morphology of animals

1. EARTHWORM
dr.aarif

2. EARTHWORM
- Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the
moist soil.
- During day time, they live in burrows made by boring and swallowing the soil.
- In the gardens, they can be traced by their faecal deposits known as worm castings.
- The common Indian earthworms are Pheretima and Lumbricus.

3. EARTHWORM : Morphology
- Earthworms have long cylindrical body.
- The body is divided into more than hundred short segments
which are similar (metameres about 100-120 in number).
- The dorsal surface of the body is marked by a dark median mid
dorsal line (dorsal blood vessel) along the longitudinal axis of
the body.
- The ventral surface is distinguished by the presence of genital
openings (pores).
- Anterior end consists of the mouth and the prostomium, a lobe
which serves as a covering for the mouth and as a wedge to
force open cracks in the soil into which the earthworm may
crawl.
- The prostomium is sensory in function.

4. EARTHWORM : Morphology
CLITELLUM :
- The first body segment is called the peristomium (buccal segment)
which contains the mouth.
- In a mature worm, segments 14-16 are covered by a prominent dark
band of glandular tissue called clitellum. It secretes mucus and albumen
for the formation of cocoon or egg capsule.
- Thus the body is divisible into three prominent regions – preclitellar,
clitellar and postclitellar segments
SETAE :
- In each body segment, except the first, last and clitellum, there are rows
of S-shaped setae, embedded in the epidermal pits in the middle of
each segment.
- Setae can be extended or retracted.
- Their principal role is in locomotion

5. EARTHWORM : Morphology
APERTURES :
- Four pairs of spermathecal apertures are situated on the ventro-lateral
sides of the intersegmental grooves, i.e., 5th -9th segments.
- A single female genital pore is present in the mid-ventral line of 14th
segment.
- A pair of male genital pores are present on the ventro-lateral sides of
the 18th segment.
- Numerous minute pores called nephridiopores open on the surface of
the body

6. EARTHWORM : Digestive System
ALIMENTARY
CANAL
FEATURES & FUNCTIONS
1. MOUTH Terminal opening in peristomium overhung by prostomium
2. BUCCAL
CAVITY
extends from 1st to 3rd segment
3. PHARYNX Small pear shaped sac from middle of 3rd segment to end of 4th segment
4. OESOPHAGUS narrow tubular structure from 5th to the 7th segment
5. GIZZARD Prominent, oval, hard and thick walled muscular organ in segment 8th and 9th.
It grinds the food with the help of thick muscles and cuticle
6. STOMACH Short narrow and tubular structure from 9th to the 14th segment. Highly vascular and
glandular walls.
The chalky secretion of the calciferous glands neutralise the humic acid in the humus
7. INTESTINE Intestine starts from the 15th segment onwards and continues till the last segment.
A pair of short and conical intestinal caecae project from the intestine on the 26th
segment.
The characteristic feature of the intestine between 26-35 segments is the presence of
internal median fold of dorsal wall called typhlosole. This increases the effective area
of absorption in the intestine.
8. ANUS The alimentary canal opens to the exterior by a small rounded aperture called anus

7. EARTHWORM : Circulatory System
- Pheretima exhibits a closed type of blood vascular system, consisting of blood vessels, capillaries and heart.
Due to closed circulatory system blood is confined to the heart and blood vessels.
- Heart : 4 pairs of tubular hearts, 7th and 9th segment : lateral hearts whereas 12th and 13th segment :
lateral oesophageal hearts
- Anterior Loops : Thin walled ,non pulsatile loop like broad vessels without valves in 10th and 11th segment
- Blood Vessels : Weel organised vessels which run along the body of earthworm
i) Dorsal blood vessel : largest blood vessel of the body running mid dorsally above the alimentary canal
from one end of the body to the other. It has valves and receives blood from
various parts of the body
ii) Ventral blood vessel : Also extends from end to end but it does not have valves. It is the main
distributing vessel.

8. EARTHWORM : Circulatory System
- Blood Glands : In segments 4th, 5th, and 6th lying above the pharyngeal mass are small red coloured follicular
bodies called as blood glands. They produce blood corpuscles and haemoglobin.
- Blood : made up of colourless plasma and blood cells. The respiratory pigment,haemoglobin is present in the
plasma and helps in transport of oxygen. The only type of blood cell is the leucocyte and hence is phagocytic
in nature.

9. EARTHWORM : Excretory System
NEPHRIDIA FEATURES & FUNCTIONS
1. Pharyngeal three paired tufts in the 4th, 5th and 6th segments
2. Integumentary attached to lining of the body wall of segment 3 to the last that
open on the body surface
3. Septal present on both the sides of intersegmental septa of segment
15 to the last that open into intestine
- These different types of nephridia are basically similar in structure
- Nephridia regulate the volume and composition of the body fluids.
- A nephridium starts out as a funnel that collects excess fluid from coelomic
chamber.
- The funnel connects with a tubular part of the nephridium which delivers the
wastes through a pore to the surface in the body wall into the digestive tube.

10. EARTHWORM : Nervous System
All the activities of the earthworm are under the control of the nervous system.
The Nervous System is made up of an Anterior Nerve ring and Posterior Nerve
cord
Nervous system is basically represented by ganglia arranged segment wise on the
ventral paired nerve cord.
Nervous System Features and Functions
Nerve ring &
Nerve cord
- The nerve cord in the anterior region (3rd and 4th
segments) bifurcates, laterally encircling the pharynx and
joins the cerebral ganglia dorsally to form a nerve ring.
- The cerebral ganglia along with other nerves in the ring
integrate sensory input as well as command muscular
responses of the body

11. EARTHWORM : Reproductive System

12. EARTHWORM : Male Reproductive System
FEATURES & FUNCTIONS
Testis sacs There are two pairs of testis sacs in the 10th and 11th segments. Each sac
encloses a testis and a spermiducal funnel
Testis - There are two pairs of testes in 10th and 11th segments.
- Each testis arises from the anterior wall of each testis sac.
- Immature spermatozoa produced by the testes first enter testis sacs and
then make their way into seminal vesicle where they undergo further
development to become mature sperms.
Seminal
Vesicle
There are two pairs of seminal vesicles in 10th and 11th segments
Spermiducal
funnel
- There are two pairs of spermiducal funnels one in 10th segment and the
other in 11th segment.
- Each spermiducal funnel leads into a fine tube, the vas deferens.
Vasa deferentia - There are present two pairs of vasa deferentia. Each spermiducal funnel leads
into a vasa deferens.
- Vasa deferentia of each side run very close to each other upto the 18th
segment. In 18th segment, both the vasa deferentia of each side are joined to
the prostate duct coming from the prostate gland.
- Two vasa deferentia ducts and one prostate duct of each side are enclosed in
a common thick muscular sheath called the common prostate and spermatic
duct. They open to the outside separately into male genital aperture.

13. EARTHWORM : Male Reproductive System
FEATURES & FUNCTIONS
Prostate - A pair of large prostate glands are present in earthworm.
- These glands are situated on either side of the intestine and extend from the
16th to the 21st segment.
- They produce a secretion, which serves as a medium for transfer of sperms
Accessory
glands
- There are two pairs of whitish glandular masses situated internally in 17th
and 19th segments.
- The secretion of these glands is supposed to help in keeping the two worms
close together during copulation

14. EARTHWORM : Female Reproductive System
FEATURES & FUNCTIONS
Ovaries There is a pair of white minute masses of the ovaries attached to the
posterior surface of the septum present between the 12th and 13th
segments. They produce ova.
Oviducts - They are two short tubes each lying immediately behind the
respective ovary.
- The two ovarian tubes converge to meet in the body wall and open
to outside by a female genital aperture on mid-ventral side of the
14th segment.
- The mature ova liberated by each ovary are received by the oviducts
and are finally passed outside into the cocoon through a female
genital aperture
Spermathecae - There are present four pairs of spermathecae which lie in the 6th,
7th 8th and 9th segments.
- They open to outside through the spermathecal pores situated
ventro-laterally in the successive grooves separating the above
mentioned segments. They store the sperms received from another
earthworm during copulation

15. EARTHWORM : Fertilization
- A mutual exchange of sperm occurs between two
worms during mating.
- One worm has to find another worm and they mate
juxtaposing opposite gonadal openings exchanging
packets of sperms called spermatophores.
- Mature sperm and egg cells and nutritive fluid are
deposited in cocoons produced by the gland cells of
clitellum.
- Fertilisation and development occur within the
cocoons which are deposited in soil.
- The ova (eggs) are fertilised by the sperm cells within
the cocoon which then slips off the worm and is
deposited in or on the soil.
- The cocoon holds the worm embryos. After about 3
weeks, each cocoon produces two to twenty baby
worms with an
average of four.
Earthworms development is direct, i.e., there is no larva
formed.