part of part of develops_from external ectoderm simple squamous epithelium integument periderm A temporary epithelium that derives from the outer layer of the ectdoerm and is shed once the inner layer differentiates to form a true epidermis. EHDAA2:0001846 EHDAA:6538 EVL FMA:295662 In mice, the first non-basal layer formed at ~E9.5; it is a temporary structure composed of simple squamous epithelium that serves as the first barrier to the embryo's physical environment, exists throughout the entire keratinocyte stratification process, and sheds off at ~E17, when it is replaced by corneocytes[MP] In some mammals, Eyelid Fusion is thought to be driven by a population of cells which are derived from the periderm, the outermost layer of the developing epidermis Originally the epidermis is one layer thick, in most vertebrates it soon becomes a two-layered structure. The outer layer gives rise to the periderm. The periderm goes through distinct developmental phases and is ultimately sloughed into the amniotic fluid when differentiation of the underlying epidermal layers is complete. The function of the periderm is not known, but is thought to be related to transport/exchange between the fetus and the amniotic fluid (http://courses.washington.edu/hubio567/devbio/periderm.html) TAO:0001185 The outermost epidermal layer covering the fish at embryonic stages; derived from the EVL and thought to eventually be replaced by the superficial stratum of the epidermis. Sometimes used synonymously with EVL. Le Guellec et al, 2004.[TAO] UBERON:0003055 UMLS:C1518973 VHOG:0001680 XAO:0000029 ZFA:0001185 epidermis epithelial layer epidermis outer layer epitrichium periderm relationship type change: OBO_REL:part_of ectoderm (TAO:0000016) CHANGED TO: develops_from ectoderm (UBERON:0000924)[TAO] skin periderm uberon enveloping layer of ectoderm ecto-epithelium