gastrula

< /ˈgæs trʊˌli/. Embryology.

1. a metazoan embryo in an early state of germ layer formation following the blastula stage, consisting of a cuplike body of two layers of cells, the ectoderm and endoderm, enclosing a central cavity, or archenteron, that opens to the outside by the blastopore: in most animals progressing to the formation of a third cell layer, the mesoderm.

noun plural -las or -lae (-ˌliː)

1. a saclike animal embryo consisting of three layers of cells (ectoderm, mesoderm, and endoderm) surrounding a central cavity (archenteron) with a small opening (blastopore) to the exteriorSee also ectoderm, mesoderm, endoderm

n.

1877, Modern Latin, from Greek gaster (genitive gastros) “stomach” (see gastric) + Latin -ula, diminutive suffix. Related: Gastrulation.

n. pl. gas•tru•las

1. An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore.

Plural gastrulas gastrulae (găs′trə-lē′)

1. An animal embryo at the stage following the blastula. The gastrula develops from the blastula by invagination (inpocketing), forming an inner cavity with an opening and causing the cells to be distributed into an outer layer (ectoderm) and an inner layer (endoderm). In complex animals such as vertebrates, a third layer (mesoderm) also forms. These layers later develop into the organs and tissues of the body. In vertebrates and other deuterostomes, the opening of the gastrula becomes the anus, while in protostomes (such as arthropods), it becomes the mouth.♦ The development of an embryo from blastula to gastrula is called gastrulation. Compare blastula.