any structural anomaly of the anatomical surface separating somites; somite formation requires the physical separation of somitic tissue from the initially continuous presomitic mesoderm (PSM), coalescence of cells in the forming somite, and the establishment of a stable border between the somite and the PSM; when a somite forms in the anterior end of the PSM, an intersomitic boundary (also called a fissure, gap, or cleft) emerges, and it is rapidly followed by a mesenchymal-to-epithelial transition of cells that face a forming gap