Annelida: Class Polychaeta

The vast majority of the more than 8,000 known species of polychaete worms are marine; some, however, are found in fresh or brackish water. They are abundant from the intertidal zone to depths of over 16,405 ft (5,000 m). The polychaetes, so named because of the numerous setae (chaetae) they bear, range in length from less than 1⁄8 in. to more than 9 ft (2 mm to 3 m), but most are from 2 to 4 in. (5–10 cm) long. Their colors are often brilliant, and some species are iridescent. The class has usually been divided on the basis of mode of existence into two groups, the errantia and the sedentaria.

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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