Does chicken embryo form the disc called "discoblast" in the cleavage and blastulation of chicken?
It is a mnemonic of two words: discoidal + blastula = discoblastula.
So it suggests that cleavage is partial discoidal in birds.
Embryo forms disc. 
Cells called blastodisc are on top of the yolk.
It seems that the formed disc is blastodisc.