Fig. 4

The VNC of Chaetopteridae and Amphinomidae. Cross-sections (a-c, g-i), ventral (d-f, j, k) and dorsal view (d, inset) of the ventral cord in Spiochaetopterus costarum (a-c), Chaetopterus variopedatus (d), Phyllochaetopterus sp. (e, f), Eurythoe complanata (g, h, j, k) and Paramphimone sp. (i). Anterior is up (e, f, j), right (d) and left (k). Azan staining (a, b, g, h), TEM (c, i), anti-5-HT (e, f) and anti-tubulin (j) staining, and 3D-reconstruction (d, k). (a, b) The (vnc) in Chaetopteridae is intraepidermal. Giant fibers are absent. (c) Ultrastructural data verify the intraepidermal position of the (vnc). (d) 3-D reconstruction of the posterior (vnc) reveals medullary arranged somata and segmental arrangement of the main commissures (co). (e) 5-HT labeling shows two parallel neurite bundles in the anterior (vnc). The esophageal nerves (en) are visible. (f) 5-HT labeling shows two parallel neurite bundles in the posterior (vnc) and segmentally and non-segmentally arranged commissures (co, also marked by yellow arrowheads). Somata aggregations are marked by yellow brackets. (g) The anterior (vnc) in Amphinomidae is intraepidermal. (h) The posterior (vnc) is located subepidermally, outside the epidermis (ep). A basal lamina (bl) interconnecting the (vnc) and the (ep) is present. (i) Ultrastructural data of the posterior (vnc) verify the presence of a basal lamina (bl) interconnecting epidermis (ep) and (vnc). (j) Anti-tubulin staining of the anterior (vnc) reveals the presence of branching nerves (bn), longitudinal nerves (ln) next to the (vnc) and commissures (co). (k) 3-D reconstruction supports the presence of hemiganglia containing the somata (so) and somata-free connectives. bl, basal lamina; bn, branching nerve; co, commissure; ep, epidermis; in, intestine; ln, longitudinal nerve; mu, muscle; ne, neuropil; so, somata; vnc, ventral nerve cord. Scale bars = 100 μm (a, b, e-h, j), 5 μm (c), and 2.5 μm (j)