Question

1. which trait is characteristic of vertebrates?

they have well - defined skeletons.
they have exoskeletons.
they have no defined organ systems.
they have bilateral symmetry.

Explanation:

Vertebrates are animals with backbones. A well - defined skeleton is a key characteristic. Exoskeletons are found in invertebrates like insects. Vertebrates have defined organ systems. While many vertebrates have bilateral symmetry, it is not exclusive to vertebrates (some invertebrates also have it).

Answer:

They have well - defined skeletons.