Transcript Section 29.2 Notes

Annelids
Section 29.2
Segmented worms
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Coelomates
2/3rds are marine
Each segment contains digestive, excretory,
circulatory and locomotor organs and is separated
from other segments by septa
Some segments also contain areas responsible for
specific functions such as reproduction, feeding or
sensation
A primitive brain – the cerebral ganglion – is located
at the anterior end, with a nerve cord that runs the
length of the body
Key Characteristics
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Coelom – located inside the mesoderm
Organ systems – including a closed
circulatory system and a one-way gut with
specialized organs
Bristles – stiff, external setae which provide
traction for crawling; some also have fleshy
legs called parapodia
Marine Worms
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The largest group of annelids
Have parapodia for movement
Many are burrowing; some secrete a glue-like
material that sticks grains of sand together to
make a tube
Some are free-swimming predators
Marine Tube Worms glue grains of
sand together to make their tubes
Marine Feather Duster Tube Worms
Marine bristle worm with parapodia
Earthworms
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No parapodia
Only a few seta on each segment
No eyes, but they do have light and touch
sensitive areas on each end of their bodies
Highly specialized scavengers
Body shape is maintained by a hydrostatic
skeleton
They are hermaphrodites
Earthworms are hermaphrodites but
don’t fertilize their own eggs
Leeches
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Have suckers at each end
Most are predators or scavengers
Some are parasites of vertebrates or
crustaceans
No seta or parapodia
No internal segments
Leeches can be useful medicinally