Question

All vertebrates are chordates but all chordates are not vertebrates. Justify the statement.

Answer 1

Chordata is the most advanced animal phylum that includes about 45,000 living species. They are bilaterally symmetrical, triploblastic animals with organ-system level of organization and metamerism. They also have closed circulation and special respiratory and excretory organs.

Complete answer: All the chordates have certain diagnostic features like
Presence of notochords- Notochords are a solid and unjointed mesodermal rod of vacuolated cells on the dorsal side between the alimentary canal and nervous system. It acts as a primary axial skeleton and is surrounded by a notochordal sheath.
The dorsal and hollow central nervous system that is differentiated into anterior broader brain and posterior narrow spinal cord. It lies dorsal to the notochord.
Gill slits are paired apertures present on the lateral side of the pharynx that help in respiration.
They have a post-anal or post-cloacal or tail part of the body.
These four primary chordate characters are always present during embryonic development but maybe present throughout life in some. This phylum Chordata is divided into three subphyla on the basis of fate of notochord:
Urochordata- They have a notochord present only in the tail of larva which gets lost during metamorphosis, so the adult is tailless.
Cephalochordata- In these, the notochord extends from head to tail of the body so called cephalochordates. This notochord persists throughout life.
Vertebrata- In vertebrata, the notochord or chorda dorsalis is present during the embryonic period but s replaced by a rod of cartilaginous or bony rings, vertebrae and is called vertebral column or backbone, so called vertebrata.
This shows that all the vertebrates are chordates but all the chordates are not vertebrates.

Note: So, Chordates possess notochord at least in some stages of their life cycle. The subphylum veterbrata is also called craniata and it is divided into two subdivisions on the basis of jaws- Agnathostomata and Gnathostomata.