Earthwarm external feature

1. Earthworm
Pheretima Postuma
External Feature
Dr . Sonia Bajaj
H.o.D
Department of Zoology

3. Introduction
• Earthworms are common and very well known to most of us. The common earth-
worm of our country is known as Metairie sp. It is also commonly found in Sri
Lanka, Japan, Australia and South East Asia. It is represented by 13 species in the
Indian .
Habit and Habitat
• Pheretima is a terrestrial earthworm, living in burrows made in moist soil. It
prefers to live in burrow during daytime and at night and rainy season they come
out of their shelter. It is thus nocturnal in habit.
• The castings of earthworm are small rounded pellets or balls that lie at the opening
of the burrow. These castings are formed when it goes deep into the hard and
closely packed soil. The soil upon which it feeds, passes through the body and are
deposited as castings. While burrowing, the earthworm makes the soil loose and
porous.
• The body wastes of earthworm increases the fertility of the soil. So, earthworms
are often said to be the natural tillers of land

4. Structure
• The body of earthworm is elongated, narrow and cylindrical , measuring about 20
cm in length and 3 to 5 mm in width. The anterior end is more pointed than the
posterior end. The dorsal side of the body is brown in colour and can be
distinguished from the ventral side which is lighter in colour.
• The brown colour is due to the pigment porphyrin which is present in the body
wall and it protects the body from bright and strong light. The impression of the
dorsal blood vessel can be seen on the dorsal side as a dark median line extending
throughout the length of the body.
• The body is made up of a series of 100-120 similar segments. This external
segmentation corresponds to internal segmentation and is referred to as metameric
segmentation.
• The segments 14 to 16 from the anterior end are encased in a thick glandular tissue
sheet called the clitellum . Considering the clitellum body may be divided into
two regions, namely the pre-clitellar, clitellar and post- clitellar regions.

6. A distinct ‘head’ is absent in Pheretima. The first body segment is called peristomium
(Greek : peri, around; stoma, mouth) which bears the mouth aperture on the ventral
surface. The peristomium is prolonged anteriorly into a small, fleshy lobe, the
prostomium (Greek: pro, anterior). The last segment, at its posterior end bears the anus.

7. Thanks