2. Phylum Annelida
• (L. annelus, little ring, ida, pl. suffix) consists of the segmented
• 15,000 species
• worms whose bodies are divided into similar segments,
(metameres) arranged in linear series and externally marked by
circular rings called annuli
• Sometimes called “bristle worms” because most annelids bear tiny
chitinous bristles called setae
Functions of Setae
- terrestrial annelids – locomotion
- aquatic forms - swimming
3. Body Plan:
• The annelid body typically has a two-part head, composed of
a prostomium and a peristomium followed by a segmented
body and a terminal portion called the pygidium bearing an
• Peritoneum (a layer of mesodermal epithelium) lines the body wall of
each compartment, forming dorsal and ventral mesenteries that
cover all organs
• Hydrostatic skeleton
– coelom is filled with fluid.
5. Class Polychaeta
• Polychaeta (Gr. polys, many, chaite¯, long hair) with more than
• Many polychaetes are euryhaline.
• Polychaetes differ from other annelids in having a well differentiated
head with specialized sense organs; paired appendages, called
- paired appendages of polychaete that function in locomotion and
Polychaetes are often divided into two morphological groups
based on their activity:
- Sedentary polychaete
- Errant polychaete
8. Form and Function:
• the prostomium, which may or may not be retractile and which often
bears eyes, tentacles, and sensory palps
- The peristomium surrounds the mouth and may bear setae,
- digestive system consists of a foregut, a midgut, and a hindgut.
- Foregut - includes a stomodeum, a pharynx, and an anterior
- Midgut - secrete digestive enzymes but absorption takes place
toward the posterior end.
- Hindgut - connects the midgut to the exterior via the anus, which is on
10. Circulation and Respiration:
• parapodia and gills serve for gaseous exchange in various species.
• circulatory pattern varies greatly
• In Nereis blood flows between these two vessels via segmental
networks in the parapodia, septa, and around the intestine.
• In Glycera the circulatory system is reduced and joins directly with
the coelom. Septa are incomplete, and thus the coelomic fluid
assumes the function of circulation.
- either protonephridia or metanephridia.
• Dioecious – separate sexes
13. Class Oligochaeta
• 3000 species of oligochaeta
• include the familiar earthworms and many species that live in
• Most are terrestrial or freshwater forms, but some are parasitic
Ex. Chaetogaster limnaei
Forms and Body Function:
- Earthworms use peristaltic movement: Contractions of circular
muscles in the anterior end lengthen the body, pushing the anterior end
forward where it anchors.
- Differ from polychaetes, no parapodia
15. Circulation and Respiration :
- Have a double transport system: coelomic fluid and a closed
• coelomic fluid – carries food, wastes, and respiratory gases.
• closed circulatory system – which includes capillary systems in the
• Most are scavengers.
• - feed mainly on decaying organic matter, bits of leaves and
vegetation, and animal matter.
• bears a pair of metanephridia.
• - occupies parts of two successive segments :ciliated
funnel & Nephrostome
18. Class Hirudinida
• Leeches are between 2 and 6 cm in length, but some, including
“medicinal” leeches, reach 20 cm.
• The giant of all is the Amazonian Haementeria (Gr. haimateros,
bloody) (which reaches 30 cm!!!!!)
• flattened dorsoventrally
Form and Function:
• Leeches are more highly specialized than oligochaetes.
- they don’t have setae but have sucker for attachment and for
• Leeches crawl with looping movements of the body, by attaching first
one sucker and then the other and pulling the body along the surface.
• Leeches are popularly considered parasitic, but many are
1. Fresh water leech
- active predators or scavengers equipped with a proboscis
that can be extended to ingest small invertebrates or to take blood from
Ex. medicinal leech, Hirudo medicinalis
2. Terrestrial leech –
- feed on insect larvae, earthworms, and slugs,which they
hold by an oral sucker while using a strong sucking pharynx to ingest
Ex. Haemadipsa sp.
3. Marine Leech
- Common hosts Fish, sharks and rays that live on exterior
surface, fins, anus, gill cavity, and spiracle.
Ex. Stibarobdella loricata
• The coelom of leeches has been reduced by the invasion of
connective tissue and, in some, by a proliferation of chloragogen
tissue, to a system of coelomic sinuses and channels.
• Leeches are hermaphroditic but cross-fertilize during copulation.
1. 1.Sperm are transferred by a penis or by hypodermic impregnation
(a spermatophore is expelled from one worm and penetrates the
integument of the other).
2. 2.After copulation their clitellum secretes a cocoon that receives
eggs and sperm.
3. 3. Leeches may bury their cocoons in mud, attach them to
submerged objects, or, in terrestrial species, place them in damp
similar to that of OLIGOCHAETES..
22. Largest leech
- Haementeria ghilianii- It can grow to 450 mm (17.7 in) in length and 100
mm (3.9 in) in width
1-3. Enumerate the 3 classes of Phylum Annelida and give 1
4. Difference between protonephridia and metanephridia.
5. Function of prostomium in polychaete.
6. Function of peristomium in polychaete.
7. What do you call the movement in which there is contractions
of circular muscles in the anterior end lengthen the body, pushing
the anterior end forward where it anchors.
8. What do you call the paired appendages of polychaete that
function in locomotion and breathing.
9-10. What are the two transport system in class oligochaeta and
give their functions.