Name: very early blastula stage
ECAO ID: 0000250
Definition: "The embryo is composed of 110-120 cells, as most blastomeres have completed an additional mitotic division after the 60-cell stage. The embryo is surrounded by a fertilization envelope. All cells are about the same size and there are no obvious morphological indications of embryonic polarity or embryonic territories. All cells have begun to acquire apico-basal polarity, and the embryo is beginning to transform into a hollow sphere with a wall that is one cell layer thick and a fluid-filled cavity (the blastocoel) in the center. Note for euechinoid indirect developers: the micromere progeny divide more slowly than other cells of the embryo. Molecular labelling typically indicates the presence of 8 large micromere descendants and 4 small micromeres at this stage ."