Annelida

• Sometimes called "segmented worms"

  
• Annelida


  • Bilateral Symmetry
  • Metameric body
  • They respire through their body surface
  • They have a well-developed circulatory and digestive system
  • Their body contains hemoglobin, which gives them a red color
• Coelomate


  Having a body cavity
• Triploblastic

  Having three germ layers
• Setae

  • Bristle-like structures attached to the body wall
  • Provide traction for movement and help anchor the worm in the substrate
  • They vary in number, size, and arrangement depending on the species and habitat

  
• Parapodia


  • Paired, paddle-like appendages along the body segments
  • Equipped with setae and can be used for swimming, burrowing, crawling, or even gas exchange
  • Especially well-developed in polychaete annelids, which are primarily marine worms

  
• Nephridia are responsible for removing metabolic wastes and maintaining osmotic balance
• Closed Circulatory System

  • Blood is confined to vessels and does not directly bathe the tissues
  • Consists of blood vessels and a pumping organ called the heart, which propels blood through the body
• Nervous System

  • Ladder-like nervous system consisting of a pair of ventral nerve cords that run along the length of the body, one on each side
  • The nerve cords are interconnected by transverse nerves and ganglia, or nerve clusters, located in each body segment
  • The ganglia serve as local processing centers for sensory and motor information

  
• Prostomium


  • A distinct head region which lies in front of the mouth
  • May bear sensory organs such as eyes, antennae, and palps

  
• Peristomium


  • The first body segment behind the prostomium and typically surrounds the mouth

  
• Clitellum


  • Smooth midpiece that is present at sexual maturity
  • Secretes mucous during reproduction
• Sexual Reproduction (Internal Fertilization)

  Earthworms locate potential mates through chemical cues released in their mucus trails or by physically encountering another worm

  
• Asexual Reproduction (regeneration)


  • Many annelids have remarkable powers of regeneration
  • They can replace lost parts, and some species have break points that allow worms to sever themselves when a predator grabs them
  • Lost segments are later regenerated
  • Some polychaetes reproduce asexually by budding or by transverse fission

  
• Scientific name: Nereis virens, Common name: Clamworm
• Scientific name: Lumbricus Terrestris, Common name: Earthworm

  
• Scientific name: Hirudo medicinalis, Common name: Medicinal leech