Final answer:
Arthropods are ecdysozoan protostome bilateral animals due to their membership in the Ecdysozoa group, the presence of protostome embryonic development, and their bilateral symmetry.
Step-by-step explanation:
Arthropods are ecdysozoan protostome bilateral animals because they exhibit several key features. Firstly, they belong to the Ecdysozoa superphylum, which includes organisms that undergo exoskeletal molting or ecdysis. Secondly, arthropods are protostomes, which means that during early embryonic development, the blastopore becomes the mouth. Lastly, they have bilateral symmetry, meaning their body can be divided into right and left sides that are mirror images of each other.