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Elemental enrichment of the exoskeleton of the whip spider Phrynus marginemaculatus (Arachnida: Amblypygi)

Abstract. Amblypygi is a small order of arachnids that includes the whip spiders. Like other members of the clade Pedipalpi, these arachnids are cryptic predators that use their antenniform appendages to detect prey, and spinose pedipalps for quick prey capture. To date, there is very little information on the composition of their exoskeleton despite its importance in predation and defense. Here, we performed the first analysis of a whip spider exoskeleton using energy-dispersive X-ray spectroscopy (SEM-EDS). Our studies of Phrynus marginemaculatus CL Koch, 1840 were designed to (1) determine if elemental profiles differ between instars and (2) determine if and how elemental profiles of whip spiders differ from other closely related arachnids. We found the whip spider exoskeleton to contain several trace metal elements including calcium, magnesium, manganese, potassium, sodium, and zinc. The diversity and abundance of trace elements is relatively low throughout the exoskeleton of 2nd instars but increases in adults. In particular, the chelicerae and pedipalps are well reinforced with several metal elements, most notably calcium and zinc, which are also present in the tarsal claws. A similar elemental distribution is known for adult whip scorpions (Thelyphonida). In P. marginemaculatus, these metal elements are similarly present in adult exuviae. The elemental enrichment of the whip spider exoskeleton is comparable to that present in other members of the Pedipalpi and Tetrapulmonata, reflecting a relatively conserved profile for the few species that have been examined.