2 public questions tagged with this topic.
In Urochordates (e.g., Ascidia), the notochord is present only in the larval stage, whereas in Cephalochordates (e.g., Branchiostoma), it is present throughout life.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Hemichordata and Chordata - Protochordata
Subphylum Urochordata, synonymous with Tunicata, includes marine filter feeders like Herdmania, Ciona, Salpa, Doliolum and Pyrosoma encased in secreted tunic composed of tunicin resembling cellulose. Adults are sessile, sac-like with incurrent and excurrent siphons, lacking notochord, dorsal nerve cord and segmented muscles due to retrogressive metamorphosis where tail resorbed. Free-swimming tadpole larva retains chordate features for dispersal. Cephalochordata contains Branchiostoma amphioxus, Agnatha contains lampreys, Chondrichthyes sharks and bony fishes. Tunicate classification emphasizes loss of chordate traits in adult demonstrating developmental plasticity within protochordates.
Ref: NCERT Class 11 Biology, Chapter 4: Protochordata – Urochordata; Brusca & Brusca, Chapter 23, Tunicates
