Question

All chordates at one or other stage possess
A. Vertebral column
B. Pharyngeal gill-slits
C. Two pairs of pentadactyl limb
D. A movable jaw

Answer 1

Hint: In the Kingdom Animalia of the five kingdom classification system, there are many phylums. Out of these phylum one is called a phylum chordata that includes two groups- lower chordates (protochordata) and higher chordates (euchordata).
Under euchordata, there is a subphylum called vertebrata. These vertebrates are further divided into two divisions- agnatha (jawless animals) and gnathostomata (jawed animals).
Under gnathostomata, there are two super classes -one is pisces (fishes) and the other is tetrapoda. Tetrapoda includes classes like amphibia, reptilia, aves and mammalia.

Complete answer: Chordates are animals which have a thick string-like structure that is present called a notochord in any stage of their life span. Notochord is a solid rod-like structure present just below the nerve cord and above the alimentary canal during the embryonic stage of the animal.
In protochordates, notochord is not replaced by vertebral column but in vertebrates, it is replaced by backbone or vertebral column in adults.
Thus the vertebral column is not seen in all Chordates but notochord is present in all Chordates.
The number of digits in the limbs of each chordate differs from other. Some chordates do not have digits in their limbs (digitless limbs are found in many aquatic chordates). Some have four to five digits in their limbs. Thus pentadactyl limbs (having five digits) are not found in each chordate.
Chordates of division Agnatha do not have jaws (jawless animals) whereas chordates of division Gnathostomata contain jaws (jawed animals).
Thus the presence of a movable jaw is not a characteristic feature of all chordates.
In each chordate, there are present paired lateral gill clefts in the walls of pharynx for respiration in any stage of its life span.
In aquatic chordates and lower chordates, pharyngeal gill clefts are present throughout their life span for respiration but in terrestrial chordates, gill clefts are found only in embryonic stage and are absent in adults. Thus presence of pharyngeal gill slits is the characteristic feature of all chordates.
So, the correct answer is “Option B”.

Note:
Apart from the presence of notochord and paired pharyngeal gill slits, all chordates have a dorsal hollow nerve cord and a post anal tail in some stage of their life span. Central nervous system of chordates is dorsal, hollow and single and also the heart is present ventrally. According to taxonomists, non-chordates are majorly found on earth as compared to chordates.