Transcript 27-3 Annelids

27-3 AnnelidsSegmented Worms
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27-3 Annelids
What Is an Annelid?
I. What Is an Annelid?
A. Annelids are worms with segmented
bodies. They have a true coelom that
is lined with tissue derived from
mesoderm.
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27-3 Annelids
What Is an Annelid?
II. Three Germ Layers of an Annelid
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27-3 Annelids
What Is an Annelid?
A. The body of an annelid is divided into segments.
B. Each segment is separated by septum, which
are internal walls between each segment.
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27-3 Annelids
What Is an Annelid?
A. Body segments may carry eyes, antennae, other
sense organs, or be specialized for functions such
as respiration.
B. Bristles called setae may be attached to each
segment.
C. Annelids have a tube-within-a-tube digestive tract
that food passes through from the mouth to the
anus.
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27-3 Annelids
Form and Function in Annelids
III. Form and Function in Annelids
A. Annelids have complex organ systems.
B. Many of these systems are unique because of
the segmented body plan of this group.
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27-3 Annelids
Form and Function in Annelids
A. In earthworms, the pharynx pumps food and soil
into the esophagus.
B. The food then moves through the crop, where it
can be stored.
C. It then moves through the gizzard, where it is
ground into smaller pieces.
D. The food is absorbed farther along in the digestive
tract in the intestine.
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Form and Function in Annelids
IV. Circulation
A. Annelids typically have a closed circulatory
system, in which blood is contained within a
network of blood vessels.
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27-3 Annelids
Form and Function in Annelids
B. Blood in the dorsal (top) vessel moves toward the
head of the worm.
C. The dorsal blood vessel functions like a heart
because it contracts rhythmically and helps pump
blood.
Dorsal blood
vessel
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27-3 Annelids
Form and Function in Annelids
A. Blood in the ventral (bottom) vessel runs from
head to tail.
Ventral blood
vessel
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27-3 Annelids
Form and Function in Annelids
D. In each body segment, a pair of smaller blood
vessels connect the dorsal and ventral blood
vessels and supply blood to the internal organs.
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27-3 Annelids
Form and Function in Annelids
V. Respiration
A. Land-dwelling annelids take in oxygen and give
off carbon dioxide through their moist skin.
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27-3 Annelids
Form and Function in Annelids
VI. Excretion
A. Digestive waste passes out through the anus.
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27-3 Annelids
Form and Function in Annelids
VII. Response
A. Most annelids have a well-developed nervous
system consisting of a brain and several nerve
cords.
Brain
Ganglia
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Form and Function in Annelids
VIII. reproduction
A.When eggs are ready for fertilization, a clitellum
secretes a mucus ring into which eggs and sperm are
released.
B.A clitellum is a band of thickened, specialized
segments.
C.After eggs are fertilized in the ring, the ring slips off
the worm's body and forms a protective cocoon.
D.Young worms hatch weeks later.
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Groups of Annelids
IX. Oligochaetes
A.Oligochaetes contains earthworms and their
relatives.
B.Oligochaetes typically have streamlined
bodies and relatively few setae compared
to polychaetes. Most oligochaetes live in
soil or fresh water.
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Ecology of Annelids
X. Ecology of Annelids
A. Earthworms and many other annelids spend
their lives burrowing through soil, aerating and
mixing it.
B. Earthworms help plant matter decompose.
C. Earthworm castings are rich in nitrogen,
phosphorus, potassium, micronutrients, and
beneficial bacteria.
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