part of develops from start stage end stage pectoral fin multi-tissue structure fin fold pectoral fin bud pectoral fin fold zebrafish_anatomy Ceri pectoral fin membrane TAO:0005317 2010-02-10T03:27:29Z ZFA:0005317 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. hatching:pec-fin adult