THE  ANNELIDA

• Characteristics
  1. protostomes
  2. metamerism (segmentation) [Fig. 22.3]
  3. hydrostatic skeleton
  4. longitudinal and annular muscles [Fig. 22.6]
  5. paired setae [Fig. 22.14]
  6. nephridia [Fig. 22.9]
  7. well developed nervous system [Fig. 22.8]
  8. closed circulatory system [Fig. 22.7]

Polychaeta- Star Horseshoe fanworm, St. Kitts.; photograph courtesy of BIODIDAC 

Class POLYCHAETA

• 5,300 species
• mainly marine, infaunal and epifaunal
• mobile [Fig. 22.5] and sessile [Fig. 22.1]
• carnivores, detritus feeders, and filter feeders
• mostly dioecious
• parapodia [Fig. 22.6]

Class OLIGOCHAETA

• earthworms [fig. 22.11] and others
• 3000 species
• few setae: use muscles for locomotion [Fig. 22.12]
• mainly freshwater and terrestrial
• most are deposit feeders, fertilize and aerate the soil [Box 22.1]
• hermaphroditic, but cross fertilize [Fig. 22.15]
• clitellum

Class HIRUDINEA [Fig. 22.16]

• leeches; 500 species
• mostly freshwater
• predators: invertebrates and blood
• no setae
• anterior and posterior muscular suckers
• medicinal uses [Box 22.2]
• more medicinal uses
• see Mark Siddall and E. M. Burreson's Hirudinea Pages for more information

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