Fine structure of the CNS ganglia in the geometric spider Nephila clavata (Araneae: Nephilidae)

As web spiders usually hang with their head downward, geometrical differences in body position could affect the organization of their central nervous system (CNS). Nevertheless, most of our knowledge of spider's CNS is dependent on what has been revealed from wandering spiders. To fill the gap, we describe here the fine structural organization of the ganglionic neurons and nerves in the geometric orb web spider Nephila clavata. Nerve cells in the supraesophageal ganglion in N. clavata are packed in the frontal, dorsal and lateral regions, but the nerve cells of the subesophageal mass are only restricted to the ventral and ventrolateral regions. High resolution transmission electron microscopy (TEM) reveals the fine structural details of the neuroglial cells and the neuronal cells which have a conspicuous Golgi apparatus, rough ER, free ribosomes and well‐developed mitochondria. Comparing fine structural characteristics of the CNS ganglia with those of wandering spiders in most respects, it has been revealed that the geometrical difference may affects to the arrangement of receptors in the central body known as an important association center for web building behavior. In particular, remarkable differences can be detected in the protocerebral area by the extraordinary development of the central body including absence of the globuli and associated mushroom bodies.