Notochord, Dorsal nerve chord and Gill-slits are features seen in :
(a) vertebrata
(b) protozoa
(c) mollusca
(d) porifera
(a) The defining characteristic of a vertebrate is considered the backbone or spinal cord, a brain case, and an internal skeleton, but the latter do not hold true for lampreys, and the former is arguably present in some other chordates.
