Annelida

• Annelida


  Segmented worms

  
• Classes of Annelids


  • Polychaeta
  • Oligochaeta
  • Hirudinea
• Body cavity


  Space between outer body wall and digestive tract (Coelom)

  
• Peritoneum


  Covers the coelom and all organs within it
• Characteristics of Annelida


  • Segmentation
  • Chaetae (Hairs made of Chitin)
  • 3 Cell Layers
  • Head develops first (Protostomal)
• Polychaeta


  • Live in the ocean (marine)
  • Many chaetae (chitinous hairs)
  • Movement: Paired parapodia for swimming/crawling, may burrow using peristalsis
  • Feeding: Deposit feeders, raptorial predators, herbivores/scavengers, filter feeders
  • Reproduction: Dioecious, segmentation allows regeneration and epitoky

  
• Oligochaeta


  • Live in freshwater, land, ocean
  • Few chaetae (chitonous hairs)
  • Movement: Burrow with peristalsis, use chaetae as anchors
  • Feeding: Deposit feeders, herbivores/scavengers
  • Reproduction: Hermaphroditic

  
• Hirudinea


  • Mostly freshwater, some marine
  • No chaetae
  • Movement: Mostly using suckers on both ends
  • Feeding: 3/4 blood-sucking ectoparasites, 1/4 predators
  • Reproduction: Hermaphroditic
• The phylum Annelida is made up of segmented worms, numbering about 15,000 species

  
• Protostome


  Annelids have a coelom made from cell masses
• Metamerism


  Coelom is divided into a series of repeated parts, each segment is called a metamere
• Except for the head and tail region, each segment in an annelid is ring like and very similar
• Coelomate


  Annelids normally have long thin bodies composed of a series of identical segments
• Growth in Annelids


  1. Lateral enlargement of segments during juvenile stages

  2. Addition of new segments produced by the foremost section of the pygidium
• Characteristics of Annelida


  • Bilaterally symmetrical and vermiform
  • Body has more than two cell layers, tissues and organs
  • Body cavity is a true coelom, often divided by internal septa
  • Body possesses a through gut with mouth and anus
  • Body possesses 3 separate sections, a prosomium, a trunk and a pygidium
  • Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve chord
  • Has a true closed circulatory system
  • Has no true respiratory organs
  • Reproduction normally sexual and gonochoristic or hermaphoditic
  • Feed a wide range of material

  
• Metamere


  A section of the body wall and a compartment of the body cavity with its internal organs
• Pygidium


  Unsegmented terminal region of the annelid body
• Body wall


  • Covered with epidermis overlaid with a thin, pliant cuticle
  • Well-developed, segmentally arranged muscles
  • Most possess short external bristles called setae or chaetae, composed of chitin
• Digestive system


  • Unsegmented gut that runs through the middle of the body from mouth to anus

  
• Circulatory system


  • Usually closed, with blood containing hemoglobin or other pigments
  • Blood flows toward head through contractile vessel above gut, returns to terminal region through vessels below gut

  
• Respiration


  • Some have thin-walled, feathery gills
  • Most have no special organs, respiration occurs directly through body wall
• Nervous system


  • Primitive brain in head region, connected by nerve ring to ventral nerve cord
  • Sense organs include eyes, taste buds, tactile tentacles, statocysts
• Reproduction


  • Sexual or asexual
  • Asexual by fragmentation, budding, or fission
  • Sexual reproduction common, often hermaphroditic
  • Fertilized eggs develop into free-swimming larvae or hatch as miniatures
  • Ability to regenerate lost body parts highly developed in many

  
• Polychaete reproduction


  • Most reproduce sexually with separate sexes
  • Fertilization usually external in seawater, forming free-swimming larvae
  • Some undergo extreme changes, with portion containing sex cells breaking off to swarm and spawn

  
• Oligochaeta


  • Includes about 3,500 species of earthworms and freshwater worms
  • Most are burrowers in soil, but also inhabit other environments

  
• Hirudinea


  • Includes 500 species of leeches, flattened predacious or parasitic annelids with suckers
  • Primarily freshwater, some marine or terrestrial
  • Majority are predators on small invertebrates, some are blood-sucking parasites
  • Hermaphroditic with internal fertilization, eggs deposited in cocoons

  
• Annelids have two main modes of existence: quiet life in holes or more active lives
• Segmentation allows flexibility and mobility, and evolved twice - in protostomes (Annelida, Arthropoda) and deuterostomes (Chordata)
• Annelida


  Segmented worms

  
• Classes of Annelids


  • Polychaeta
  • Oligochaeta
  • Hirudinea
• Body cavity


  Space between outer body wall and digestive tract (Coelom)
• Peritoneum


  Covers the coelom and all organs within it
• Characteristics of Annelida


  • Segmentation
  • Chaetae (Hairs made of Chitin)
  • 3 Cell Layers
  • Head develops first (Protostomal)
• Polychaeta


  • Live in the ocean (marine)
  • Many chaetae (chitinous hairs)
  • Movement: Paired parapodia for swimming/crawling, may burrow using peristalsis
  • Feeding: Deposit feeders, raptorial predators, herbivores/scavengers, filter feeders
  • Reproduction: Dioecious, segmentation allows regeneration and epitoky
• Oligochaeta


  • Live in freshwater, land, ocean
  • Few chaetae (chitonous hairs)
  • Movement: Burrow with peristalsis, use chaetae as anchors
  • Feeding: Deposit feeders, herbivores/scavengers
  • Reproduction: Hermaphroditic
• Hirudinea


  • Mostly freshwater, some marine
  • No chaetae
  • Movement: Mostly using suckers on both ends
  • Feeding: 3/4 blood-sucking ectoparasites, 1/4 predators
  • Reproduction: Hermaphroditic
• The phylum Annelida is made up of segmented worms, numbering about 15,000 species

  
• Protostome


  Annelids have a coelom made from cell masses
• Metamerism


  Coelom is divided into a series of repeated parts, each segment is called a metamere
• Except for the head and tail region, each segment in an annelid is ring like and very similar