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Authors: Rubin, M., Lamsdell, J.C., Prendini, L., and Hopkins, M.J
The cuticle of scorpions (Chelicerata: Arachnida) fluoresces under long‐wave ultraviolet (UV) light due to the presence of beta‐carboline and 7‐hydroxy‐4‐methylcoumarin in the hyaline layer of the exocuticle. The adaptive significance of cuticularUVfluorescence in scorpions is debated. Although several other chelicerate orders (e.g. Opiliones and Solifugae) have been reported to fluoresce on exposure toUVlight, the prevalence of cuticularUVfluorescence has not been confirmed beyond scorpions. A systematic study of living chelicerates revealed thatUVfluorescence of the unsclerotized integument is ubiquitous across Chelicerata, whereas only scorpions and horseshoe crabs (Xiphosura) exhibit cuticularUVfluorescence. Scanning electron microscopy and histological sectioning confirmed the presence of a hyaline layer in taxa exhibiting cuticular fluorescence. The hyaline layer is absent in all other chelicerates except sea scorpions (Eurypterida) in which a taphonomically altered hyaline layer, that may have fluoresced underUVlight, was observed in exceptionally preserved cuticle. CuticularUVfluorescence appears to be associated with the presence of a hyaline layer, as has long been recognized in scorpions, and may be plesiomorphic among chelicerates. The presence of a hyaline layer in horseshoe crabs and sea scorpions suggests that several putative functions for cuticularUVfluorescence in scorpions can be discounted.