diploblasticPronunciation: /ˌdɪplə(ʊ)ˈblastɪk/Definition of diploblastic adjective Zoology having a body derived from only two embryonic cell layers (ectoderm and endoderm, but no mesoderm), as in sponges and coelenterates. diploblastic in other Oxford dictionaries Definition of diploblastic in the US English dictionary