part of develops from start stage end stage pronephric mesoderm pronephros zebrafish_anatomy ZFA:0000151 embryonic kidney pronephric nephron TAO:0000151 The embryonic kidney, present at the level of the third somite, is composed of two glomeruli fused at the midline, two pronephric tubules, and paired bilateral pronephric ducts that modify the composition of the blood filtrate before delivering it to the cloaca for excretion. renal system cavitated compound organ pleuroperitoneal region segmentation:10-13 somites larval:days 7-13