that of Flatworms and, in typical cases, has a tubular structure.
Among the several classes belonging to the phylum of roundworms (Nemathelminthes), the Class Nematoda, or true roundworms (Nematoda), possesses the greatest practical significance and species diversity.
Last update: 13/08/2026
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