Structure of the auditory system of the weta Hemideina crassidens (Blanchard, 1851). (Orthoptera, Ensifera, Gryllacridoidea, Stenopelmatidae). 2. Ultrastructure of the auditory sensilla.

This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae. Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap. Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrouinding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix.