Pronunciation: GAS-tru-la

Etymology: It is the Latin diminutive (diminutive ending -ula) of a Greek root, gaster (γαστήρ), which means belly, stomach, or womb. Thus, gastrula literally means “little belly” and is a reference to the invagination of the blastula forming the archenteron, the first stomach (see below).

The gastrula is a ball of cells that develops from the blastula. It is initiated by the formation of the blastopore that can develop into a complete food tube or become arrested as a gastrovascular cavity. The gastrula also is the point at which the embryo forms two cell layers (in the Radiata) or three cell layers in the Bilateria (Prototostomata and Deuterostomata).