The ventral nerve cord in the vestimentum of Riftia.

In the vestimentum, the paired strands of the ventral nerve cord (VNC) split and surround the ciliary field (CF, A-C). The pair of giant axons lies in each strand of the VNC (C, D). Numerous lateral neurite bundles arise from the nerve strands (E). The strands and giant axons unite at the boarder between the vestimentum and trunk (A). A–scheme of central nervous system: main elements in grey, giant axons in light grey. Anterior ends at top. Frame indicates area corresponding to histological cross sections (B-E). Stars show the levels of the corresponding sections. B–ventral nerve cord directly anteriorly to ventral ciliary field. C–ventral ciliary field (CF) surrounded by paired strands of ventral nerve cord (PNC); line shows border of ciliary field, brackets show strands of ventral nerve cord. D–close-up of left strand of ventral nerve cord, commissural neurite bundles connecting the paired strands are visible (CNC). E–lateral circular neurite bundles (LN) in epidermis. F–one of the lateral neurite bundles running in the body wall epidermis. B–brain, BV–blood vessels, CNC–commissural neurite bundles of VNC, CM–circular musculature, CF–ventral ciliary field, CIL–cilia, cpnc–central perikarya of VNC, CU–cuticle, ECM–extracellular matrix, ega–cells coating GA, EP–epidermis, GA–giant axons, LN–circular neurite bundles, lpnc–lateral perikarya of VNC, NNC–neuropile of VNC, OB–obturaculum, OP–opisthosome, PNC–paired strands of VNC surrounding CF, TR–trunk, VNC–ventral nerve cord, VT–vestimentum.