specialized extracellular matrix embryonic sheath https://github.com/geneontology/go-ontology/issues/31680 2026-03-06T09:07:34Z pg cellular_component A specialized, transient apical extracellular matrix (aECM) that overlays the apical surface of the embryonic epidermis in Caenorhabditis elegans. It is secreted just prior to the start of embryonic elongation and acts as a mechanical scaffold to maintain embryonic integrity, distribute actomyosin-dependent stress, and anchor developing muscles. GO:0140400