part of start stage end stage diencephalon epithalamus Brain structure which is part of the diencephalon and consists of the dorsal and ventral nuclei of the habenula, and two dorsal outgrowths, the epiphysis and the saccus dorsalis. From Neuroanatomy of the Zebrafish Brain. zebrafish_anatomy TAO:0000509 ZFA:0000509 multi-tissue structure segmentation:10-13 somites adult