The nervous system of the nematode Sphaerolaimus gracilis (Sphaerolaimidae; Chromadorea): The regions of the renette pore, the midbody and the tail

The nervous system of the aquatic nematode Sphaerolaimus gracilis was studied by the transmission electron microscopy. The ventral nervous cord had 115 nerves in the renette pore (ventral pore) region, 109 nerves posterior to the renette pore, 47 nerves in the midbody and 8 nerves in the tail region. The dorsal cord consisted of 16 neurons, the subventral and subdorsal cords 5 nerves in the midbody. The ampulla cell of the renette pore region was under direct neuronal control and structurally like myoepithelial cells of the exocrine glands. The somatic setae were arranged in the sublateral and submedian rows. The core of the somatic setae was built up by cilia. The base of the cilia was enclosed by the sheath cell. There was a contact between the sheath cell and the central nervous system (CNS). A new hypothesis the setae-touch receptor hypothesis is presented.