Fig. 20

Parapodial innervation on the example of Syllis garciai and Syllis tyrrhena. a1-c2: Maximum intensity projections of S. garciai. A1, B1, C1 are projections of ventral, A2, B2, C2 are projections of dorsal planes. Blue dotted lines indicate the position of the acicle, white dotted lines the position of the chaetae. a1, a2: F-actin staining showing the parapodial muscles, acicular muscles and chaetal muscles. b1, b2: α-tubulin-lir showing the individual neurite bundles forming the parapodial innervation. c1, c2: Serotonin-lir. Mainly the innervation of the acicular muscle and of the bristles is stained. d: Schema of the innervation of the parapodium in S. tyrrhena, applicable for all investigated species. View from anterior. The parapodial innervation consists of several fibre bundles. The most anterior one and the most posterior one are connected to the ventral longitudinal neurite bundle. These neurite bundles then merge to two separate bundles, the anterior parapodial neurite bundle and the thicker main parapodial neurite bundle. The main bundle splits into two roots (rp1, rp2). Fibres of rp1 reach dorsally along the parapodial plane, form a distal dorsal connective with the anterior neurite bundle on the dorsal side of the parapodium and innervate the ventral cirrus and the parapodial lobe. A neurite bundle turns back from the parapodial lobe towards the distal parapodial connective, joining the neurite bundle innervating the acicular muscles. Serotonin-lir fibres connect to the acn and form a loop around the chaeta. Fibres of root 2 reach dorsally, form a median parapodial connective to the anterior parapodial neurite bundle, innervate the dorsal cirrus, form a proximal parapodial connective to the anterior parapodial neurite bundle and form the dorsal ring commissure IIr. From this root the nervous plexus above the parapodium is formed, too. Scale bars = 50 μm. Abbreviations: acm – acicular muscles; acn – neurite bundle accompanying acicle; ap – anterior neurite bundle entering the parapodium; chm – chaetal muscles; cn – neurite bundle accompanying chaetae; dci – inclusions of dorsal cirrus in S. garciai; dcn – neurite bundle innervating dorsal cirrus; dep – dorsal epidermal plexus; dlm – dorsal longitudinal muscle; dln – dorsal longitudinal neurite bundle; dlp – distal innervation of the parapodial lobe; dpc – distal dorsal parapodial connective; inm – muscles of the intestine; int – intestine; lln – lateral longitudinal neurite bundle; mn – median ventral nerve; mp – main paraodial neurite bundle entering parapodium; mpc – median dorsal parapodial connective; mvn – main ventral nerve; n – nephridium; pln – neurite bundles innervating parapodial lobe; pm – parapodial muscle; prc – proximal dorsal parapodial connective; rp1 – root 1 of main parapodial neurite bundle; rp2 – root 2 of main parapodial neurite bundle; vcn – neurite bundle innervating ventral cirrus; vgl – ganglion of ventral neurite bundle cord; vlm – ventral longitudinal muscle; vln – ventral longitudinal neurite bundle; vnc – ventral nerve cord. Segmental neurite bundles in yellow: I-IV – segmental neurite bundles forming ring commissures; II.I-II.V – neurite bundles comprising parapodial innervation; IIr - dorsal commissure of root 2 of II