gas·tru·la 
(găstrə-lə)
(găstrə-lə)n. pl. gas·tru·las or gas·tru·lae (-lē′)
An embryo at the stage following the blastula, after the movement of cells results in the formation of the three germ layers, ectoderm, mesoderm, and endoderm.
[New Latin : Greek gastēr, gastr-, belly + Latin -ula, feminine diminutive suff.]
gastru·lar (-lər) adj.