Answer: The earthworm contracts and extends in its movement, but the nematode moves side by side.
Explanation:
NOTE: By mode of location, we mean the way it moves.
The skin of a nematode is very unusual in that it secretes a thick outer cuticle which is both hard and flexible. And this cuticle makes it sustain a side by side mode of location. The closest thing a roundworm has to a skeleton is its cuticle and it uses it as a support and balance point for movement. Long muscles lie just underneath the epidermis and are all aligned longitudinally along the inside of the body, so the nematode can only bend its body from side to side, not contract or extend itself.
Whereas the earthworm extends and contracts as its mode of location.
An earthworm moves by using its two different sets of muscles: circular muscles for looping around each segment, and the longitudinal muscles for running along the length of the body.
The contraction of the circular muscles make the earthworm stretch becoming longer and thinner. The earthworm uses its longitudinal muscles to contract and thus becomes shorter and wider or it bends from one side to the other, pulling the body forward in the process. The earthworm withdraws the front setae and uses its rear setae to anchor itself at the back. Then the earthworm uses its circular muscles to lengthen and push itself forward again.
