HSEB zoology notes | Setae of pheretima posthuma (Earthworm)

V.S of body wall in earthworm

(Setae = Locomotion organ in Pheretima or Earthworm)

In earthworm , each segment of body except 1st segment, clitellum region and last segment(anus) bears chitinous row of setae. They are insoluble in KOH . They are arranged in ring like form in middle of each segments and are in 80-180 in number. Each setae of earthworm is elongated , 'S' shaped in structure and faint yellow in colour having sollen structure in the middle called the nodules. The half portion of setae is embedded in body wall and half portion of setae is projected upon body surface which helps earthworm for locomotion. Setae consists of three parts i.e neck , nodules and base.

In earthworm, locomotion is also assisted by musculature of body wall and hydraulic skeleton. When the pressure on the coelomic fluid rises the cuticle becomes very hard which is called as hydraulic skeleton.

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