Transcript Phylum Annelida: Segmented Worms

Phylum Annelida:
Segmented Worms
• Body composed of segments separated by
internal partitions (appears as little rings
around the body of the worms)
• Greek word “annellus” means little ring
• Includes earthworms, exotic seafloor
worms, and leeches
Segmented Worms
Body Systems
Circulation
• Have a closed
circulatory system
that includes vessels
Respiration:
• Aquatic annelids
breathe using gills
• Terrestrial annelids
diffuse oxygen
through their moist
skin
Segmented Worms Body Systems
Nervous System
• Most annelids have a well developed
nervous system consisting of a brain and
several nerve cords
Digestion
• Digestion occurs as food passes through a
tube-like digestive system with two ends
(mouth and anus)
• Range from filter feeders to fearsome
predators (at least for their size)
Movement of Segmented Worms
Have longitudinal and circular muscles
• Longitudinal muscles run parallel to the
length of the worm and contract to make
the worm shorter and fatter
• Circular muscles wrap around each body
segment and contract to make the worm
longer and thinner
• Movement is obtained by alternating
contractions of these muscles
Segmented Worm Reproduction
Sexual Reproduction
Only!
• Typically includes a
male and female
• Segmented worms
are hermaphroditic
• Fertilization occurs
externally
External Fertilization
• Two Hermaphroditic individuals swap sperm
simultaneously
• The sperm are stored in special sacs on the
body until the eggs are ready for fertilization
• The eggs and sperm are released into a
mucus ring that slips off the end of the
worms’ body and forms a protective cocoon
• Young hatch two to three weeks later
Classes of Annelids
Class Oligochaeta – (Oligochaetes) –
earthworms and their relatives found in
soil and fresh water
Class Hirudinea – leeches; parasites that
suck blood.
– Most feed on snails, worms, and insect larvae
Class Polychaeta – (Polychaetes) –
sandworms and bloodworms
Earthworms: Friend or Foe?
• Spend their lives
burrowing in soil,
aerating it, and mixing
it to depths of two
meters or more.
• But do they decrease
the amount of duff
(organic matter;
leaves) leading to
changes in the
ecosystem