Figure 2

Various components of the juvenile nervous system of N. arenaceodentata. Acetylated α-tubulin immunoreactivity is red; cell nuclei are blue. Scale bars = 100 μm in A, B, G, J, K; 50 μm in C, H, I; 25 μm in D-F. A. Hatchling; ventral view, anterior to the top. Segmental nerves 1 and 4 are visible within the dashed box. B. 5-chaetiger juvenile; ventral view, anterior to the upper right. Arrows point to the first (medial-most) pair of stomatogastric nerves. C. 9-chaetiger juvenile; ventrolateral view between chaetigers 5 and 6, anterior to the left. Numerals 1-4 refer to segmental nerves 1-4. Dashed circles and dashed boxes enclose regions expected to contain nerve interconnections described in the text. Dashed green ellipses represent parapodial ganglia; closed double arrowheads point to axons of the sn2/4 interconnection; dots are positioned near the bases of the four main parapodial nerve branches, pn1-4 (in order from anterior to posterior); and open double arrowheads point to nerves with uncertain dorsal termini. D-F. Contiguous Z-projections of the dorsal portion of a 9-chaetiger juvenile's pharynx, anterior to the top. D. Dorsal-most Z-projection (above the pharyngeal lumen). Arrows point to commissural nerves, and punctate labeling probably represents innervation of pharyngeal muscle. E. Middle Z-projection. Brackets contain regions of the main dorsal pharyngeal nerves that show fine neurite connections to cells of presumed ganglia. The dashed line separates the pharynx from the esophagus. F. Ventral-most Z-projection. Arrows point to the bases of the developing jaws, the tips of which are outlined for clarity. G. 12-chaetiger juvenile anterior end; ventral view, anterior to the top. Arrows point to stomatogastric nerves 1-5 (anterior to posterior). H. Anterior cirri of a 12-chaetiger juvenile (left side of head). The anterodorsal cirrus is at the bottom of the panel; the posterodorsal cirrus is above the latter. I. Anal cirri of an 8-chaetiger juvenile; ventral view. J, K. 20-chaetiger juvenile; ventral view, anterior to the top. J. Mid-body segments. A single pair of VNC ganglia is boxed, and an arrow points to its pre-septal portion. Dashed green lines delimit a single segment. All other labeling (zoom in to see) follows panel C. K. Posterior end. 1st/2nd nascent parapodia, ag antennal ganglion, an antenna, ana anal cirrus, ant anterior cirrus, br brain, cc circumesophageal connective, cn cirrus nerve, dpn dorsal pharyngeal nerve, irc immunoreactive cell, mln median longitudinal nerve of the vnc, ne nephridium, npw nerve of palp wall, pa palp, pn axial palp nerve, rcc root of the circumesophageal connective, sc sensory cilia, sn2 segmental nerve 2, st stomodeum, vnc ventral nerve cord.