Transcript Segmented Worms: Phylum Annelida EX: Earthworms

Segmented Worms: Phylum Annelida
EX: Earthworms
A. General Characteristics:
1. Annelid- “little rings”
2. Earthworms, blood-sucking leeches
3. true coelom: body cavity
4. body is divided into segments
5. organ systems are well developed
6. have setae: external bristles that help move and burrow into the dirt.
B. Digestive system/excretory systems
1. mouth and anus
2. feed on soil and organic matter
3. how food moves through digestive system.
a. soil is sucked in by the pharynx and through the mouth.
b. it moves through the esophagus
c. into the crop- storage area
d. Then to the gizzard- grinds up food
e. solid waste are excreted through the anus
f. liquid waste are excreted through nephridia
C. Respiratory system
a. earthworms do not have gills or lungs
b. gas exchange must occur- exchange of oxygen and carbon dioxide.
c. skin must stay moist:
1. secrete mucous
2. thin cuticle that holds moisture
d. If they do not stay moist, they will die
D. Circulatory System
a. closed circulatory system: runs through vessels
b. blood travels from anterior to posterior end by ventral blood vessel
c. blood travels from posterior to anterior end by a dorsal blood vessel.
d. Aortic Arches( 5 hearts)
1. in the anterior end
2. link the dorsal and ventral blood vessels.
3. called 5 hearts because they contract rhythmically to help pump
blood through the system.
4. smaller vessels branch into each segment of the body
E. Movement
a. two types of muscles
1. Longitudinal: Runs anterior to posterior. When they contract, the worm
becomes shorter.
2. Circular: circles around the body of the worm. When they contract, the worm
lengthens (becomes skinnier)
F. Reproduction
a. Hermaphrodites
b. Sexually:
1. two earthworms join head to tail at the clitellum
2. they exchange sperm
3. sperm is stored until eggs are ready to fertilize
4. a mucous sheath is formed around the clitellum
5. eggs and sperm are released into the sheath (cocoon)
6. worm wiggles to slip the sheath off
7. egg and sperm join during the wiggling
8. fertilization occurs
Earthworm Cocoons
Outside structure of an earthworm: Dorsal
side (darker side)
Anterior end
Posterior end
About one third of the way down the earthworm (from the head) is the
clitellum. The clitellum is a swelling of the skin and can only be seen in
earthworms that are ready to reproduce. It may be white, orange-red or
reddish-brown in colour. Earthworms are ready to mate when their
clitellum is orange. Most of the material secreted to form earthworm
cocoons is produced within the clitellum
Underside of Earthworm (Ventral)
(Lighter side)
Prostomium: Tongue like structure used to Sense things.
It is used by the earthworm to “see” its environment - as
earthworms have no eyes, ears, nose or hands, it depends
on the prostomium and skin to help it feel its way through
the soil.
Respiratory, digestive, and circulatory systems of an
earthworm
Dorsal Blood Vessel
Ventral blood vessel
Respiratory System (red):
Pharynx
Nervous system: Brain
(ganglia), ventral nerve cord
5 hearts, dorsal blood vessel,
ventral blood vessel
Digestive System of Earthworm: pharynx, mouth,
esophagus, crop, gizzard, intestine.