Question

What is the difference between nonchordata & chordata?

Answer 1

Animals that have notochord are categorised into chordata.
Some chordates  like Ascidia, Salpa, Doliolum , etc  have a notochord, which is not present  at all stages in their lifecycle ( only at larval stages), nor does it run the entire length of an animal’s body.  . These chordates are grouped into sub group called Urochordata.
Some chordates  like Balanoglossus, Herdmania, Amphioxus, Saccoglossus etc have a notochord, which is present at all stages in their  life cycle, running from head to tail. These chordates are grouped into sub group called Cephalochordata.

Therefore, both these groups of animals are kept in a separate sub-phylum named Protochordata

Animals where the notochord is present only in embryological stages and later give rise to the vertebral column are called vertebrates.The members of sub-phylum Vertebrata under Phylum Chordata are advanced chordates that include animals belonging to classes- Pisces,Amphibia, Reptilia, Aves and Mammalia. 

Answer 2

1. Non-chordata heart if have on the dorsal side .

in chordata heart is present on the ventral side.

2.in non-chordata body is not supported by rod-like notochord.

in chordata body is supported by the notochord.

3.in Non-chordata nerve cord; if present is on the ventral side. it is solid and paired.

in chordata nerve cord is present is on the dorsal side. it is hallow.

4.Non-chordata pharyngeal gills-slits are abscent.

in chordata pharyngeal gills-slits or lungs are present for respiration