Download The Annelida - Blue Valley School District

The Annelida
Major Characteristics
• Animal Characteristics
• Cylindrical, Bilateral, &
Segmented
• Triploblastic
• Eucoelomate
• Complete Digestive
System
• Closed Circulatory
System
Classification
• Class Polychaeta
(many hairs)
• Class Oligochaeta
(few hairs)
• Class Hirudinae
(Leeches)
Body Plan
• Annelids contain a true
cavity or coelome that is
located between layers
of mesoderm
• They are the first major
phyla that showing
segmentation
(metamerism) which is
advantageous to
movement, safety, and
tagmatization
Movement
• Each annelid segment
contains its own longitudinal
and circular
• These muscle work
antagonistically, such that
when the longitudinal
muscles contract the circular
muscles relax and the
segment become short and
thick
• In contrast, when the circular
muscles contract, the
longitudinal muscles relax
and the segment becomes
long and thin
Feeding
• Annelids have a complete
digestive system and are
protostomes (mouth forming
first)
• Their system contains
mouth, pharynx, esophagus,
crop, gizzard, intestine and
anus
• They use muscle to help in
the mechanical digestion of
food
Reproduction
• Oligochaetes are
monoecious and during
copulation they line up
facing in the opposite
direction from each
other
• The clitellum secretes a
mucous that holds the
worms in place
• Later the clitellum acts
as a cocoon where the
fertilized egg develops