Fig. 3.

Rhopalial nervous system at the ephyra to metephyra stage in Aurelia sp. 1. a–c Schematic representation. a Oral surface view with the terminal end up, the basal end down. b Aboral surface view with the terminal end up, the basal end down. c Lateral view through the center of the rhopalium with the oral side facing down. d–o Confocal sections of rhopalia labeled with antibodies against tyrosinated tubulin (tyrTub), Acetylated tubulin (acTub), taurine (Tau), GLWamide (GLW), and/or FMRFamide (FMRF). Phalloidin (Pha) is used to label filamentous actin. Nuclei are labeled with TOTO. Specimens were imaged from the oral side (d–h, j–n), from the aboral side (o) or from the lateral side (i). d A single section at a medial level. e Sections through the entire rhopalium. The tyrTub-IR neuronal processes are primarily longitudinally oriented (white arrow), but commissure-like structures form in the intermediate segment (red arrows). At the base, the processes connect to the MNN (mnn, arrowheads). f Sections through the oral ectoderm of the intermediate segment (in), with the endoderm (en) in the basal segment partially exposed. The inset shows a magnified view of a section of a cell expressing taurine at high levels. g Sections at the base of the aboral ectoderm of the intermediate segment, showing the base of the touch plate (tp) and associated neuronal processes (arrowheads). h Sections through the entire rhopalium. Note the presence of FMRFamide-IR neurites extending out of the rhopalium at its base (arrowhead). i A single section at the medial level. White arrowheads show neurites that are presumed to connect with FMRFamide-IR subepidermal sensory cells of the cup-ocellus (co), while blue arrowheads show neurites that are presumed to originate from or have neuronal connections with the FMRFamide-IR epidermal sensory cells of the spot-ocellus (so). Note the cluster of coiled cilia (ci) at the apical ends of the subepidermal sensory cells of the cup-ocellus (i′). j Sections through the oral ectoderm. Note the oral-distal cluster of FMRFamide-IR sensory cells with apical phalloidin-positive rings (pr) and knobbed cilia (bt) (inset). k A single section at the medial level, showing the FMRFamide-IR oral-proximal sensory cells (red arrows). l A single section at the medial level, showing the FMRFamide-IR oral-proximal ganglion cells whose subepidermal cell bodies are surrounded by tubulin-rich rings (yellow arrows). m Sections through the entire rhopalium. Arrowheads show GLWamide-IR neuronal processes. n A surface view of the oral ectoderm. o A surface view of the aboral ectoderm of the intermediate segment. lc lithocyst, te terminal segment, in intermediate segment, bs basal segment, en endoderm, ca rhopalar canal, o-d oral-distal group, a-l aboral-lateral group, o-c oral-central group, o-p oralproximal group, so spot-ocellus, tp touch plate, co cup-ocellus, mnn motor nerve net, dnn diffuse nerve net, bt bulbous tip of a cilium, pr phalloidin-positive ring, ci cilia, nu nucleus