To which group does $Salpa$ belong?

The animal group,where the adults are degenerated but larvae are well developed,is

Which of the following statements is/are correct for the phylum Chordata?
$(a)$ In Cephalochordata,the notochord extends from head to tail region and is persistent throughout their life.
$(b)$ In Vertebrata,the notochord is present only during the embryonic period.
$(c)$ The central nervous system is dorsal and hollow.
$(d)$ Chordata is divided into $3$ subphyla: Hemichordata,Urochordata,and Cephalochordata.

All chordates at one or the other stage possess

$A$ rabbit shows resemblance with a frog in which of the following features?

All of the following are characteristics of urochordates,except: