Blastulaa

Blastulaa appears to be a nonstandard or possibly misspelled term in embryology. The conventional term is blastula, an early stage of animal embryonic development that follows cleavage. It is typically a hollow sphere formed as blastomeres enclose a fluid-filled cavity called the blastocoel. The transition to the blastula follows the morula, a solid cluster of cells produced by successive mitotic divisions of the zygote. Cleavage patterns vary among groups; in many species the blastula forms after rapid holoblastic cleavage, while in others (notably birds and some reptiles) discoidal, meroblastic cleavage yields a disc-shaped blastoderm on top of yolk.

In mammals the blastula stage is represented by the blastocyst, which contains an inner cell mass that will form the embryo proper and an outer trophoblast that contributes to the placenta. Implantation into the uterine lining marks a key later step in mammalian development.

Gastrulation occurs after the blastula stage, reorganizing the cells into three germ layers—ectoderm, mesoderm, and endoderm—and establishing the body's primary axes. The blastula thus serves as a transitional waypoint between early embryonic cleaving and the more specialized phases of development during gastrulation and organogenesis.

In many texts, the plural of blastula is blastulae or blastulas. The term blastulaa is not standard in developmental biology and is likely a typographical error or a misused variant. If you intended blastula or blastulae, the above describes the conventional concept.