Blastulation is the stage in early animal embryonic development that produces the blastula. In mammalian development the blastula develops into the blastocyst with a differentiated inner cell mass and an outer trophectoderm. The blastula is a hollow sphere of cells known as blastomeres surrounding an inner fluid-filled cavity called the blastocoel. Embryonic development begins with a sperm fertilizing an egg cell to become a zygote, which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoel is formed does the early embryo become a blastula. The blastula precedes the formation of the gastrula in which the germ layers of the embryo form.
A. Morula and B. cross section of a blastula displaying the blastocoel and blastoderm of early animal embryonic development
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia, With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Animals form a clade, meaning that they arose from a single common ancestor.
Sexual reproduction is nearly universal in animals, such as these dragonflies.
Predators, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.
Hydrothermal vent mussels and shrimps
The blue whale is the largest animal that has ever lived.
