What characteristic do sea stars and brittle stars have in common? Both have flexible joints.
Both have teeth-like feeding structures.
Both use tube feet to catch prey.
Both have tentacles.

They typically have a tough, spiny surface, which inspired their name (in Greek, echinos means “spiny” and derma means “skin”). They also have the unusual ability to regrow lost body parts, and sea stars and brittle stars can regrow arms if broken off or eaten

Explanation:

both have a touch spiny surface and they both have the ability to regenerate limbs

there really is life in the deepest part