Question

Assertion
In Balanoglossus notochord is replaced by Pygochord.
Reason
Pygochord supports the abdominal region.
(А) both the assertion and the reason are true and the reason is a correct explanation of the assertion
(B) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(С) If the assertion is true but the reason is false
(D) If both the assertion and reason are false

Answer 1

Hint: Balanoglossus belongs to the kingdom hemichordate. The Name Hemichordate (Greek, hemi-half, ChordeCord) can be said and means that they are 'half chordates, a fact that is undisputed. This kingdom consists of worm-like animals.

Complete answer:
The name hemichordates was derived based on the structure present in their body which was considered to be their notochord'. But this fact is no longer supported. So now hemichordates are considered non-chordate that do not have notochord that is supporting structure.
In balanoglossus there is no endoskeleton but there are some supportive structures present in this :-
> Buccal Diverticulum :-
It is a hollow pre oral growth. It usually extends from the roof of buccal cavity till the proboscis. It was earlier assumed to be the notochord or stomochord because it represents the anterior portion. It is not homologous and nor analogous to the notochord but is similar to buccal cavity.
> Proboscis skeleton :-
It is also called a nuchal skeleton. It is formed by basement membrane. Basement membrane becomes thick to become a laminated plate. It has a midventral keel.
> Branchial skeleton :-
The walls of U-shaped gill slits are usually supported by a structure that is made from basement membrane and this structure is known as a branchial skeleton.
> Pygochord :-
Pygochord is a longitudinal structure. It is tube like structure and it extends from the ventral side of the intestine to the body wall. It supports the abdominal region.
As notochord is not present in balanoglossus, assertion is false and pygochord extends to body wall and not abdominal wall so reason is also false.

Our required option is D. If both the assertion and reason are false.

Note:
Balanoglossus is a "ciliary feeder" (or filter-feeder). The food of balanoglossus is made up of microscopic organisms and organic particles present in water and bottom sand in oceans in which it makes its burrows. The food particles enter the body through the gill-slits (pores in the pharynx).
These food particles are then filtered by the cilia lining the gill-slits.