Annelida: Segmented Bodies
Segmented Bodies
The fundamental characteristic of the phylum is the division of the body into a linear series of cylindrical segments, or metameres. Each metamere consists of a section of the body wall and a compartment of the body cavity with its internal organs. The external divisions, which may be seen in the common earthworm, correspond to the internal divisions. The annelid body consists of a head region; a trunk, made up of metameres; and an unsegmented terminal region called the pygidium. In some primitive members of the phylum the metameres are identical, or very similar to one another, each containing the same structures; in more advanced forms there is a tendency toward a consolidation of some segments and a restriction of certain organs to particular segments. Because of the soft nature of the annelid body, fossils are not common. Fossils of tube-dwelling polychaetes have been found, but there is scarcely any fossil record for earthworms and none for leeches.
Sections in this article:
- Introduction
- Leech Reproduction
- Leech Predation and Digestion
- Leech Anatomy
- Class Hirudinea
- Oligochaete Reproduction
- Oligochaete Circulation and Respiration
- Oligochaete Digestion
- Oligochaete Anatomy
- Class Oligochaeta
- Archiannelida and Myzostomaria
- Polychaete Reproduction
- Polychaete Anatomy
- Sedentary Polychaetes
- Errant Polychaetes
- Class Polychaeta
- Reproduction
- The Nervous System
- Respiration
- Circulation
- Digestion
- The Body Wall
- Segmented Bodies
- Bibliography
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