Phylum Annelida – segmented worms
• body composed of repeating
segments (metamerism)
• many possess setae, chitinous
bristles along the length of body
• fluid filled cavity with much
flexibility (hydrostatic skeleton)
• Two part head with a prostomium,
and peristomium and posteriorly
the pygidium
• possess both logitudinal and
circular muscles; peristaltic
contraction
• closed circulatory system
• Three class groups – polychaetes
(many hairs); oligochaetes (few
hairs); Hirudinea (leeches)
Figure 7.15c
Class Polychaeta
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“many” “chaete = hair”
Most of marine annelids
Have a well differentiated head
Segments have paddle-like appendages called
parapodia(um)
Some crawl freely in search for food (bristleworm)
Some live in burrows and often feed on sediments or
suspension feeders (lugworm)
Some build tubes and suspension feed (tube worms)
Palolo worms breed using bioluminescence to spawn at
surface
Figure 7.15a
Figure 7.15b
Social Feather
Duster Worm
Lug worm
Class Oligochaeta – “few hairs”
• Appear smooth; lack
parapodia
• Mainly in sand or mud and
feed on detritus
• Earthworms are
monoecious and cross
fertilize
• Produce a mucus cocoon
form clitellum where young
embyronate and hatch as
juveniles
Class Hirudinea
• Leeches are parasitic (blood suckers); most are
freshwater, but some are marine
• Most have a fixed number of body segments (34)
• Have anterior and posterior suckers and a
• Produce hirudin, an anticoagulant to aid in blood feeding,
such as in Hirudo medicinalis
Leech on Shrimp
Leech