Phylum Annelida
True Coelomates with true body segmentation.
Different segments can have different organs
or perform different functions.
There are around 12,000 species of annelids.
Annelids are characterized by 3 principal
features:
1- Repeated Segments
Excretory and locomotory organs
are repeated every segment.
The fluid in each segment creates
a hydrostatic skeleton.
2- Specialized Segments
The anterior segments are
specialized and contain sensory
organs.
A well developed cerebral ganglion is
located in an anterior segment.
3- Connections
Materials and information does pass
between segments.
There is a closed circulatory system.
A ventral nerve cord connects the
ganglia in each segment with the
cerebral ganglion.
The basic body plan is a digestive tract located
within the coelom.
Digestive Tract has several portions:
Pharynx  esophagus  crop 
gizzard  intestine
Annelids use circular muscles and their
hydrostatic skeleton for movement.
Most annelids have segments that possess
SETAE, bristle-like hairs used for
locomotion
Each segment has a pair of nephridia
used to excrete wastes.
Class Oligochaeta
Includes earthworms and some aquatic
worms.
Earthworms have fewer setae than
polychaetes, and no head region or
parapodia.
They do not possess eyes, but do have
many sensory mechanisms.
Class Oligochaeta - the common
Earthworm
Earthworm Locomotion/Muscular System
Digestive System of an Earthworm
Circulatory, Nervous, and Reproductive
Systems
Origin of the Kidney – the
Nephridia
Clitellum – what’s it for?
A glandular swelling that
secretes the cocoon that will
contain the fertilized eggs,
that will of course, grow into
new worms
Class Polychaeta
Marine annelids called bristleworms.
Polychaetes have segments that
possess many setae.
They possess a well developed head
with specialized sense organs.
Each segment has a pair of fleshy
appendages called PARAPODIA.
All annelids have a structure called the
CLITELLUM that secretes a cocoon that is
specialized to receive eggs.
Earthworms are hermaphroditic, meaning
they have both gonads. Why might this
be?
Ewwwwwwwwwwwwwwwwwwwwwwwww!
Ah, but they are sooooooo in love, don’t you think?
Class Hirudinea
Leeches – parasites  .
Are hermaphroditic and produce a
clitellum.
Have suckers at one or both ends for
attachment. Produce a chemical in saliva
called HIRUDIN, which is an anticoagulant
Most leeches have no setae.
Leech Anatomy 101
Mmmm – lunch! 
Leeches Used in Medicine
Successful
reattachment of
severed ear, as
blood continued
to flow and carry
nutrients to the
damaged region
Ready to Suffer?
AssiGnment
1. Your Lab drawings of the Clam are
due.
2. SR/KT on 27.1 on Mollusks was due
Friday.
3. Hwk = 27.2 Annelids – SR/KT
4. Annelid Dissection is Tomorrow,
bring you lab book!