Fig. 12

Exogoninae and Syllinae. Schemata of the innervation of the prostomium and achaetous segment. Structures not present in all species are shown in dotted lines, except for the dorsolateral cluster of somata, the laterofrontal sense organs and palp neurite bundle 3, which are not present in Plakosyllis brevipes but are shown in the schema in the Syllinae. The ventral root of the circumoesophageal connective forms a median dorsal and an anterior dorsal commissure most clearly visible in serotonin-lir (orange). The dorsal root of the circumoesophageal connective forms a posterior dorsal commissure, which sends fibres to the median antenna, the posterior neurite bundles and probably the lateral antennae. At least one pair of laterofrontal sense organs is located at the laterofrontal margins of the prostomium. The palps are innervated by a strong neurite bundle receiving fibres from the vrcc (possibly homologous to root 6) and possibly the drcc (possibly homologous to root 9), one neurite bundle coming from the drcc and one coming from the vrcc. The neurite bundle coming from the vrcc is missing in Plakosyllis brevipes and Prosphaerosyllis marmarae. Laterally to the main palp neurite bundle a small neurite bundle leads posteriorly towards a dorsolateral cluster of somata (turquoise) in the Syllinae. In the Exogoninae an inferior posterior cluster of somata (pink circle) receives fibres from the drcc (red arrowhead). The longitudinal neurite bundles originate from a neurite bundle marked by black arrowheads. The ventral longitudinal neurite bundle also receives fibres from a neurite bundle originating from the drcc (yellow arrowhead) which sends fibres to the posterior inferior cluster of somata (pink arrowhead) in Sph. taylori. Two segmental neurite bundles forming dorsal commissures are present on the outer margin of the achaetous segment. Abbreviations: acvr – anterior dorsal commissure of the vrcc; cc – circumoesophageal connective; dcdr – dorsal commissure of the drcc; dln – dorsa longitudinal neurite bundle; drcc – dorsal root of the circumoesophageal connective; lan – neurite bundle innervating lateral antenna; lfs – laterofrontal sense organ; lln – lateral longitudinal neurite bundle; man – neurite bundle innervating median antenna; mcvr – median dorsal commissure of the vrcc; nn – nuchal neurite bundle; pn1 – main neurite bundle innervating the palps which receives fibres from the vrcc and possibly the drcc; pn2 – neurite bundle innervating palps which originates from drcc; pn3 – neurite bundle innervating palps which originates from vrcc (presence uncertain in Prosphaerosyllis marmarae); pon – posterior neurite bundles of the brain; sn1, sn2 – segmental neurite bundles of achaetous segment; tcn – neurite bundle innervating tentacular cirrus/cirri; vln – ventral longitudinal neurite bundle; vrcc – ventral root of circumoesophageal connective; 6 – fibres possibly homologous to palp neurite bundle root 6 from vcvr; 9 – fibres possibly homologous to palp neurite bundle root 9 from drcc