Identification of amphidial neurons in the different nematode species. (A) Neuronal map of the L1 larval stage the nematode Caenorhabditis elegans (reprinted from Sulston  with permission from Elsevier). The ASH neuron along with other neurons found in the same focal plane (red). The dorsal triplet amphidial neurons (green) are found in a different focal plane. The nerve ring, which surrounds the pharynx of the larva, is a process bundle with few or no cell bodies. (B-G) DIC light micrographs of the first larval stage (L1) in the different nematode species showing the amphidial cell bodies and nerve ring. B) C. elegans (N2), C) Caenorhabditis briggsae (AF16), D) Caenorhabditis sp. 3 (PS1010), E) Cruznema tripartitum (SB202), F) Pristionchus pacificus (PS312) and G) Panagrellus redivivus (PS2298). The ASH neuron (black arrowhead) is located laterally above the AUA neuron. All the neurons (ASE, ASH, AWC, AUA, ASJ) are present in the same focal plane. The SIBD and the RMD neurons posterior to the AWC neuron complete the 'Y' shaped arrangement. The nerve ring (nr) is shown (black arrow). In C. tripartitum and P. redivivus, the neurons are larger, correlating with the larger size of the nematodes. Scale bar = 50 μm.