Transcript 37-2

Annelida
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Annelid means little
rings, which refer to
body segments
Earthworms and
leeches
15,000 bilateral species
of segmented worms
 have true coelom
 have external bristles
called setae
 some have fleshy
protrusions called
parapodia
3 classes based on number of
setae
1. oligochaeta
earthworms
 no parapodia
 few bristles
3 classes based on number of
setae
2. polychaeta
 bristle worms
 many parapodia
 many bristles
3 classes based on number of
setae
3. hirudinea
 leeches
 no parapodia
 no bristles
 have suckers
Class oligochaeta
 live in soil or fresh water
 most common is earthworm
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
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.
Feeding and digesting
1. Intestines
2. Gizzard
3. Crop
4. Seminal vesicles
5. Seminal receptacles
6. Aortic arches
7. Esophagus
8. Pharynx
9. ganglia
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
Circulation
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
Respiration and excretion
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
Neural control
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.
Reproduction
Earthworm review
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Read pp. 733-736
p.736 1-6
p.737 read bottom 37-2
p.738 2, 4-6, 12-15, 21-24