• Applied Microscopy
• /
• v.48 no.1
• /
• pp.17-26
• /
• 2018

The characteristic features of the arachnid central nervous system (CNS) are related to its body segmentation, and the body in the Opiliones appears to be a single oval structure because of its broad connection between two tagmata (prosoma and opisthosoma). Nevertheless, structural organization of the ganglionic neurons and nerves in the harvestman Leiobunum japonicum is quite similar to the CNS in most other arachnids. This paper describes the fine structural details of the main groups of neuropiles in the CNS ganglia revealed by the transmission electron microscopy. In particular, electron-microscopic features of neural clusters in the main neuroganglia of the CNS (supraesophageal ganglion, protocerebral ganglion, optic lobes, central body, and subesophageal ganglion) could provide indications for the nervous pathways associated with nerve terminations and plexuses. The CNS of this harvestman consists of a supraesophageal ganglion (brain) and a subesophageal mass, and there are no ganglia in the abdomen. Cell bodies of neuroganglia are found in the periphery, but central parts of the ganglia are mostly fibrous in all ganglia. Neuroglial cells occupy the spaces left by nerve cells. Since the nerve cells in the ganglia are typical composed of monopolar neurons, axons and dendrites of neurons are distributed along the same direction.