Fig. 8

Syllis tyrrhena. Brain and associated clusters of somata. a, b: Schemata of the anterior end. Dotted lines indicate the position of the sections C, D and E. The neuropil of the brain is enveloped by somata (red). The nuchal lobes (green) are restricted to the achaetous segment. A pair of dorsal clusters of somata (turquoise) lie laterofrontally to the brain. c: Semi-thin cross section of the brain, slightly shifted. Drcc and vrcc enter the neuropil of the brain d: Semi-thin saggital section through the brain and nuchal organ. Somata of primary sensory cells (black arrow) and somata of the brain are hardly distinguishable. e: Oblique semi-thin cross section through the nuchal organs. Clusters of somata of support cells reach posteriorly and form a pair of nuchal lobes. Scale bars = 50 μm. Abbreviations: ae – anterior eye; bc – buccal cavity; bm – muscle penetrating the brain; br – brain; bv – blood vessel; cc – circumoesophageal connective; ccp – cells of crescent shaped ciliary patch; cun – cuticle of nuchal organ; dcs – dorsal cluster of somata; dcvr – dorsal commissure of vrcc; dlm – dorsal longitudinal muscles; drcc – dorsal root of circumoesophageal connective; es – eye spot; la -lateral antenna; lan – neurite bundle innervating lateral antenna; ma – median antenna; man – neurite bundle innervating median antenna; nn – nuchal neurite bundle; no – nuchal organ; pa – palp; pn1–3 – palp nerves 1–3; pe – posterior eyes; pon – posterior neurite bundle of the brain; tcnd – neurite bundle innervating dorsal tentacular cirrus; tcnv – neurite bundle innervating ventral tentacular cirrus; vlm – ventral longitudinal muscle; vnc – ventral nerve cord; vrcc – ventral root of circumoesophageal connective