Fig. 25

Pygidial innervation in Syllidae. a1, a2: Syllis garciaib: Syllis tyrrhena. c: Plakosyllis brevipes. d: Prosphaerosyllis marmarae. e: Sphaerosyllis taylori. a1: Volume rendering of α-tubulin-lir, dorsal view. Innervation of the pygidium is segmented in green. The gut is innervated by a more differentiated nervous plexus than in anterior segments. a2: Ventral view. The ventral nerve cord drifts apart, separating into median, paramedian and main ventral nerves. The ventral nerves are connected by a pygidial commissure. From the main nerves a neurite bundle grows dorsally and innervates the pygidial cirri and possibly forms the pygidial ring commissure. B: Syllis tyrrhena. c: Plakosyllis brevipes. d: Prosphaerosyllis marmarae. e: Sphaerosyllis taylori. b-e: Maximum intensity z-projections of α-tubulin-lir, ventral sections. The innervation follows a similar pattern in all species. The ventral nerves only separate in S. garciai and Sph. taylori. Scale bars = 50 μm. Abbreviations: anu – anus; cin – cilia of intestine; mn – median ventral nerve; mvn – main ventral nerve; n – nephridium; pcm – pygidial commissure; pcn – neurite bundle innervating pygidial cirrus; pin – nervous plexus innervating intestine; pmn – paramedian ventral nerve; prn – pygidial ring neurite bundle; sp. – sensory papilla. Segmental neurite bundles in yellow: I-IV – segmental neurite bundles forming ring commissures