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Fig. 18 | Frontiers in Zoology

Fig. 18

From: Within-family plasticity of nervous system architecture in Syllidae (Annelida, Errantia)

Fig. 18

Exogoninae. Segmental neurite bundles. aProsphaerosyllis marmarae,bSphaerosyllis taylori. A1-A4, B1-B4: Maximum intensity z-projections. a1, b1: Dorsal planes of α-tubulin-lir (grey). Diffuse nervous plexus of epidermis, strongest above parapodia. Four segmental ring neurite bundles form dorsal commissures. The dorsal longitudinal neurite bundle connects IIr to III, IV, I and IIr, proceeding from dorsolateral to mediolateral. a2, b2: Ventral, α-tubulin-lir. Four segmental neurite bundles reach laterally, then turn upwards to form a dorsal commissure each. Segmental neurite bundle II (parapodial innervation), consists of several separate neurite bundles. Yellow arrowhead: Segmental neurite bundle II and III are connected by a fine neurite bundle. a3, b3: α-tubulin-lir and cell nuclei (magenta). The ventral ganglia in Pr. marmarae are thick and well-defined. The ganglia of Sph. taylori are hardly differentiated. In the posterior part of the ganglion two commissures cross (white arrowhead in insets). a4, b4: Serotonin-lir of ventral planes. White arrows: the fourth segmental neurite bundle does not exhibit a serotonin-lir signal. Except for segmental neurite bundle IV all segmental neurite bundles and interconnections can be observed in the serotonin-lir of Pr. marmarae. The signal of segmental neurite bundles is very weak in Sph. taylori. a5, b5: Schematic drawing of the innervation of two segments. Green – neurite bundles, magenta – somata of the ventral nerve cord. a5: Several ventral papilla are innervated by segmental ring neurite bundles I and III or by additional segmental neurite bundles [1, 2]. The parapodial innervation consists of three separate bundles II.I-II.III leaving the ventral nerve cord. These are connected to each other (*). Segmental neurite bundles are linked by a ventral and lateral longitudinal neurite bundle. b5: Short neurite bundles innervate ventral papillae. The parapodial innervation II consists of four separate neurite bundles II. I – II.IV. Scale bars: Overview = 100 μm, insets = 25 μm. Abbreviations: dc – dorsal cirrus; dep – dorsal epidermal plexus; dln – dorsal longitudinal neurite bundle; int – intestine; mn – median ventral nerve; mvn – main ventral nerve; n - nephridium; pc – parapodial cluster of somata; pg – parapodial gland of Sph. taylori; pk – serotonin-lir perikarya; ppl – parapodial lobe; sp. – sensory papilla; vc – ventral cirrus; vgl – ganglion of ventral nerve cord; vln – ventral longitudinal neurite bundle; 1 – first fine segmental neurite bundle; 2 – second fine segmental neurite bundle. Segmental neurite bundles in yellow: Isrl – small root of segmental ring neurite bundle I; IIIsrl – small root of segmental ring neurite bundle III; I-IV – segmental neurite bundles forming ring commissures, all neurite bundles leaving the vnc to form the parapodial innervation are denoted by II; IIr - dorsal commissure of root 2 of II

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