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