A primitive muscular system exists simply as tiny long muscles that run the length of the body that help the worm to thrash around.
(A primitive muscular system; exists simply; ) (as tiny long muscles; run; the length of the body) (the body; help; the worm to thrash around) (the worm; to thrash; around)
A primitive muscular system as tiny long muscles the body the worm
exists simply run help to thrash
the length of the body
the worm to thrash around
around