Fig. 4

Sphaerosyllis taylori. Brain and associated clusters of somata. a, b: Schemata of the prostomium, achaetous segment and first two chaetigers. Dotted lines indicate position of sections C, D and E. Segmental neurite bundles, stomatogastric neurite bundles, laterofrontal sense organs etc. omitted for better overview. The neuropil of the brain is enveloped by somata (red). The somata form a pair of posterior lobes and one posterior inferior cluster of somata (pink dotted line) is present. A pair of lateral nuchal lobes (green line) reaches posteriorly from the nuchal organs. Neurite bundles (purple) of the nuchal organ reach both into the nuchal lobes and the dorsal lobes. c: Cross section through the brain showing the neuropil and circuloesophageal connectives. d: Dorsal lobes, nuchal lobes and posterior inferior cluster of somata. e: Second chaetiger and somata of the ganglion of the ventral nerve cord extend dorsally (red), forming dorsoposterior clusters. Scale bars = 50 μm. Abbreviations: ae – anterior eye; bc – buccal cavity; br – brain; cc – circumoesophageal connective; ch – chaeta; cno – cilia of support cells of nuchal organ; cp – cuticularised layer of pharynx; dc – dorsal cirrus; dcvr – dorsal commissure of vrcc; dl – dorsal lobe; dlm – dorsal longitudinal muscle; dps – dorsoposterior cluster of somata of the ventral nerve cord only present in Sph. taylori; drcc – dorsal root of circumoesophageal connective; ep – epidermal layer of pharynx; la – lateral antenna; llm – lateral longitudinal muscle; ma – median antenna; mlp – muscular layer of pharynx; no – nuchal organ; pa – palp; pe – posterior eye; pn 1–3 – palp nerves 1–3; pon – posterior neurite bundle of the brain; ppl1 – parapodial lobe of first chaetiger; psh – pharyngeal sheath; pxm – pharynx muscle; tc – tentacular cirrus; vc – ventral cirrus; vlm – ventral longitudinal muscle; vm – ventromedian longitudinal muscle above vnc; vnc – ventral nerve cord; vrcc – ventral root of circumoesophageal connective