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 like humans develops into the spinal cord). While some chordates may have well - developed senses or brains (like vertebrates), not all chordates (e.g., some primitive chordates like lancelets) have highly developed senses or brains. But the defining trait for the phylum Chordata is the presence of a structure that is related to the spinal cord (the notochord at some stage of development, which is replaced by the spinal cord in many chordates).

Answer:

possess a spinal cord.