(1) Pertaining to a condition (especially of a blastula or ovum) in which there is only one primary germ layer.
(2) Having developed from an embryo with only one germ layer.
Sea sponges are described to have been derived from a monoblastic embryo.
Word origin: Greek mono, single or alone + blastikós, budding.
Compare: triploblastic, diploblastic.
See also: blastula, germ layer.