THE  ANNELIDA

 

PHYLUM ANNELIDA

segmented worms; 10,000 species [Fig. 22.1]

  • 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

         Images courtesy of BIODIDAC

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