URX is a set of two neurons with cell bodies that are situated sub-dorsally in the pseudocoelomic cavity just posterior to the ring neuropile. Processes project anteriorly from the cell bodies into the sub-dorsal labial process bundles and have specialized, flattened but non-ciliated endings associated with the dorsal inner labial sensilla (figure 1). A posteriorly directed process from the cell bodies loops round the ring, enters it sub-dorsally and then runs ventrally round the ring near the outside surface, ending sub-ventrally. Short branches project laterally into the regions of neuropile near the inner surface (b). The main synaptic output is to RIA and AUA (a) via exclusively dyadic synapses, to AVE on the lateral branches (b, c), to RIG (d), AVB and RIC. The main synaptic input is from URB (c) and RIR (*a). There are gap junctions to AUA, RMG and IL2. Magnifications: (a, c) x 25500, (b, d) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002