Biology · Animal Kingdom · NEET
The notochord. A notochord is a flexible rod-like structure that forms on the dorsal (back) side during embryonic development. Animals that form it are chordates; animals that never form it are non-chordates (from Porifera up to Echinodermata). NEET often tests only this one line, so it must be your anchor.
NCERT lists four features present at some stage of life: (1) a notochord, (2) a dorsal hollow (single) nerve cord, (3) paired pharyngeal gill slits, and (4) a post-anal tail. In non-chordates all four are absent. Memorise the four together because NEET builds statement-matching questions around them.
In chordates the nerve cord is dorsal (on the back), hollow, and single. In non-chordates the nerve cord is ventral (on the belly side), solid, and double. NTA loves swapping these words, so read every option slowly.
Careful: the heart position is the OPPOSITE of the nerve cord. In chordates the heart is ventral (on the belly side). In non-chordates the heart is dorsal, if a heart is present at all. So chordate = nerve cord up, heart down. This flip is a classic NEET trap.
No. All non-chordates are invertebrates (no backbone), but not all chordates are vertebrates. Some chordates (Urochordata and Cephalochordata, the protochordates) have a notochord but never form a vertebral column, so they are chordates yet still lack a backbone. Only the subphylum Vertebrata has a true backbone.
No, true chordate pharyngeal gill slits are absent in non-chordates. This is why the 2024 NEET statement 'Pharynx is perforated by gill slits' was marked WRONG for non-chordates. (Hemichordata has gill slits and is a borderline case, but in the strict chordate/non-chordate table gill slits belong to chordates.)
Porifera, Coelenterata (Cnidaria), Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata. NCERT says non-chordates run 'from Porifera to Echinoderms.' Everything after that (Chordata) has the notochord.
The following are the statements about non-chordates: A. Pharynx is perforated by gill slits. B. Notochord is absent. C. Central nervous system is dorsal. D. Heart is dorsal if present. E. Post anal tail is absent. Choose the most appropriate answer.
Select the correct statements with reference to chordates. A. Presence of a mid-dorsal, solid and double nerve cord. B. Presence of closed circulatory system. C. Presence of paired pharyngeal gill slits. D. Presence of dorsal heart. E. Triploblastic pseudocoelomate animals.
Which of the following is not a characteristic of chordates?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Chordates: notochord present, nerve cord dorsal/hollow/single, gill slits present, post-anal tail present, heart ventral. Non-chordates: notochord absent, nerve cord ventral/solid/double, gill slits absent, no post-anal tail, heart dorsal if present.
Not always. NCERT says the features are present 'at some stage.' For example, the notochord may appear only in the embryo or larva. In vertebrates it is replaced by the vertebral column in the adult.
No. A notochord is a soft, flexible rod. A backbone (vertebral column) is made of bone or cartilage and forms only in vertebrates, often replacing the notochord. So a notochord is present in ALL chordates, but a backbone is not.
Because the positions are opposite in the two groups and are easy to swap in a fake option. Chordate = nerve cord dorsal (up), heart ventral (down). Non-chordate = the reverse. Remembering this flip protects you from trick statements.
