surrounded by surrounded by Danio rerio blastocele http://upload.wikimedia.org/wikipedia/commons/c/c3/Blastocyst.gif https://github.com/obophenotype/uberon/issues/475 blastocoelic cavity blastocoele SCTID:361455006 XAO:0000294 blastocyst cavity Wikipedia:Blastocele VHOG:0000811 UBERON:0000090 segmentation cavity EHDAA2:0000175 EMAPA:16044 cleavage cavity EHDAA:50 A blastocoel forms during embryogenesis when a zygote (a fertilized ovum) divides into many cells through mitosis. The blastocoel is the cavity of the blastula, a closed space which is invaded by early mesenchyme and later obliterated by the enlarging archenteron.[AAO] Fluid-filled central region of a blastocyst. blastocoel In the development of many animals, a hollow blastula stage is formed during early embryogenesis. Such a hollow blastula is even regarded as an autapomorphy of Metazoa and is present already in some sponges.[well established][VHOG] The cavity inside the blastula. [The_evolution_of_organ_systems_(2007)_Oxford:_Oxford_University_Press, p.150, see_Schmidt-Rhaesa_A][VHOG] AAO:0010433 blastocelic cavity FMA:293131 epiblast (generic) anatomical cavity