Anatomy and Physiology of Earthworm

by Balogun Wasiu Gbolahan

Anatomy and Physiology of Earthworm General overview External anatomy Nervous system Digestive system Circulatory system Excretory system Respiratory system Reproductive system Muscular system Skeletal system Special senses Why Study Earthworm?

General overview•Phylum: Annelida

•Shape: tube-shaped

•Body structure:

metamerically segmented

•Habitat: inside the

earthworm or moist

places

•Feed: live or dead

organic matter

External Anatomy

Nervous system

Nervous system• The Peripheral nervous system

a. Eight to ten nerves arise from the cerebral ganglia to

supply the prostomium, buccal chamber and pharynx.

b. Three pairs of nerves arise from the sub-pharyangeal

ganglia to supply the 2nd, 3rd and 4th segment.

c. Three pairs of nerves extend from each segmental ganglia

to supply various structures of the segment.

• The sympathetic nervous system consists of nerve plexuses

in the epidermis and alimentary canal.

Digestive system

Circulatory systemThe earthworm has a closed circulatory system. An earthworm circulates blood exclusively through vessels. Presence of haemoglobin

Excretory system• The excretory system contains a pair of

nephridia in every segment, except for the first three and the last ones.

• The three types of nephridia are:1. The integumentary nephridia lie

attached to the inner side of the body wall in all segments except the first two.

2. The septal nephridia are attached to both sides of the septa behind the 15th segment.

3. The pharyngeal nephridia are attached to fourth, fifth and sixth segments.

Respiratory system• There is no formalized respiratory system in

earthworms; exchange of oxygen and carbon dioxide takes place through the moist cuticle.

• Respiration normally occurs in air but earthworms can exist in water for long periods of time (e.g. for six months) if the water is oxygenated.

Reproductive system

Copulation and Fertilisation

Muscular systemUseful•Movement•Digestion of food

Skeletal system• They lack either an internal skeleton or

exoskeleton, but maintain their structure with fluid-filled coelom chambers that function as a hydrostatic skeleton.

Special senses• The Epidermal Receptors: These are found all over the

epidermis but are more numerous on the lateral and ventral surface of the body. Earthworms are very sensitive to touch and to vibrations transmitted through solid objects.

• Buccal Receptors: They are found in large numbers in the epithelium of buccal cavity. These are olfactoreceptors and gustatoreceptors. Thus the earthworms can recognize different types of leaves that can be used as food.

• Photoreceptors: They are found in the inner parts of the epidermis. The photoreceptors are restricted to the dorsal surface and are more numerous on the prostomium and first segment. The photoreceptors enable the worm to detect changes in the intensity of light.

Photoreceptor cells in Prostomium

Why Study Earthworm?• Understanding of animals for our own education

and management purposes.• Choose appropriate animals models to study

disease.• Add to human cultural base.• Studying soil pollution.• Vermicomposting.• Bait for fishing.

Links for further reading• http://www.sas.upenn.edu/~rlenet/Earthworms.

html• http://www.northallegheny.org/Page/19944• http://ibis.geog.ubc.ca/biodiversity/efauna/Earth

wormsIntroduction.html• http://cronodon.com/BioTech/Earthworm_NS.ht

ml• http://passscience.blogspot.my/2010/09/reprodu

ctive-system-of-earthworm.html

Thank you for your

time