Question

In which of the following notochords is present in the embryonic stage?
A. All chordates
B. Some chordates
C. Vertebrates
D. Non-chordates

Answer 1

The notochord is located on the back wall of the intestine of the embryo. It is located below and above the central nervous system. It is a derivative of mesoderm .The notochord nucleus consists of fluid-filled cells and vacuoles. The outer surface surrounding the underlying tissue is a tough fibrous sheath of connective tissue. This structure provides support.

Complete answer:
The phylum Chordata includes a large group of different animals .Different characteristics such as notochord, spinal cord hollow tubular nerves, and pharyngeal gill slits unite these different animals under the same type.
Chordata: The phylum Chordata includes a large group of different animals, from ascidians to humans. Different characteristics such as notochord, spinal cord hollow tubular nerves, and pharyngeal gill slits unite these different animals under the same type.
Hemichordata provides an overview of the relationship between chordates and non chordates.
Division of Chordata:
Subphylum Cephalochordata
Subphylum Urochordata
Subphylum Vertebrata (Craniata)

Urochordata: This subtype is also known as a tunicate because an adult's body is caught in a skin test or tunic made from an organic substance called cellulose called tunicin. The notochord exists only in the tail of the larva and disappears as an adult. The dorsal tubular nerve cord is located inside the larva. It is replaced by the dorsal ganglion in adults. Urochordates have an open circulatory system.
Cephalochordata- Both adults and larvae are motile. The notochord extends to the front end of the body. The notochord is preserved throughout life. More and better developed pharyngeal gill slits. Atria are also present. The tail exists throughout life. Cephalochordates have a closed circulatory system. The members of this phylum are ciliary feeders

Let’s summarise all the points above to answer the given question
Hemichordates have long been considered the lowest group of Chordata that make up the notochord, nerve cord, and pharyngeal gill slits, the main feature of the phylum chordata. Modern workers claim that the notochord of the half-chord data is not an actual notochord, and that the central nervous system, which contains longitudinal ventral nerve chains, exhibits characteristics of the major invertebrate phyla.
In Urochordates larva shows retrogressive metamorphosis .
Notochord does not exist at any stage in the life of an Non-chordates. The central nervous system is tough and stiff. Branchial cleft and tail is also absent. Heart is dorsal in position. If haemoglobin or other respiratory pigments are present, they are in the plasma.
The notochord is the basic identifying structure of the chordates, the group gets its name due to this reason.

Hence the correct option is (A).

Note: Stomochord instead of notochord is present in non chordates. The Stomochord looks like the outer pocket of the roof of the embryonic colon in front of the pharynx. It is derived from Endoderm. There is a narrow lumen opening in the pharynx. The lumen wall consists of a long, very narrow layer of cells containing dense intracellular vacuoles. The outer surface is composed of ciliated cells as well as epithelial cells such as the oral cavity. The structure does not provide support. It mainly helps in the movement.