A three-dimensional immunofluorescence atlas of the brain of the hackled-orb weaver spider, .

Spider orb-web building is a captivating, rare example of animal construction, whose neural underpinnings remain undiscovered. An essential step in understanding the basis of this behavior is a foundational mapping of the spider's neuroanatomy, which has thus far been primarily studied using non-web building species. We created a three-dimensional atlas for the hackled orb-weaver, , based on immunostaining for the presynaptic component, synapsin, in whole-mounted spider synganglia. Aligned to this volume, we examined the expression patterns of neuronal populations representing many of the classical neurotransmitter and neuromodulators, as well as a subset of neuropeptides - detailing immunoreactivity in an unbiased fashion throughout the synganglion, revealing co-expression in known structures, as well as novel neuropils not evident in prior spider works. This optically-sliced, whole-mount atlas is the first of its kind for spiders, representing a substantive addition to knowledge of brain anatomy and neurotransmitter expression patterns for an orb-weaving species.