an animal has a segmented body, soft fleshy skin, an open circulatory system, it breaths with tiny tubes and openings, and does not have legs or antennae. How would this organism need to change to become an arthropod?

Answer 1

arthropod needs:

open circulatory system
segmented bodies
breathes with tiny tubes and openings
limbs
some types have antennae

Therefore, the arthropod is missing legs