Figure 1

Schematic representation of an amphioxus early larva. The central nervous system (CNS) of an amphioxus early (36-hr) larva includes an anterior cerebral vesicle (CV), which, anteriorly, contains a frontal eye complex (FE) and, posteriorly, the infundibular organ (IO) as well as the lamellar body (LB). At the posterior end of the CV, there is a small midbrain-like region that includes the tectal zone extending from the posterior of the lamellar body to the anterior of the primary motor center (PMC). Posterior to the CV, the amphioxus CNS is divided into a hindbrain-like region, (extending from the posterior part of the PMC to the boundary of somites 7 and 8) and a territory corresponding to the vertebrate spinal cord. FB, forebrain; MB, midbrain; HB, hindbrain; SC, spinal cord; PS, first pigment spot; S, somite; N, notochord; M, mouth.