Which of the following is not a subphylum of Chordata?

Which one feature is common to $Amphioxus$,frog,sea horse,and crocodile?

One of the primary characteristics of chordates is:

Which of the following is the smallest taxonomic group of animals having a cranium,vertebral column,ventral heart,pulmonary respiration,and two pairs of limbs?

Which of the following statements is true?

Identify the animals belonging to Urochordata (Tunicata) and Cephalochordata,respectively.
Urochordata $\quad$ Cephalochordata