Figure 8
Organization of the serotonin-like immunoreactive nervous system in a 24-day-old larva. Micrographs of a live animal (A), Z-projections (B-I) of larvae after mono- and double staining with antibodies against 5-HT (serotonin) (green), as well as staining with phalloidin (grey), and Hoechst (violet), and 3-D reconstructions (J-K). (A) General view of a live larva showing the apical plate (ap), the border of the preoral coelom (bc1), vestibulum (v), esophagus (eso), stomach (st), midgut (mg), proctodaeum (pr), the border of the trunk coelom (bc3), tentacle (t), telotroch (tt), and primordium of the metasomal sac (pms). Lateral view; apical is to the top; ventral is to the right. (B) Nervous system with all major elements: apical organ (ao), median neurite bundle (men), frontal organ (fo), oral nerve ring (or), tentacular neurite bundle (tn) with dorsal commissure (dc), and nerve ring of the telotroch (nt). Lateral view; apical is to the top, ventral to the right. (C) Dorsal view of branched proximal ends of the tentacular neurite bundle (br) and apical organ, which is composed of monopolar (mo) and bipolar or multipolar perikarya. The latter forms the larger group on the left (lgn), which rises above the neuropil (np). Anterior is to the upper right. (D) Overview of the musculature and serotonin-like immunoreactive nervous system showing apical organ (ao), tentacular neurite bundle (tn) which branches (br) on the dorsal side, thin trunk neurites (trn), and nerve ring of the telotroch (nt). Ventral view; apical is to the top; preoral lobe bends backward. (E) Dorso-lateral view of the preoral lobe showing apical organ (ao), median neurite bundle (men), and branches (br) of the tentacular neurite bundle (tn). Anterior is to the right. (F) Left portion of the apical organ showing monopolar perikarya (mo) and the left group of bipolar or multipolar perikarya (lgn), which gives rise to the left branch of the tentacular neurite bundle (ltn) and median neurite bundle (mn) of the preoral lobe. Lateral view; apical is to the top; anterior of the preoral lobe is to the right. (G) Details of a monopolar perikaryon; lateral view showing perikaryon (mo) and basal projection (bp) that passes from the median part of the cell to the neuropil (np). (H) Lateral view of the preoral lobe showing anterior part of the apical organ (ao), median neurite bundle (mn), and frontal organ (fo), which is composed of several weakly stained perikarya. Anterior of the preoral lobe is to the right. (I) Dorsal commissure (dc) between two dorso-lateral branches of left (ltn) and right (rtn) branches of the tentacular neurite bundle. Dorsal view; apical is to the top. (J) Posterior view of the apical organ that is composed of two groups of bipolar or multipolar perikarya (light blue), which give rise to two dorso-lateral branches of the tentacular neurite bundle (light pink) and median neurite bundle (magenta). Monopolar perikarya form the upper large neuropil (golden). Anterior is to the right; left is to the bottom. (K) Top view of the apical organ showing large neuropil and monopolar perikarya (golden), neuropil and bipolar or multipolar perikarya (light blue), tentacular neurite bundle (light pink), median neurite bundle (magenta), and oral nerve ring (pale blue).