Download Segmented Worms

• True coelom that is
lined
•
Segmented bodies
• Septa: internal walls
between each segment
• Setae: bristles that are
attached to each
segment; used in
respiration
• Filter feeders to predators
• Get their food using a pharynx
• Crop: in earthworms; part of the digestive
system in which food can be stored
• Gizzard: in earthworms; part of the
digestive system in which food is ground
into smaller pieces
• Have complex
organ systems
• Segmented
body
• Closed circulatory system: blood is
contained within a network of blood
vessels
• Blood circulates through two major
blood vessels that run from head to
tail
• Aquatic annelids:
gills
• Land-dwelling
annelids:
diffusion through
their moist skin
• Two kinds of waste
• Digestive waste passes out through the
anus at the end of the digestive tract
• Nephridia: excretory organs that filter fluid
in the coelom
• Well-developed nervous system
consisting of a brain and several nerve
cords
• The sense organs are best developed
in free-living marine annelids
• Hydrostatic skeleton
• Longitudinal muscles and circular
muscles
• Moves by alternating contracting these
two sets of muscles
• Sexually
• Some use external fertilization or have separate
sexes
• Others, such as earthworms and leeches, are
hermaphrodites
– Exchange sperm
– Clitellum: a band of thickened, specialized segments that
secretes a mucus ring into which eggs and sperm are
released and fertilization occurs
– The ring slips off the body and form a protective cocoon for
the worms that hatch a week later
• Oligochaetes
– Streamlined bodies and have relatively few setae
compared to polychaetes, live in soil or fresh
water
• Leeches
– External parasites that suck the blood and body
fluids of their host
• Polychaetes
– Marine annelids that have paired, paddlelike
appendages tipped with setae
• Provide passageways for plant roots and
water and allow the growth of beneficial,
oxygen requiring soil bacteria
• Important in the diet of many birds, moles,
skunks, toads and snakes
• In the sea they participate in a wide range of
food chains
Segmented Worms
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True coelomates; cephalized
Digestive tract with mouth
& anus (tube-within-a-tube)
Closed circulatory system
(blood contained in vessels)
Segmented body
Mouth
Most are marine, but
many live in freshwater
Gut
Examples:
 Earthworms
 Leeches
 Deep ocean
Anus
tube worms
Ectoderm
Mesoderm
Endoderm
Annelids
3 germ layers
Coelom