Abstract
Comparative studies of the organization of nervous systems and sensory organs can reveal their evolution and specific adaptations. In the forelegs of some Ensifera (including crickets and tettigoniids), tympanal hearing organs are located in close proximity to the mechanosensitive subgenual organ (SGO). In the present study, the SGO complex in the non-hearing cave cricket Troglophilus neglectus (Rhaphidophoridae) is investigated for the neuronal innervation pattern and for organs homologous to the hearing organs in related taxa. We analyse the innervation pattern of the sensory organs (SGO and intermediate organ (IO)) and its variability between individuals. In T. neglectus, the IO consists of two major groups of closely associated sensilla with different positions. While the distal-most sensilla superficially resemble tettigoniid auditory sensilla in location and orientation, the sensory innervation does not show these two groups to be distinct organs. Though variability in the number of sensory nerve branches occurs, usually either organ is supplied by a single nerve branch. Hence, no sensory elements clearly homologous to the auditory organ are evident. In contrast to other non-hearing Ensifera, the cave cricket sensory structures are relatively simple, consistent with a plesiomorphic organization resembling sensory innervation in grasshoppers and stick insects.
Highlights
In the forelegs of some Ensifera, tympanal hearing organs are located in close proximity to the mechanosensitive subgenual organ (SGO)
In T. neglectus, the intermediate organ (IO) consists of two major groups of closely associated sensilla with different positions
The SGO complex and its innervation in T. neglectus were revealed by cobalt tracing of the leg nerves
Summary
Animals were caught in northwestern Slovenia, in a cave in the vicinity of Most na Soci They were maintained in the laboratory in terraria filled with moss, at room temperature and in constant darkness and fed with dried fish food ad libitum. The legs were cut off at the proximal femur and mounted in Sylgaard-covered glass dishes (Sylgaard 184, Suter Kunstoffe AG, Fraubrunnen, Switzerland) with insect pins under locust saline [71] (pH = 7.2). They were opened ventrally with a piece of a razor blade. As previously found [41], there were no differences in the sensory neuroanatomy between organs in different leg pairs
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