Abstract
BackgroundOnly a few studies have examined the visual systems of Amblypygi (whip spiders) until now. To get new insights suitable for phylogenetic analysis we studied the axonal trajectories and neuropil architecture of the visual systems of several whip spider species (Heterophrynus elaphus, Damon medius, Phrynus pseudoparvulus, and P. marginemaculatus) with different neuroanatomical techniques. The R-cell axon terminals were identified with Cobalt fills. To describe the morphology of the visual neuropils and of the protocerebrum generally we used Wigglesworth stains and μCT.ResultsThe visual system of whip spiders comprises one pair of median and three pairs of lateral eyes. The R-cells of both eye types terminate each in a first and a second visual neuropil. Furthermore, a few R-cell fibres from the median eyes leave the second median eye visual neuropil and terminate in the second lateral eye neuropil. This means R-cell terminals from the lateral eyes and the median eyes overlap. Additionally, the arcuate body and the mushroom bodies are described.ConclusionsA detailed comparison of our findings with previously studied chelicerate visual systems (i.e., Xiphosura, Scorpiones, Pseudoscorpiones, Opiliones, and Araneae) seem to support the idea of close evolutionary relationships between Xiphosura, Scorpiones, and Amblypygi.
Highlights
A few studies have examined the visual systems of Amblypygi until now
General layout of the visual system and of the protocerebrum The visual system in the studied amblypygid species is composed of one pair of median eyes located medially on the front corner of the cephalothorax, and one pair of three lateral eyes located laterally on each side of the cephalothorax (Fig. 1)
The three lateral eyes are connected to two distinct, successive visual neuropils as targets of the R-cell axons (Fig. 2)
Summary
A few studies have examined the visual systems of Amblypygi (whip spiders) until now. To get new insights suitable for phylogenetic analysis we studied the axonal trajectories and neuropil architecture of the visual systems of several whip spider species (Heterophrynus elaphus, Damon medius, Phrynus pseudoparvulus, and P. marginemaculatus) with different neuroanatomical techniques. Their main sense organs are the antenniform legs (first pair of legs) and in particular their distal tarsi These legs are no longer used for walking but are modified extremities carrying various sensilla The median eyes of whip spiders are formed from an invagination and are everted, the rhabdomeres point towards the light, and the nucleus lies basally [2, 15]. A tapetum, which reflects the incoming light towards the rhabdomeres, is Lehmann and Melzer Frontiers in Zoology (2018) 15:52
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