How do starfish, mollusks and earthworms move? I need this asap.

Starfish-

Starfish are equipped with hundreds of tiny little feet at the end of each arm. To move, they fill these feet with seawater, causing the arm to move like a foot would. This mechanism allows the starfish to move - much quicker than you might expect.

Mollusks-

Most mollusks move with a muscular structure called a foot. The feet of different kinds of mollusks are adapted for different uses, like crawling, digging, or catching prey. ... These are mollusks like snails and slugs that have just one shell or no shell at all. Gastropods creep along on their broad foot.

Earthworms-

An earthworm moves using circular and longitudinal muscles, as well as bristles called setae. The earthworm can push the setae out of its body to grab the soil around it. To move forward, the worm uses its setae to anchor the front of its body and contracts the longitudinal muscles to shorten its body.

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The answer is a because - is an direction