Phylum Annelida
Leech
Segmented Worms
Fireworm
Christmas tree worm
Feather duster worm
Annelid Characteristics
• Segmentation =
Metamerism
– metameres
(=somites, segments)
– Show true
segmentation - both
internal and external
– Allows for
specialization
Annelid Systems
All systems found in Annelids but skeletal
• Complete digestive tract - some
specialization - crop and gizzard
• Closed circulatory system - is segmentally
arranged dorsal and ventral vessels aortic
arches (hearts)
Annelid Systems
All systems found in Annelids but skeletal
• Excretion
– Nephridia segmentally
arranged
Annelid Systems
All systems found in Annelids but skeletal
• Nervous system
– ladder shaped
– pair of cerebral
ganglia
– double ventral nerve
cords
– pair of ganglia in
each segment
– several sensory
structures
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•
•
•
taste buds
tactile organs
eyes in some
statocyst
Annelid Systems
• Reproduction
– some are monoecious, others dioecious
– marine species have trochophore larvae
– some have asexual reproduction by
• Budding
• fragmentation
Annelid Systems
• Respiration
– across body surfaces
– some have gills
– some use parapodia
Class Polychaeta
• Make up 2/3 of
phylum
• most primitive
annelids; ancestral to
other two classes
• almost all are marine,
few freshwater species
Polychaet Characteristics
• differentiated
head
– Tentacles
– first segment
• Prostomium
• Peristomium
• Mouth
– Palps
– eyes
Polychaet Characteristics
• Parapodialateral
appendages
– notopodiumdorsal
– neuropodiumventral
– acicula- rods
• Respiration
– By parapodia
Polychaet Characteristics
• Reproduction
– sexes separate
– no permanent gonads
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•
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•
egg and sperm form from coelomic peritoneum
pass out of nephridia or burst thru body wall
fertilization is external in sea
free swimming larva- trochophore
Polychaet Ecological Types
• free living- all are
predators
• tube dwelling- all are
filter feeders
– secrete their own tube
– burrow into substrate
Class - Oligochaeta
• Terrestrial or Freshwater
• No distinct head - but contains pro- and
peri- stomium
• Clitellum - present at all times
– Used in copulation
– Cocoon production
Class - Oligochaeta
• Reproduction
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–
–
–
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Monoecious
Copulation
Internal fertilization
Eggs laid in cocoon
no larval stage
Class - Oligochaeta
• Digestive system - well differentiated
– mouth
– pharynx
– crop
– gizzard
– intestine - Typhlosole
– Anus
Class - Oligochaeta
• Circulatory system
– Closed
– 5 pairs of aortic arches
– Hemoglobin
• Respiration
– Body surface
• Excretion
– Nephridia
Class - Hirudinea
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Freshwater or terrestrial
Have suckers
Segmentation fixed (34 segments)
Clitellum only during season
Digestive tract
– large crop
– Anticoagulant
• Medically important