1. AEB 121: INVERTEBRATE ZOOLOGY
PHYLUM ANNELIDA BY
MRS OZEMOKA H. J
ANNELIDA, MOLLUSCA, ARTHROPODA AND ECHINODERMATA
AEB 121: INVERTEBRATE ZOOLOGY. ANNELIDA, MOLLUSCA, ARTHROPODA AND ECHINODERMATA by MRS OZEMOKA H.J. is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

2. PRE TEST / REVIEW What are Annelids?
State three characteristics Of Annelids.
State the three classes of Annelids.
State three differences between the classes of Annelids.
Give three examples of Annelids
State three economic importance of annelids

3. INTENDED LEARNING OUTCOME.
At the end of the week, the students should be able to know:
What Annelids are
the characteristics of Annelids
the various classes of Annelids
the differences between the classes.
the economic importance of Annelids.

4. WHAT ARE ANNELIDS? Segmented worms.
The word was first used by Lamarck for higher segmented worms.
Members of Phylum Annelida.
Derived from Greek word “annelus” meaning little rings.
Includes Earthworm, ragworm, leeches.

5. EXAMPLES OF ANNELIDS
EARTHWORM(OLIGOCHAETE)
LEECHES
NEREIS

6. CHARACTERISTICS OF ANNELIDS.
Bilaterally symmentrical, metamerically segmented with distinct head.
Triploblastic body.
Epithelium secrets outer transparent moist cuticle. Possess segmented bodies which are divided into linear series of cylindrical segments or metameres. Each metamere consist of a section of the body wall and a compartment of the body cavity with its internal organ.

7. ILLUSTRATION OF THE SEGMENTATION
HEAD OR PROSTOMIUM
TRUNK
PYGIDIUM
NOTE: The body is divided into three as illustrated above.
From the image, the yellow segment is PERISTOMIUM.
The green segment is GROWTH ZONE.

8. CHARACTERISTICS CONTINUES.
BODY WALL: The body wall is covered by the epidermis which is secreted by the epidermal cells. The body wall contains well developed segmentally arranged muscles for crawling and swimming movements. Most of the Annelids have short external bristles called setae or chatae which are made of chitin. The setae is for anchorage and also to increase areas of appendages for swimming.

9. CHARACTERISTICS CONTINUES.
DIGESTION: It is complete and extracellular. The digestive glands are found on the body wall. The digestive gut is a straight muscular tube.
OESOPHAGUS
CROP
MOUTH
PHARYNX
INTESTINE
GIZZARD
ANUS
NOTE: The gut is separated from the body cavity by the coelom which is fluid filled. This gives it rigidity. Thus they have HYDROSTATIC SKELETON

10. CHARACTERISTICS CONTINUES.
CIRCULATION: They exihibit a closed circulatory system. It is first developed in the Annelids. Blood flows towards the head through a contractile vessle above the gut and returns to the terminal end. The oxygen carrying pigments vary in this phylum.
Red Oxgen carrying pigment = Haemoglobin
Green oxygen carrying pigment = Chlorocruorin
Pink /Violet oxygen carrying pigment = Haemoerythrin

11. CHARACTERISTICS CONTINUES.
EXCRETION: It involves the use of Nephridia or Metanephridia.
RESPIRATION: It takes place the body wall. In some Poly chaetes, the parapodia which are richly vascularized act as gills.
NERVOUS SYSTEM: lt consist of a brain which is connected by a ring of nerves to a ventral nerve cord that runs the entire length of the body. The various sense organs include: eyes, photoreceptors, chemical receptors, taste buds, tactile tentacles and statocysts (organs of equilibrum).

12. ILLUSTRATION OF CIRCULATORY AND EXCRETORY SYSTEM.

13. CHARACTERISTICS CONTINUES
REPRODUCTION: It is either sexual or asexual. Asexual involves fragmentation, budding or fission. The oligochaetes and Polychaetes have a high ability to regenerate lost parts. As regards sexual reproduction, sexes may be separate (bisexual) or united (unisexual or hermaphrodite). For bisexual, development is indirect with a trochophore Larva while unisexual have direct development.
Fertilization is external but internal in Hirudineans. Cleavage is holoblastic and spiral.
ECOLOGY
They are cosmopolitan

14. TROCHOPHORE LARVA Apical tuft(Cilia) Prototroch(Cilia) Mouth
Metatroch(Cilia).
Mesoderm
Anus

15. CLASSIFICATION OF ANNELIDS
POLYCHAETA
HIRUDINEA
OLIGOCHAETA
Class Polychaeta - mostly marine worms, such as Nereis (the clamworm) ,
Class Oligochaeta - mostly freshwater and terrestrial worms, such as Lumbricus (the Earthworm).
Class Hirudinea - the leeches (predominantly freshwater), such as Hirudo.

16. POLYCHAETE Exclusively marine. Possess many setae or chaete
Absence of clitellum
Sexual reproduction.
Fertilization is external (if it is internal, brooding occurs in the body of the worm).
Some possess tentacles which can be used for respiratory and feeding.

17. TYPES OF POLYCHAETES
There are two types based on mode of existence namely:
Errantia: active swimmers or crawlers.
Sendentaria: bottom dwellers and are sedentary found attached to mud, crevices, rocks etc.

18. OLIGOCHAETES Few setae Hermaphrodites Detritous Presence of clittelum
Mainly terrestrial and fresh water
Example is earthworm

19. HIRUDINIA Mainly leeches Inhabit fresh water habitat
Presence of suckers both anterior and posterior.
Dorsoventrally flattened.
Exihibit variety of colours such as black, brown, red or olive green.
They are carnivorous on small invertebrates. Some are parasitic on fishes.
They have clitellium which appears only during breeding season.
They have a fixed number of segments.

20. ECONOMIC IMPORTANCE.
Earthworm enriches the soil as well as ensures aeration of the soil
Leech is of medical importance for bleeding patient, healing severed appendages.
Leeches produces antibiotics, anticoagulant and anaesthetics.

21. ASSIGNMENT
In a tabular form, state the differences between the three classes of annelids.