Before we get started
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Anterior: head-end
Posterior: tail-end
Dorsal: top-side
Ventral: bottom-side
Phylum Annelida
 many marine, freshwater, and terrestrial
worms
 Ex) leeches and earthworms
 “segmented worms”
– division of rings or segments
 septa/septum (walls) separate segments
 setae: small, bristle-like appendages
Earthworm
Giant Gippsland Earthworm of
Australia
External Anatomy
Internal Anatomy
Musculature
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*Cuticle- thin external layer.
*Epidermis- outer cellular layer
Circular muscle layer
Longitudinal muscle layer
Digestive System
 obtain food by eating through and taking
nutrients from soil
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Mouth
Pharynx
Esophagus
Crop: storage compartment.
Gizzard: soil ground up and churned
Intestine: digestion and absorption occur
Anus: Undigested material is voided
Earthworm Digestion Animation
 http://www.ncsu.edu/scivis/lessons/earthwor
m/Overview.html
Respiratory System
 All annelids live in moist environments
– most are aquatic.
 earthworm can survive only in damp soil.
– Gas exchange occurs at body surface through
diffusion
– No lungs!
Circulatory System
 closed system
 five pairs of pseudohearts surround
esophagus and pump blood
 blood travels to dorsal vessel
Nervous System
 Cerebral ganglia acts as “brain”
 Prostomium: tongue-like lobe above
mouth, allows earthworms to “feel” through
soil
Reproductive System
 Earthworms are hermaphrodites
– male and female reproductive organs present in each
individual
– cross fertilize
 mate by attaching at clitella, exchanging sperm,
then seperating
– sperm stored while clitellum secrete a mucous cocoon
– cocoon slides along worm to collecting sperm and also
eggs
– slips off worm's head
– embryos develop in cocoon.
What happens when an earthworm
is cut in half?
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Can it form two separate worms?
most organs are in anterior
can regenerate a new posterior
posterior end can not regenerate a new
posterior
 so, no you don't get two new worms.
Photographs, Images and text
adapted from
 http://images.google.ca/imgres?imgurl=http:/
/kentsimmons.uwinnipeg.ca/16cm05/16labm
an05/lb6pg2_files/earthworm2.bmp&imgrefu
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