Which is incorrect about non-chordates ?

Central nervous system is ventral, hollow and double.

The correct answer is Option (4) -Central nervous system is ventral, hollow and double.

Animals belonging to phylum Chordata are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits . These are bilaterally symmetrical, triploblastic, coelomate with organ-system level of organisation. They possess a post anal tail and a closed circulatory system.