External Features of Earthworm - QS Study
QS Study

Earthworm

Phylum:   Annelida

Class:        Chaetopoda

Order:       Oligochaeta

Type:         Lampito mauritii

Earthworms are nocturnal animals. They lie in the burrows during the day and come out at night for food. Earthworms leave the burrow only during the rainy season when their burrows are flooded with water.

External features: Lampito (Megascolex) mauritii is a common earthworm found in South India. The body is long, slender, cylindical and bliaterally symmetrical. It is about 8 to 21 cm long and 3 to 4 mm in thickness. The dorsal surface is dark purplish brown, and the ventral surface is paler in colour. It is marked by a series of segments. The segments are separated from one another by inter-segmental grooves. The division is both external and internal. Inside the body, each cavity of the segment is separated from the next, by a thin partition called the septum. All the segments look alike. This kind of repetitive ar-rangement of the segments is called metamerism.

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The mouth is found in the centre of the first segment of the body, called the peristomium. Overhanging the mouth is a small flap called the upperlip or prostomium. The last segment has the anus. It is called the pygidium. In mature worms, segments 14 to 17 may be found swollen with a glandular thickening of the skin called clitellum.

Body setae: Tiny curved bristles called setae are found embedded in small pits of the body wall. These pits are called the setigerous pits. The setae are arranged around the body. They are made of chitin and have a swollen middle part and pointed curved ends. The setae resemble the mathematical symbol ∫. They can be moved in any direction and extended or withdrawn by the action of muscles. They are used for locomotion.