abnormal somite development abnormal somite segmentation MP:0001688 MPheno.ontology abnormal metablastic segment development abnormal somite formation abnormal somitogenesis any anomaly in the formation of mesodermal clusters that are arranged segmentally along the anterior posterior axis of an embryo; somites are transient structures - balls or blocks of paraxial mesoderm cells with an epithelial outer layer and a mesenchymal cell core - that emerge sequentially through a mesenchymal-to-epithelial transition (MET) from the morphologically unpatterned presomitic mesoderm; they give rise to the metameric anatomy of the vertebral column itself, and the associated skin, muscle and tendons abnormal embryonic tissue morphology