Fig. 2
From: Convergent evolution of the ladder-like ventral nerve cord in Annelida
The VNC of Oweniidae and Magelonidae. Cross-sections (a, b, e, g, h) and ventral view (c, d, f, i-k) of VNC in Owenia fusiformis (a-e), Myriochele heeri (f), Myriowenia sp. (b, inset), Magelona mirabilis (g, h, k) and Magelona filiformis (I, j). Anterior is up (c, d, f, k) and left (I, j). Azan staining (a, b, g), TEM (e, h), anti-5-HT (d, f, i), anti-tubulin (j) and DAPI (f, inset) staining, and 3D-reconstruction (c, k). (a, b) The VNC (vnc) in Oweniidae is situated within the epidermis. Giant fibers (gf) are reported for Myriowenia (inset). (c) Oweniids show a medullary arrangement of somata (so) and neuropil (ne) along the ventral cord, but no somata-free areas. (d) Juvenile oweniids exhibit serial clusters. (e) The ventral nerve cord (vnc) lies within the epidermis (ep). A basal lamina (bl) is present. (f) anti-5-HT and DAPI staining reveals a ventral nerve cord (vnc) with continuous appearing immunoreactive somata and lack of somata-free areas along the (vnc). (g) In magelonids the (vnc) is comprised of two anterior parallel cords and a posterior fused (vnc). (h) The (vnc) is intraepidermal and giant fibers (gf) are present. (i) The arrangement of somata can be regarded as being irregular. Commissures are present (arrowheads). (j) Anti-tubulin staining reveals parallel neurite bundles forming the (vnc) in the trunk. Commissures (co) are assembled along the medullary (vnc). (k) 3D-reconstructions verify the fusion of neurite bundles in the trunk of magelonids. bl, basal lamina; bn, branching nerve; cc, circumesophageal connective; co, commissure; cu, cuticle; ep, epidermis; gf, giant fibers; in, intestine; ln, longitudinal nerve; mu, muscle; ne, neuropil; pa, parapodia; so, somata; vnc, VNC. Scale bars = 100 μm (a, b, d, I, j, f), 50 μm (b (inset), g), 10 μm (e) and 2.5 μm (h)