Annelida

1
Annelida

• 15,000 bilateral species
• of segmented worms
•    have true coelom
• have external bristles
• called setae
•    some have fleshy
• protrusions called
• parapodia

• Annelid means little rings, which refer to body
  segments
• Earthworms and leeches

2
3 classes based on number of setae

• 1. oligochaeta
• earthworms
•  no parapodia
• few bristles

3
3 classes based on number of setae

• 2. polychaeta
•   bristle worms
•  many parapodia
• many bristles

4
3 classes based on number of setae

• 3. hirudinea
•  leeches
•   no parapodia
• no bristles
• have suckers

5
Class oligochaeta

•  live in soil or fresh water
• most common is earthworm

6
Structure and movement

•  more than 100 segments
• circular and longitudinal muscles line
  interior body wall
• muscles contract, worm moves forward and
  setae grip the ground. Coelom is fluid filled and
  gives pressure on ground. This is locomotion

7
Feeding and digesting

•  soil is sucked in by muscular pharynx
• passes through esophagus
• enters crop which is a temporary storage area
• passes into gizzard which grinds the soil to
  release organic material
• passes into intestines where nutrients are
  absorbed
• anus is at the end of the digestive tract where
  waste materials pass out
• worms are a burrowing animal and this helps the
  soil. This allows nutrients and oxygen to get in
  for plant roots, aerates the soil and loosens the
  soil.

8
Feeding and digesting

• 1. Intestines
• 2. Gizzard
• 3. Crop
• 4. Seminal vesicles
• 5. Seminal receptacles
• 6. Aortic arches
• 7. Esophagus
• 8. Pharynx
• 9. ganglia

9
Circulation

• closed circulatory system
• has dorsal and ventral blood vessel
• 1. dorsal blood vessel carries blood to anterior
  end
• 2. ventral blood vessel carries blood to
  posterior end
• aortic arches
• 5 pairs of muscular tubes connecting the 2
  vessels together
• located in the anterior end
• contractions cause blood to move

10
Circulation
11
Respiration and excretion

• no special respiratory organs
• oxygen and carbon dioxide diffuse through skin
  (moist skin)
• nephridia are excretory organs. They are
  located in all segments but the first three and
  last one. These release excretions through
  ventral pores

12
Respiration and excretion
13
Neural control

• have ganglia connected to ventral nerve cord
• each segment has ganglia but anterior segment
  has a few ganglia fused into the cerebral
  ganglion. This is where most senses are sensed
  light, touch, chemicals, moisture, temperature,
  and vibrations

14
Neural control
15
Reproduction

• hermaphrodites
• no self-fertilization
• 2 worms come close together with ventral
  surfaces and anterior ends pointing in opposite
  direction
• clitellum (thickened section of body) secretes
  mucus to hold worms together.
• Each worm injects sperm into mucus. The sperm
  travels to seminal receptacle of other worm. A
  hard tube called chitin takes eggs to sperm and
  fertilization occurs in tube.

16
Reproduction
17
Earthworm review

• Read pp. 733-736
• p.736 1-6
• p.737 read bottom 37-2
• p.738 2, 4-6, 12-15, 21-24