What is "gastrula"

Planula \Plan"u*la\, n.; pl. Planul[ae]. [L., a little plane.]

1. (Biol.) In embryonic development, a vesicle filled with fluid, formed from the morula by the divergence of its cells in such a manner as to give rise to a central space, around which the cells arrange themselves as an envelope; an embryonic form intermediate between the morula and gastrula. Sometimes used as synonymous with gastrula.

2. (Zo["o]l.) The very young, free-swimming larva of the c[oe]lenterates. It usually has a flattened oval or oblong form, and is entirely covered with cilia.

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

n. (context embryology English) A stage in the development of embryos of most animals consisting of a two-layered sac of ectoderm and endoderm.

1. n. double-walled stage of the embryo resulting from invagination of the blastula; the outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm

2. [also: gastrulae (pl)]