Primary Germinal layer not present in diploblastic organisms-
Ectoderm
Mesoderm
Endoderm
Mesoglea
There are primarily 3 Germinal layers present in triploblastic organisms, i.e., Ectoderm, mesoderm, endoderm. But in diploblastic organisms only two layers are present which are Ectoderm and endoderm. And mesoglea is present between the cavity of Ectoderm and endoderm.
Option b is the correct answer.