Fig. 5

Serotonin-LIR in the nervous system of Echinoderes. Confocal z-stack projections co-labeled for 5HT-LIR (a-h), acTub-LIR (b-c, e-e’, h) and/or DNA (a, c, d, e, g). Anterior is up in all panels. Specimen silhouettes with dashed squares indicate the axial region of each corresponding z-stack. Color legend applies to all panels. a-g Echinoderes spinifurca. h Echinoderes horni. a-c Segments 1–3 in ventral views with introvert and mouth cone extended, arrowheads in (a) mark the lateral 5HT⁺ strings of the ventral nerve cord. d Segments 1–3 in lateral view with introvert and mouth cone extended. e Segments 1–4 in dorsal view with introvert and mouth cone retracted. e’ Magnified view of 5HT-LIR and acTub-LIR within the neuropil region in (e). f Dorsal view of 5HT-LIR in the neuropil and associated somata. Note the presence of four neural rings and several distinct somata (mls, vms, sds, pds) connected with the first and second rings. g Segments 8–11 in ventral view. h Segments 7–11 in ventral view. Scissor symbols mark the positions of cuticle dissection to facilitate antibody penetration. An asterisk (g-h) marks the location where the ventral nerve cord divides into left and right branches. Scale bars: 20 μm. Abbreviations: aso, anterior somata; b, brain; cne, convergent neurites; cnr, complete neural ring; inr1–2, incomplete neural rings1–2; mc, mouth cone; mcnr, mouth cone nerve ring; mls, 5HT⁺ midlateral somata; i, introvert; n, neck; np, neuropil; osn, oral styles neurites; pds, 5HT⁺ paradorsal somata; phx, pharynx; psn, primary spinoscalids neurite; pso, posterior somata; s, segment; sds, 5HT⁺subdorsal somata; sg, segmental ganglion; tn, transverse neurite; vls, 5HT⁺ ventrolateral somata; vms, 5HT⁺ ventromedial somata; vnc, ventral nerve cord; vncn, ventral nerve cord neurite; vps, 5HT⁺ ventral paired somata. Numbers after abbreviations refer to segment number