Q.Give the differences between chordates and non-chordates, with a sketch.
[!ANSWER] Chordata is set apart from every non-chordate phylum by a specific combination of four structural hallmarks.
Every chordate possesses, at some point in its life cycle, a notochord (a flexible dorsal supporting rod, often later replaced by a vertebral column), a dorsal, hollow (tubular) nerve cord running above the notochord, a series of paired pharyngeal gill slits connecting the pharynx to the exterior, and a post-anal tail extending behind the anus.
Non-chordate phyla lack this specific combination entirely. Where a nerve cord exists in a non-chordate animal — for example, the ventral nerve cord found in Annelida and Arthropoda — it is solid, not hollow, and is positioned on the ventral (lower) side of the body rather than the dorsal (upper) side. Non-chordates also entirely lack a notochord and, correspondingly, never develop a vertebral column.
A simple comparative sketch would show, on one side, a generalised chordate in longitudinal section with the hollow nerve cord above the notochord, above the gut (with gill slits in the pharyngeal region) and a tail extending behind the anus; and on the other side, a generalised non-chordate (such as an annelid) with a solid nerve cord running along the ventral side of the body, and no notochord, gill slits, or post-anal tail anywhere in its structure.
[!ANSWER] Chordates: notochord + dorsal, hollow nerve cord + pharyngeal gill slits + post-anal tail. Non-chordates: no notochord, and any nerve cord present is solid and ventral (e.g. Annelida) — a fundamentally different body plan.
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