The middle germ layer of the embryo, between the endoderm and ectoderm.

http://upload.wikimedia.org/wikipedia/commons/e/e8/Mesoderm.png

Primary germ layer that is the middle of the embryonic germ layers.[AAO]

UBERON:0003263

uberon

embryonic mesoderm, mesodermal mantle, entire mesoderm

mesodermal

The Bilateria are triploblastic (with true endoderm, mesoderm, and ectoderm) (...).[well established][VHOG]

UBERON:0000926

http://purl.obolibrary.org/obo/uberon.owl, http://purl.obolibrary.org/obo/cl.owl

http://purl.obolibrary.org/obo/NCBITaxon_6040

sponges do not seem to have a mesoderm and accordingly Amphimedon lacks transcription factors involved in mesoderm development (Fkh, Gsc, Twist, Snail)[http://www.nature.com/nature/journal/v466/n7307/full/nature09201.html]. Mesoderm may not be homologous across verteberates

• axial mesoderm
• intermediate mesoderm
• mesoderm-derived structure

• mesoderm development

• mesoderm formation

• primitive streak
• presumptive mesoderm

• mesoderm morphogenesis

• musculoskeletal system
• presumptive gut
• entire embryonic mesenchyme

• future coelemic cavity lumen
• lateral plate mesoderm
• axial mesoderm
• intermediate mesoderm
• mesodermal cell