Define Morphology and Anatomy of Earthworm



Earthworms are inhabitants of soil, usually known as ‘farmer’s friend’, due to their role in composting organic wastes into humus. Earthworms have a long cylindrical body, segmented into 100-120 short segments. The dorsal surface of their body is identified by a dark median red dorsal line of the blood vessel, whereas the ventral surface is identified by the presence of genital openings.

The anterior end of the body consists of a promostium, which is a long lobe useful to dig soil, to sensor danger and also covering the mouth below it. The mouth (buccal cavity) is present within the peristomium, which is the first segment of the body. Tutorspoint provide expertise in Morphology and Anatomy of Earthworm Homework Help


A.    Dorsal View               B. Ventral View                     C. lateral view

Segments 14-16 are covered by a prominent glandular tissue known as clitellum. This segment is further divided into three short segments namely, Preclitellar, clitellar and post-clitellar segments.

The 5-9 segments consist of four pairs of spermathecal apertures situated on the ventrolateral sides. A pair of genital pores is present in the 18th segment in male worms. In female worms, the genital pore is present in the mid-ventral line of the 14th segment of the body. Except for the mouth, genital pores, and the clitellar, each body segment consists of rows of S-shaped setae which serve the purpose of locomotion.  The setae can be extended or retracted.



The body wall of the earthworm is externally covered by a thin, non-cellular cuticle, below which single-layered columnar epithelium comprising secretory gland cells, two muscle layers (circular and longitudinal) and an innermost coelom tissue is present.


The Alimentary Canal of Earthworm: A straight tube running from the first to last segment of the body. The alimentary canal starts from the mouth, which opens up to the muscular pharynx, esophagus (5-9 segments) and muscular gizzard (8-9 segments) opening up to stomach in the 9-14 segments. The muscular gizzard acts like a saw to grind the incoming food like vegetable peels and other organic matter. This is then passed on to the stomach, where calciferous glands neutralize the humic acid present in humus.

The intestine starts from the 15th segment covering the entire body and opening into the last segment which is the genital pore. On the 26th segment, the intestine extends into a pair of a short conical structure called intestinal caecae. Further, an internal median fold of dorsal fold called typhlosole is present in the 26-35 segments which serve the purpose of increased absorption in the intestine, thus exhibiting a unique feature of the intestine.

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