dc:description"Fig. 2 Neurogenesis in metamorphosing stages of B. misakiensis. b, c, e–k Z-projections of confocal microscopy image stacks. a, d Scanning electron micrographs. Anterior is to the top. a SEM of early metamorphosing stage (Spengel) from lateral left. Arrowhead points to the dorsolateral slit-like depression. b Overview of the serotonin-LIR nervous system (NS) in Spengel stage, view from left. Numerous serotonin-LIR neurons are part of the apical organ. Note the serotonin-LIR opisthotroch neurite ring. c Overview of the serotonin-LIR NS of a late metamorphosing stage (Agassiz), dorsal view. d Dorsal view of metamorphosing Agassiz stage. e Detail showing the developing 5-HT+ nervous plexus in the postoral region of the Spengel stage. f Close-up of the 5-HT+ apical organ";
dc:description"Fig. 3 Ultrastructural details of the developing nervous system Balanoglossus misakiensis. a Sagittal section of an Agassiz stage larva of B. misakiensis. b Sagittal section of a 2-gill-slit juvenile of B. misakiensis.c Ultrastructural detail of the red-marked box in a showing a continuous layer of neurites of 4–6-μm thickness in the Agassiz stage. Inset color-coded image of the micrograph shown in c. d Ultrastructural detail of the red-marked box in b showing only individual basiepidermal";
dc:description"Fig. 4 Neurogenesis in early settled stages of B. misakiensis. a, c–i, l, m Z-projections of confocal microscopy image stacks. b, k Scanning electron micrographs. a Ventrolateral overview of the serotonin-LIR NS of an early settled juvenile. Anterior is to the left. b Left side view of early settled juvenile. c Detail of the anterior trunk region of early settled juvenile showing a ubiquitous basiepidermal nervous plexus. d Partial Z-projection showing the longitudinally orientated neurites within the collar region. e Detail of the 5-HT+ proboscis plexus at the base of the proboscis and the neurite bundles passing through the subepidermal collar cord. f, g Close-up of the gill pore and mesocoelic pore showing the prebranchial nerve ring and the nervous plexus entangling the mesocoelic duct in f. h SEM of a settled juvenile in lateral right view. i Close-up of the apical tip of the proboscis. k Detail of the dorsolateral collar region showing two clusters of 5-HT+ bipolar neurons that encircle the collar. l Overview of the 5-HT+ NS of a settled juvenile 24-h postsettlement, lateral right view. m Detail showing circular 5-HT+ neurites within the posterior part of the trunk whereas more anterior a net-like pattern is still present. The apical tuft and cluster of 5-HT+ somata has disappeared. Apical is to the top. 5-HT, serotonin; ac-α-tub, acetylated α-tubulin; a, anus; ao, apical organ; cgn, ciliary groove nerves; cn, circumferential neurite; cc, collar cord; co, collar; gs, gill slit; mcb, middle circular neurite bundle; msp, mesocoel pore; ne, neurite; nn, nervous plexus; onr, opisthotroch nerve ring; pnr, prebranchial nerve ring; pr, proboscis; ps, proboscis stem; sn, serotonin-LIR neuron; tr, trunk; vnb, ventral neurite bundle";
dc:description"Fig. 5 Neurogenesis in the 2-gill slit juvenile of B. misakiensis. a, b Scanning electron micrographs: c–i Z-projections of confocal microscopy image stacks. Anterior is to the right. a Dorsolateral view of a 3-day-old settled juvenile. b Higher magnification of the two gill slits and the dorsal tongue bars. c Overview of the 5-HT+ NS of a 3-day-old juvenile. d The collar cord is composed of three 5-HT+ neurite bundles of which the median one projects posteriorly into the dorsal nerve cord. e Detail of the ventral 5-HT+ neurite bundle with numerous incoming circular neurites emerging from lateral bipolar neurons. f Detail of the anterior part of the dorsal 5-HT+ neurite bundle and epidermal collar region. This part is discontinuous with the posterior part of the 5- HT neurite bundle shown in g, see also double arrowheads and dashed area. g The posterior part of the dorsal 5-HT+ neurite bundle contains few serotonin-LIR neurites and is discontinuous with the anterior part of the 5- HT neurite bundle, see double arrowheads and dashed area. h Partial Zprojection of a sagittal scan of the dorsal collar region. The collar cord comprises ventral neurite bundles and a dorsal sheath of somata, which are not serotonin-LIR positive. i Close-up of a part of the proboscis region showing the 5-HT+ bipolar neurons and the basiepidermal nervous plexus. 5-HT, serotonin; a, anus; ac-α-tub, acetylated α-tubulin; cn, circumferential neurite; cc, collar cord; ci, cilia; co, collar; dnb, dorsal neurite bundle; ep, epidermis; gs, gill slit; msp, mesocoel pore; nn, nervous plexus; onr, opisthotroch nerve ring; pnr, prebranchial nerve ring; pr, proboscis; ps, proboscis stem; sn, serotonin-LIR neuron; tb, tongue bar; tm, trunk musculature; vnb, ventral neurite bundle";
