Have you ever watched how an earthworm, a legless animal, moves ahead?
An earthworm has two pairs of stiff bristles (setae), sticking out from each of its many segments and anchoring the worm as it alternately stretches its body forward and then pulls up the rear. Each segment contains its own set of muscles that make it fatter and shorter.
A leech closely related to an earthworm, has a sucker at each end of its body. With the rear sucker attached, the worm moves its body forward and attaches it at front. When the rear sucker is released, the whole body is pulled forward, the middle temporarily forming a high loop. Inchworms or measuring worms are moth caterpillars that move in a similar fashion but use their front legs plus a set of false legs at the rear.
Starfish creep by suction too. Hundreds of little tube feet lining the groove in each arm work hydraulically, sticking to a surface when water is pumped out and letting go as water fills them once again.
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