gastraea
/ɡæˈstriːə/
noun
- A hypothetical ancestral form of all multicellular animals, proposed by Ernst Haeckel, resembling a two-layered sac with a mouth.
- Haeckel's theory of the gastraea was influential in early evolutionary biology.
- Students of zoology often study the concept of the gastraea to understand animal development.
- The gastraea is thought to be the common ancestor of all eumetazoans.