Question

all the animals within the phylum chordata...
possess all these traits.
have some well - developed senses.
have a well - developed brain.
possess a spinal cord.

Explanation:

Chordates are defined by having a notochord (which in vertebrates develops into the spinal cord), dorsal - hollow nerve cord, pharyngeal slits, and a post - anal tail at some stage of their life. While some chordates may have well - developed senses or brains (like vertebrates), not all do (e.g., tunicates as adults have a simple nervous system). But all chordates possess a structure related to the spinal cord (the dorsal - hollow nerve cord which becomes the spinal cord in many).

Answer:

possess a spinal cord.