Question

The type of blastula formed in birds is
(a) Teloblastula
(b) Holoblastula
(c) Coeloblastula
(d) Discoblastula

Answer 1

Hint: This blastula is the result of meroblastic discoidal cleavage as in most fishes, reptiles, and birds. The hollow sphere of cells surrounding an inner fluid-filled cavity formed during an early stage of embryonic development in animals is called the blastula.

Complete step by step answer:
The type of blastula formed in birds is Discoblastula. A blastula formed from the partial cleavage that occurs in the fertilized ovum containing a large amount of yolk is called Discoblastula. It develops from the blastodisc and consists of a cellular cap, or blastoderm, separated from the uncleaved yolk mass by a small cavity, the blastocoel. This type of cleavage is seen in reptiles and birds.
So the correct answer is ‘Discoblastula’.

Additional information:
- Coeloblastula is a blastula formed as a result of complete holoblastic cleavage. It is formed in echinoderms and Amphioxus.
- Holoblastula is a type of cleavage which is normally seen in eggs having a modest to the light amount of yolk. It is formed in amphibians, echinoderms, and mammals.
- Superficial blastula is one that shows the absence of blastula and is formed as a result of superficial cleavage.
- Amphiblastula is formed in amphibians as a result of two structurally different blastomeres.
The blastula of various groups of animals differs in form and structure depending upon a variety of factors such as the size of the amount and distribution of yolk etc.
It precedes the formation of gastrula in which germ layers of the embryo form.

Note:
- Discoblastula consists of a disc- shaped mass of blastomeres overlaying a large yolk mass. Blastocoel is absent instead a slit- like cavity called a subgerminal cavity appears in between the blastoderm and the yolk mass.
- Embryo development begins with a sperm fertilizing an egg to become a zygote, which undergoes many cleavages to develop into a ball of cells called a morula. After the formation of blastocoel, the early embryo becomes a blastula.