Fig. 17

Histology of the ventral nerve cord. Semi-thin cross sections, toluidine blue staining. On the left are sections through the ganglion, on the right sections through the connectives, in the middle details of the ventral nerve cord. a1, a2:Prosphaerosyllis marmarae. The ventral nerve cord is separated into three ventral nerves in the region of the ganglion, a median nerve and two main nerves. The connectives are separated into several bundles (8 or 9), but a consistent number could not be identified. The bundles lie adjacent to each other. b1, b2: Sphaerosyllis taylori. Inside the ganglion the ventral nerve cord is separated into three bundles, too. The connectives are separated into several bundles, similar to Pr. Marmarae, but impossible to count. c1, c2: Plakosyllis brevipes. Three nerves can be recognised inside the ganglion and five connectives are present between ganglia, which are hardly touching each other. Segmental neurite bundle II branches off the ganglion. d1, d2: Syllis tyrrhena. Three nerves can be recognised inside the ganglion, but may fuse in some regions. Separate neurite bundles are difficult to distinguish in the connective, which seem to be fused. e1, e2: Syllis garciai. No cross sections of regions behind the proventricle were produced of S. garciai. In anterior sections separate nerves are neither in the ganglion nor in the connectives clearly distinguishable. Scale bars: Overview = 50 μm, insets = 25 μm. Abbreviations: ac – acicle; acm – acicular muscle; bl – extracellular matrix; bv – blood vessel; ch – chaetae; cp – cuticularised layer of pharynx; dc – dorsal cirrus; dlm – dorsal longitudinal muscle; dvm – dorsoventral muscles; ep – epidermal layer of pharynx; glp – paryngeal glands; int – intestine; mn – median nerve; mlp – muscular layer of pharynx; mvn – main ventral nerve; oc – oocyte; pg – parapodial gland; pmn – paramedian ventral nerve; so – somata; sp. – sensory papilla; spc – spermatocyte; vc – ventral cirrus; vlm – ventral longitudinal muscle; vm – median longitudinal muscle above ventral nerve cord. Segmental neurite bundles in yellow: II – segmental neurite bundle II