Annelida

• Phylum Annelida

  The True Segmented Worms

  
• Characteristics of Annelids

  • Found in marine, freshwater, and terrestrial habitats
  • Vermiform, bilaterally symmetrical, and segmented body
  • Each segment separated by a transverse septum
  • Triploblastic body with a well-developed coelom
  • Covered with a flexible non-chitinous cuticle
  • Most forms have setae
  • Complete digestive system
  • Closed circulatory system
  • Excretory system typically consists of a pair of metanephridia per segment
  • Exhibit Metamerism

  
• Metamerism


  The serial repetition of internal and external morphological features in each body segment
• Overall body structure

  • Divided into head (Prostomium), body, and tail (or pygidium)
• Classes of Annelida

  • Class Polychaeta
  • Class Oligochaeta
  • Class Hirudinea
• Class Polychaeta

  • Ragworms
  • Fanworms
  • Clam worms

  
• Class Polychaeta characteristics

  • Mostly marine and free-living
  • Multiple setae on fleshy lateral outgrowths known as parapodia
  • Well-developed head bearing appendages
  • Sexes separate with a free-swimming Trochophore larva

  
• Notable Polychaetes

  • Nereis (Ragworm)
  • Feather Duster worms
  • Clam worms
  • Christmas Tree worms

  
• Class Oligochaeta

  • Earthworms
  • Freshwater worms

  
• Class Oligochaeta characteristics


  • Mostly terrestrial with a few freshwater species
  • Relatively few setae
  • Complete absence of parapodia
  • No distinct head appendages
  • Clitellum present in mature individuals
  • Hermaphrodites with copulation required
  • Eggs deposited in a cocoon with direct development

  
• Class Hirudinea


  • Leeches
• Class Hirudinea characteristics


  • Majority are parasites (ectoparasites)
  • Usually dorso-ventrally flattened with 34 body segments
  • No setae or parapodia
  • Clitellum present only during reproduction
  • Two suckers – anterior and posterior
• Annelids' Ecological & Economic Importance

  • Burrowers and surface dwellers
  • Loosen soil for water and oxygen penetration
  • Super detritivores involved in decomposition
  • Used as bait for fishing
  • Food source for various animals
  • Involved in traditional medicine practices
• Some annelids are involved in traditional medicine to cure ailments such as bladder stones, jaundice, piles, diarrhea, etc.
• Leeches are often used in traditional medicine for bloodletting to remove "bad" blood associated with various disease conditions, known as Hirudotherapy.