Question

significance of larval forms of protochordates in phylogenetic studies of chordates . for 7 mark​

Answer 1

Explanation:

In urochordates, the notochord is present in larval stages and later gets degenerate but in cephalochordates it is present along the entire length of their body during their complete life.Notochord is a long flexible rod like structure present in all chordates which separates the nervous system from the gut.

Answer 2

The significance of larval forms of protochordates in phylogenetic studies of chordates is that they exhibit all the essential characters possesed by chordates.

Explanation:

The Subphyla Urochordata and Cephalochordata are reffered to as Protochordata ( proto- primitive ) or Acrania ( without cranium or the brain box). The larval form of these animals show all the features which are essential for that organism to be classified under Phylum Chordata. The diagnotic characters of of the animals in Phylum Chordata  are -

1. Notochord - it is the solid unjointed stiff but flexible rod-like structure situated on the dorsal side of these animals. In higher vertebrates, this structure forms the backbone or vertebrata.
2. Dorsal Hollow Nerve Chord - Just below the dorsal skin, above the notochord, a hollow nerve chord is present. In higher animals, this forms the spinal chord.
3. Pharyngeal Gill Slits - At some stage of life of all chordates, they possess a series of paired narrow openings, the gill slits on the lateral sides of the pharynx.
4. Tail - It is the post-anal extension of the vertebral column which is absent or reduced in many adult chordates.  

All these features will be expressed by all chordates in some stage of their life.