part of part of develops from develops from Eumetazoa pectoral fin multi-tissue structure fin fold pectoral fin bud pectoral fin fold pectoral fin-fold UBERON:2005317 ZFA:0005317 This class was sourced from an external ontology (teleost_anatomy). Its definitions, naming conventions and relationships may need to be checked for compatibility with uberon The functional webs of the paired fins. They arise as a consequence of apical fold (AER) expansion and of migration of the distal mesenchyme. The fin folds are delimited by a dorsal and a ventral striated epidermis. The cells of the epidermal basal stratum are positioned on a basement membrane. Directly beneath the basement membrane of each side there is an array of actinotrichs, fibers of the extracellular matrix which act as supportive elements of the larval fin folds.