Transcript Ch. 10 Phylum Annelida

Ch. 10 Phylum Annelida
Segmented worms
Segmentation
• Divisions of body sections.
• Earthworm has about 100 segments
External earthworm
• Anterior end is darker and more pointed than the
posterior.
• Clitellum (enlarged segments that form a band
around segments 32-37) is closer to the anterior.
• The mouth and prostomium (upper lip) is at the
anterior end.
• Anus is the opening at the posterior end where
waste exits.
Setae
• Tiny bristles on the sides of the earthworm
used for movement and to cling to the sides
of its burrow or underground tunnel.
• Each segment has 4 pairs of setae except for
the first and last segments.
• The setae and muscles of the worm work in
coordination to push and pull the worm by
contracting and extending the body.
Earthworm setae
Internal Earthworm
Digestive System
1.
2.
3.
4.
5.
Pharynx- muscular organ for sucking in soil that contains food
particles.
Esophagus- long tube that connects the pharynx with the crop.
Crop-round structure that temporarily stores food.
Gizzard-round, muscular structure used to grind food. Contractions
along with sand particles help physically grind up the food.
Intestine- Stretches from segments 19 to anus. This organ
chemically breaks down food and allows it to be absorbed into the
bloodstream. Undigested food is released as castings.
Earthworm castings help to
fertilize the soil. The tunnels help
create holes to let oxygen and
water to plant roots.
Circulatory System
• Blood carries food and oxygen
to all cells.
• The earthworm has a closed
circulatory system. Blood is
contained inside of tubes.
• Dorsal and ventral blood
vessels are main two tubes that
carry blood to anterior and
posterior regions and back.
• Aortic arches are 5 branching
tubes that pump the blood. Not
a true heart.
Respiratory System
• Earthworms have a thin skin that is able to
absorb oxygen and give off carbon dioxide.
The skin is protected by a thin cuticle. The
skin must be kept moist by mucus in order
for the gases to be diffused.
Excretory system
• Nephridia are tiny tubes located in each
segment of the body. They remove cellular
waste and clean the blood. (Similar to the
function of the human kidney.) Openings on
the ventral side called nephridiopores allow
the waste to exit the body.
Nervous system
• The brain is found in segment 3. It is
attached to a ventral nerve cord. Ganglia,
enlarged nerve centers, are found in each
segment.
• Earthworms have specialized cells in their
skin to respond to light and sound.
Reproductive system
• Earthworms are hermaphroditic. They have both
male and female organs in the same body.
However, earthworms must cross-fertilize and
exchange sperm.
• Sperm is produced in the testes and is stored in the
seminal vesicals. Eggs are produced in a pair of
ovaries. They leave the ovaries and mature in the
body cavity. Earthworms line up side by side and
exchange sperm. Sperm from each worm is stored
in the seminal receptacles until the eggs are
fertilized when laid.
Eggs are released into a slime
ring secreted by the clitellum.
• Fertilization occurs and the slime ring
slips off the body and forms a cocoon,
where the young worms develop.
1.
Giant earthworm found in Africa
and Australia.