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Annelida 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 vessel1. dorsal blood vessel carries blood to anterior end2. 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 Read pp. 733-736 p.736 1-6 p.737 read bottom 37-2 p.738 2, 4-6, 12-15, 21-24