Fig. 8. Comparison of larvacean and vertebrate placodes. An Oikopleura early hatchling and a representative vertebrate embryo (24-hour zebrafish) are schematized in dorsal view to show the correspondence in topography between the larvacean ventral organ (VO) and vertebrate olfactory (OL) placodes (green), and between the ciliary funnel (CF) and adenohypophyseal (AD) placodes (yellow). The larvacean Langerhans (LA) and vertebrate otic (OT) placodes (blue) may also be orthologous, or they could have evolved independently from a common mechanosensory placode precursor. The larvacean ciliated circumoral mechanosensory organ (CO, orange), however, might be homologous to ascidian and cephalochordate oral mechanosensory systems, but might have no counterpart in modern vertebrates. FB, forebrain; HB, hindbrain; no, notochord; sc, spinal cord.