Q.(a) Differentiate chordates and non-chordates. OR

Chordates are unified by four hallmark features — notochord, dorsal hollow nerve cord, pharyngeal gill slits, and post-anal tail — that non-chordates never possess.

Answering part (a): Differentiate chordates and non-chordates.

Chordates (Phylum Chordata — e.g., fishes, amphibians, reptiles, birds, mammals):

1. Possess a notochord — a flexible, rod-like supporting structure running along the back — present at least at some stage of life (embryonic or throughout, depending on the group).
2. Have a dorsal, tubular (hollow) nerve cord lying above the notochord, which develops into the brain and spinal cord.
3. Possess paired pharyngeal gill slits in the pharynx region at some stage of life (used for respiration in aquatic forms, or modified into other structures in terrestrial forms).
4. Have a post-anal tail — a tail that extends beyond the anus — present at least during embryonic development.
5. Typically have an internal (endo-) skeleton and a closed circulatory system with a ventral heart.

Non-chordates (all other animal phyla — e.g., Porifera, Cnidaria, Platyhelminthes, Annelida, Arthropoda, Mollusca, Echinodermata):

1. Lack a notochord at any stage of life. …