Describe external features of earthworm
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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.
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.
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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.
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.
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The external features (morphology) of earthworm :
- Earthworms have long, narrow, cylindrical body.
- Their body is divided into short and similar segments.
- These similar segments are known as metameres. They are about 100 to 120 in number.
- These metameres divide body both externally and internally, such type of segmentation is called metameric segmentation or metamerism.
- These segments are separated from each other by distinct ring-like grooves or annuli.
- The dorsal surface of their body is recognised by a dark median/mid-dorsal line, which is in fact a dorsal blood vessel beneath the skin.
- Their ventral surface can be recognised by the presence of genital apertures (pores).
- The earthworms do not possess a distinct head nor any specialised sense organs-like eyes or ears.
- So, the anterior end of these worms consist of mouth and the prostomium.
- Mouth is a crescentric aperture at the anterior end of first segment. This segment is known as peristomium (or buccal segment).
- The dorsal edge of peristomium projects forward above the mouth, as a small fleshy lobe called prostomium which serves as covering for the mouth. It is used as a muscular probe in burrowing. It is also sensory in function.
- Other external features of earthworm include – presence of clitellum, setae and various apertures
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