Annelida

                            Phylum Annelida

Characteristic of Annelida:

Habitat:  Mostly aquatic, some are terrestrial forms.

Body:  Triploblastic, and bilaterally symmetrical. Elongated, cylindrical or flattened body. Body generally divided into segments known as somites or metamere.

Coelom:   Body cavity with true coelom.

Segmentation: True metameric segmentation is present.

Blood:  Red in colour containing haemoglobin which present in plasma.

Heart:  Neurogenic heart occurs.

Circulatory system:  Well developed circulatory and Digestive system is found.

Circulatory system is closed type.

Respiratory System:  Respiratory organ is totally  absent. They respire through their body surface.

Excretion system:  They excrete their waste product by the Nephridia.

Sex:  Hermaphrodite, ( Both male and female reproductive organs is present in single individual )

Reproduction:  They possess both sexual and asexual reproduction. Sexual reproduction accomplished by the formation of gamets.

Fertilization:   External or internal.

Regeneration:   They have regeneration ability.

Development:  Direct ( without formation of any larva ) or indirect ( with formation of larval stage)

Classification of phylum Annelida:

Annelida divided into four major classes.

A. Polychaeta.

B. Oligochaeta.

C. Hirudinea.

D. Archiannelida.

A. Polychaeta:

1. Mostly merine.

2. Body is segmented, locomotory appendages parapodia is present. It bears many long setae help in fixation.

3. They are hermaphrodite and dioceous.

4. Clittelum absent.

5. Occurs closed type circulatory system.

6. Fertilization is internal type.

7. Their development is indirect ( occurs Trochophore larva )

Examples: Nereis ( Sand worm)

                   Aphrodite ( Sea Mouse )

B. Oligochaeta:

1. Thy are either aquatic or terrestrial.

2. Their body lacks a head. The locomotory organ is setae which are small and many in number .

3. Parapodia absent.

4. Clittelum present throughout the life.

5. Cocoon formation occurs.

6. Sexes are united means that they are hermaphrodite but they always perform cross fertilization.

7. Fertilization is external.

8. Occurs direct development.There is no larva in their life cycle.

Examples: Pheretima ( Earthworm ) 

                   Tubifex        ( Blood worm)

C. Hirudinea

1.Found in damp and moist places.

2.Some are Ectoparasites.

3.Parasites are sanguivorous. Hirudin

 ( Anticoagulant) present in their saliva.

4.They are monocious and hermaphrodite.

5.Body segmented, and thirty three (33) number of segments is present in their body.

6.Circulatory system is open type.

7.Clittelum developed during breeding season at the 19th to 21st segment.

8.Five pairs of eyes are present on dorsal side.

9. They lay egg in cocoon.

10. Possess anterior and posterior sucker for locomotion and sucking blood.

11.Development is direct. 

D. Archiannelida:

1. Exclusively marine.

2. Head with tentacles also containing sense organ.

3. Setae and para podia totally absent.

4. Sexes separate or United.

5. Development is indirect with formation of Trochophore larva.

Examples: Polygordilus ( living fossil )

                    Protodrillus.

Excretion in Earthworm through Nephridia:

Excretion: 

Excretion is a process in which the metabolic waste products are removed from the body.

Nitrogenous waste products and CO2 are formed during metabolism and are removed from the body through nephridia.

What is the major excretory organ of  Earthworm?

Ans: Nephridia. The nephridia is ectoderm in origin.

What are the main Waste products  in excretory system of Earthworm?

Ans: Ammonia.

         Urea.

          Water.

          Carbon dioxide.

Types of Nephridia:

There are three kinds of nephridia according to their position in the body.

1. Septal nephridia.

2. Integumentary nephridia.

3. Pharyngeal nephridia.

1. Septal nephridia: ( Present in Septum)

Septum: Septum is the internal wall which 

Separates two segments in Earthworm body.

The nephridia is located intersegmental region of the body.

It occur 15th segment to last segment of the body. That means in first fourteen segments they are absent.

They are well developed and the largest nephridia,and found attached to the both sides of each intersegmental Septum behind 15th segment of the body.

Each Septum has 40-50 nephridia arranged in anterior and posterior in same number , So each segment contains 80-100 septal nephridia except 15th segment which has only 40-50 nephridia.

Nephridia consists of three major parts

Nephrostome or Nephridiostome

Body

Terminal duct

1.Nephrostome: 

It is funnel like structure and externally ciliated and finally opens into the coelomic cavity. It bearing a mouth like opening, which is surrounded by larger upper and lower smaller lip. 

Upper lip contains a large central cell and eight or nine marginal cell, on the other hand the belief formed of 4 or 5 compact cells. The lips have several rows of cilia.

Nitrogenous substance of the coelomicfluid are absorbed in the nephridia due to continuous movement of cilia.

2. Body:

Body consists of two major parts.

Short straight lobe:

 It is short, straight tube like structure remains attached to the twisted loop.

Long twisted loop:

It is long and twisted loop consists of proximal and distal limb to the straight lobe.

3. Terminal Duct:

This structure is end part of the nephridium.

Proximal limbs of nephridium ends into a short a narrow duct known as terminal duct.

Terminal ducts of a segment opens into septal excretory duct of their side. Septal excretory duct collect the waste products and transfer them to a pair of Supra intestinal excretory duct.

Function of Septal Nephridia:

Septal nephridia discharge the waste products by dogs organised into lumen of the intestine. So there enteronephric.

Integumentary nephridia: ( present in skin)

They are attached to the inner side of the body wall from 7th to last segment of the body.

Every Nephridium is  v shaped with short straight and twisted love without presence of nephrostome or funnel. Each segment process 200 to 250 Nephridia but in clitteler region they are number is around 2000 to 2500 so clittelum is also known as  forest of nephridia.

Terminal nephridial ducts are also very short which opens on the outer surface of the body wall by nephridiopores.

Function: Nitrogenous waste materials is directly then out from the body through so they are called exonephric.

Pharyngeal nephridia:

They are found as paired and stay one pair in each of the 4th,  5th,  6th segments of the body. They are similar to septal nephridia in structure but they lack of nephrostome.

In each bunch the terminal duct of the nephridia join together to form a slender duct.

The slender duct   again unite in each segment and formed a thick walled duct which opens into the alimentary canal.

Guanin (Nitrogenous waste materials) extracted from the blood stream by chloragogen cells. The nephridia contains blood gland. It can also help in digestion by secretion of vareity enzymes such as Amylase, Lipase, Dipeptidase, prolidase, chimosin etc. So the nephridia also reffered to as Peptic nephridia.

Function:

West materials directly e-dist Aaj into buccal cavity and fittings from where these are are passed out side with undigested through the anus. They are called enteronephric.