Question

What is the characteristic of the notochord in Cephalochordate?
A) It extends along the length of the body.
B) It is restricted to the head region.
C) It is restricted to the body excluding the head region.
D) It is present along the length in larva but restricted to head in adults.

Answer 1

Notochord is the cartilaginous skeleton rod that supports the body in the embryonic and adult chordates. It serves the purpose of providing mechanical and signalling support to the animals. The Cephalochordates is the subphylum of chordates but have a dorsal nerve cord and notochord. The notochord provides support to the cephalochordates.

Complete answer:
The cephalochordates are marine organisms that have a notochord, dorsal and hollow nerve cord, pharyngeal gill slits. They have notochords that are not replaced in adulthood.

The characteristics of the Cephalochordata notochord are:
- The cephalochordates have the notochord which runs throughout the body from head to tail of the organism. (Statement A is correct).
- The muscle fibres help in maintaining the stiffness of the notochord. The nerve cord has a firm sheath along with the core that is made up of cells that contain muscle fibres. It prevents shortening of the body during swimming. The support is also provided by the gills, fins, and cirri which contain stiff and supportive rods.
- The notochord persists in the organism throughout life and is not replaced by vertebrae.

In the case of vertebrates, the notochord which is present in the embryonic stage is replaced by the vertebrae made up of bones or cartilage but in the case of cephalochordates, the notochord is retained in the adults and is not replaced by vertebrae. (Statement D is incorrect)

The notochord which runs in the body except the head is the characteristic feature of urochordates. Example Tunicates (Statement C is incorrect).

Thus, the correct answer is A.

Note: Cephalochordates like lancelet serve as a good source of food and plays an important role in the food chain. These organisms do not show asexual reproduction as the sexes are separate. They do not have cranium hence they are called acraniates.