Gastræa

gas-trē′a, n. ( biol. ) a hypothetic animal form a umed by Hæckel as the ancestor of all metazoic animals:— pl. Gastræ′æ .— n. Gas′trula , that embryonic form of metazoic animals which consists of a two-layered sac enclosing a central cavity and having an opening at one end:— pl. Gras′trulæ .— adj. Gas′trular .